Techniques for Automated Software Evolution

Techniques for Automated Software
Evolution
PhD Dissertation by Raffi Khatchadourian
Computer Science & Engineering
Ohio State University

Advisor: Neelam Soundarajan
Committee: Atanas Rountev, Paul Sivilotti, Paul Evans

1

Biography

• Born in New York, NY and raised in Edison, NJ.
• First generation American.
• Family immigrated from Sofia, Bulgaria.
• Graduated from Monmouth University in 2004 with a B.S. in Computer
Science.
• Worked as:
• A Software Engineer at State of New Jersey Office of Information
Technology in Trenton, NJ.
• A UNIX Systems Administrator for pharmaceutical website in Toms
River, NJ.
• Entered PhD program at OSU in September, 2005.
• M.S. in Computer Science from OSU in March, 2010.
• Start as an RF (wireless) Systems Integration Engineer on the iPhone
development team at Apple Inc. in Cupertino, CA on Monday (4/4/2011).
2

Publication Highlights
• Raffi Khatchadourian, Phil Greenwood, Awais Rashid, and Guoqing Xu.
Pointcut rejuvenation: Recovering pointcut expressions in evolving
aspect-oriented software. IEEE Transactions on Software Engineering,
99(PrePrints), 2011. ISSN 0098-5589.
• Raffi Khatchadourian, Phil Greenwood, Awais Rashid, and Guoqing Xu.
Pointcut rejuvenation: Recovering pointcut expressions in evolving
aspect-oriented software. In Proceedings of the 24th International Conference
on Automated Software Engineering (ASE ’09), pages 575–579, Auckland, New
Zealand, November 2009. IEEE/ACM.
• Raffi Khatchadourian, Johan Dovland, and Neelam Soundarajan. Enforcing
behavioral constraints in evolving aspect-oriented programs. In
Proceedings of the 7th International Workshop on Foundations of Aspect-
Oriented Languages (FOAL ’08) at the 7th International Conference on Aspect-
Oriented Software Development (AOSD ’08), pages 19–28, Brussels, Belgium, April
2008. ACM.
• Raffi Khatchadourian, Jason Sawin, and Atanas Rountev. Automated
refactoring of legacy Java software to enumerated types. In Proceedings
of the 23rd International Conference on Software Maintenance (ICSM ’07),
pages 224–233, Paris, France, October 2007. IEEE.
• Peer-reviewed totals (2005-): 1 paper to appear in a journal, 5 papers appearing in
conference proceedings, and 5 papers appearing in workshop proceedings. 3

Activity Highlights

• Helped develop new Applied Software Engineering course ECE/CSE 668
based on Challenge-X hybrid SUV automobile simulation at OSU CAR
in 2006.
• Summer intern at Bell Labs under Rick Hull and Kedar Namjoshi
(program language design for shared-experience, multimedia, multi-
protocol, event-driven applications) in 2007.
• Visiting Graduate Research Associate with the Aspect-Oriented Software
Engineering (AOSE) Group at the Computing Department of Lancaster
University, UK under Awais Rashid in 2008.
• Visiting Researcher with the Programming Principles and Practices
(PPP) Group at the Department of Graphics and Computer Science of the
University of Tokyo under Hidehiko Masuhara in 2010.
• Proposed project mentor for Google Summer of Code (GSoC) in 2009
and 2010. Project based on refactoring to enumerated types in Java.
• Organizing committee member (Web Chair) for the European
Conference on Object-Oriented Programming (ECOOP).
4

Award Highlights

• Japan Society for the Promotion of Science
(JSPS) Summer Program Fellowship Recipient in
2010.
• National Science Foundation (NSF) East Asia
and Pacific Summer Institutes (EAPSI) Award
Recipient in 2010.
• Ohio State University Department of Computer
Science & Engineering Graduate Teaching Award
Recipient in 2010.

5

Motivation

• Software changes over
time:

6

Motivation

time:

• Requirements evolve

6

Motivation

time:

• New platforms emerge
(e.g., mobile devices)

6

Motivation

time:

• New platforms emerge
(e.g., mobile devices)

• Frameworks change
(e.g., XML vs.
annotation-based)

6

Motivation

Changing and/or maintaining large, complex software
systems can be non-trivial:
Tedious: May require changing many lines of
code.
Error-prone: Changes may be implemented
incorrectly.
Omission- May opportunities to produce better
prone: code.

7

Motivation

Adding a
parameter to a
systems can be non-trivial: method
code.
incorrectly.
prone: code.

7

Motivation

Removing a
systemsparameter may
method can be non-trivial:
alter overloading to
overriding
code.
incorrectly.
prone: code.

7

Motivation

systems can be non-trivial:
code.
HashTable vs.
incorrectly. HashMap

prone: code.

7

Approach

• Approaches made to
provide mechanical
assistance in evolution
tasks.

8

Approach

provide mechanical
tasks.

• Typically in the form of
plug-ins to IDEs.

8

Approach

provide mechanical
tasks.

plug-ins to IDEs.

• Ease the burden of
software maintenance
and evolution.

8

Approach

Restrict
workspace to only
• Approaches made to displays elements
provide mechanical relevant to the
assistance in evolution task
tasks.

plug-ins to IDEs.

• Ease the burden of
and evolution.

8

Approach

Restrict
workspace to only
• Approaches made to displays elements
provide mechanical relevant to the
assistance in evolution task
tasks.

plug-ins to IDEs.
Restructure
•code the burden of
Ease while preserving
semantics (i.e.,
and evolution.
refactoring)

8

Thesis Outline

• For my thesis, I have pursed three directions:

9

Thesis Outline

1. Mechanically alleviate burden of fragile pointcuts in
Aspect-Oriented software.

9

Thesis Outline

2.Automatically refactor legacy Java software to
language enumerated (enum) types.

9

Thesis Outline

3.Robustly specify evolving Aspect-Oriented software
components.

9

Crosscutting Concerns

/* public void invalidate() { ; * Remove the object bound with the specified name from this session. If
* ==================================================================== serverSession.removeApplicationSession(context); * the session does not have an object bound with this name, this method
* * does nothing.
* The Apache Software License, Version 1.1 // remove everything in the session /** * 
* * Standard implementation of the Session interface. This object is * After this method executes, and if the object implements
* Copyright (c) 1999 The Apache Software Foundation. All rights Enumeration enum = values.keys(); * serializable, so that it can be stored in persistent storage or transferred * <code>HttpSessionBindingListener</code>, the container calls
* reserved. while (enum.hasMoreElements()) { * to a different JVM for distributable session support. * <code>valueUnbound()</code> on the object.
* String name = (String)enum.nextElement(); * *
* Redistribution and use in source and binary forms, with or without removeValue(name); * IMPLEMENTATION NOTE: An instance of this class represents both the * @param name Name of the object to remove from this session.
* modification, are permitted provided that the following conditions } * internal (Session) and application level (HttpSession) view of the session. *
* are met: * However, because the class itself is not declared public, Java logic outside * @exception IllegalStateException if this method is called on an
* valid = false; * of the <code>org.apache.tomcat.session</code> package cannot cast an * invalidated session
* 1. Redistributions of source code must retain the above copyright } * HttpSession view of this instance back to a Session view. */
* notice, this list of conditions and the following disclaimer. * public void removeAttribute(String name) {
* public boolean isNew() { * @author Craig R. McClanahan
* 2. Redistributions in binary form must reproduce the above copyright if (! valid) { * @version $Revision: 1.2 $ $Date: 2000/05/15 17:54:10 $ synchronized (attributes) {
* notice, this list of conditions and the following disclaimer in String msg = sm.getString("applicationSession.session.ise"); */ Object object = attributes.get(name);
* the documentation and/or other materials provided with the if (object == null)
* distribution. throw new IllegalStateException(msg); final class StandardSession return;
* } implements HttpSession, Session { attributes.remove(name);
* 3. The end-user documentation included with the redistribution, if // System.out.println( "Removing attribute " + name );
* any, must include the following acknowledgment: if (thisAccessTime == creationTime) { /** if (object instanceof HttpSessionBindingListener) {
* "This product includes software developed by the return true; // ----------------------------------------------------------- Constructors * Update the accessed time information for this session. This method ((HttpSessionBindingListener) object).valueUnbound
* Apache Software Foundation (http://www.apache.org/)." } else { * should be called by the context when a request comes in for a particular (new HttpSessionBindingEvent((HttpSession) this, name));
* Alternately, this acknowledgment may appear in the software return false; * session, even if the application does not reference it. }
itself, } /** */ }
* if and wherever such third-party acknowledgments normally appear. } * Construct a new Session associated with the specified Manager. public void access() {
* * }
* 4. The names "The Jakarta Project", "Tomcat", and "Apache Software * @param manager The manager with which this Session is associated this.lastAccessedTime = this.thisAccessedTime;
* Foundation" must not be used to endorse or promote products /** */ this.thisAccessedTime = System.currentTimeMillis(); * Bind an object to this session, using the specified name. If an object
derived * @deprecated public StandardSession(Manager manager) { this.isNew=false; * of the same name is already bound to this session, the object is
* from this software without prior written permission. For written */ } * replaced.
* permission, please contact apache@apache.org. super(); * 
* public void putValue(String name, Object value) { this.manager = manager; * After this method executes, and if the object implements
* 5. Products derived from this software may not be called "Apache" setAttribute(name, value); /** * <code>HttpSessionBindingListener</code>, the container calls
* nor may "Apache" appear in their names without prior written } } * Perform the internal processing required to invalidate this session, * <code>valueBound()</code> on the object.
* permission of the Apache Group. * without triggering an exception if the session has already expired. *
* public void setAttribute(String name, Object value) { */ * @param name Name to which the object is bound, cannot be null
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED if (! valid) { /** public void expire() { * @param value Object to be bound, cannot be null
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES String msg = sm.getString("applicationSession.session.ise"); * The last accessed time for this Session. *
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE */ // Remove this session from our manager's active sessions * @exception IllegalArgumentException if an attempt is made to add a
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR throw new IllegalStateException(msg); private long lastAccessedTime = creationTime; if ((manager != null) && (manager instanceof ManagerBase)) * non-serializable object in an environment marked distributable.
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, } ((ManagerBase) manager).remove(this); * @exception IllegalStateException if this method is called on an
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * invalidated session
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF if (name == null) { /** // Unbind any objects associated with this session */
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND String msg = sm.getString("applicationSession.value.iae"); * The Manager with which this Session is associated. Vector results = new Vector(); public void setAttribute(String name, Object value) {
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, */ Enumeration attrs = getAttributeNames();
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT throw new IllegalArgumentException(msg); private Manager manager = null; while (attrs.hasMoreElements()) { if ((manager != null) && manager.getDistributable() &&
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF } String attr = (String) attrs.nextElement(); !(value instanceof Serializable))
* SUCH DAMAGE. results.addElement(attr); throw new IllegalArgumentException
* ==================================================================== removeValue(name); // remove any existing binding /** } (sm.getString("standardSession.setAttribute.iae"));
* * The maximum time interval, in seconds, between client requests before Enumeration names = results.elements();
* This software consists of voluntary contributions made by many if (value != null && value instanceof HttpSessionBindingListener) { * the servlet container may invalidate this session. A negative time while (names.hasMoreElements()) { synchronized (attributes) {
* individuals on behalf of the Apache Software Foundation. For more HttpSessionBindingEvent e = * indicates that the session should never time out. String name = (String) names.nextElement(); removeAttribute(name);
* information on the Apache Software Foundation, please see new HttpSessionBindingEvent(this, name); */ removeAttribute(name); attributes.put(name, value);
* <http://www.apache.org/>. private int maxInactiveInterval = -1; } if (value instanceof HttpSessionBindingListener)
* ((HttpSessionBindingListener)value).valueBound(e); ((HttpSessionBindingListener) value).valueBound
* [Additional notices, if required by prior licensing conditions] } // Mark this session as invalid (new HttpSessionBindingEvent((HttpSession) this, name));
* /** setValid(false); }
*/ values.put(name, value); * Flag indicating whether this session is new or not.
} */ } }
private boolean isNew = true;
/**
package org.apache.tomcat.session; * @deprecated /** // -------------------------------------------- HttpSession Private Methods
*/ /**
import org.apache.tomcat.core.*; public Object getValue(String name) { * Flag indicating whether this session is valid or not. }
import org.apache.tomcat.util.StringManager; return getAttribute(name); */ /**
import java.io.*; } private boolean isValid = false; * Read a serialized version of this session object from the specified
import java.net.*; /** * object input stream.
import java.util.*; public Object getAttribute(String name) { * Set the <code>isNew</code> flag for this session. * 
import javax.servlet.*; if (! valid) { /** * * IMPLEMENTATION NOTE: The reference to the owning Manager
import javax.servlet.http.*; String msg = sm.getString("applicationSession.session.ise"); * The string manager for this package. * @param isNew The new value for the <code>isNew</code> flag * is not restored by this method, and must be set explicitly.
*/ */ *
/** throw new IllegalStateException(msg); private StringManager sm = void setNew(boolean isNew) { * @param stream The input stream to read from
* Core implementation of an application level session } StringManager.getManager("org.apache.tomcat.session"); *
* this.isNew = isNew; * @exception ClassNotFoundException if an unknown class is specified
* @author James Duncan Davidson [duncan@eng.sun.com] if (name == null) { * @exception IOException if an input/output error occurs
* @author Jason Hunter [jch@eng.sun.com] String msg = sm.getString("applicationSession.value.iae"); /** } */
* @author James Todd [gonzo@eng.sun.com] * The HTTP session context associated with this session. private void readObject(ObjectInputStream stream)
*/ throw new IllegalArgumentException(msg); */ throws ClassNotFoundException, IOException {
} private static HttpSessionContext sessionContext = null; /**
public class ApplicationSession implements HttpSession { * Set the <code>isValid</code> flag for this session. // Deserialize the scalar instance variables (except Manager)
return values.get(name); * creationTime = ((Long) stream.readObject()).longValue();
private StringManager sm = } /** * @param isValid The new value for the <code>isValid</code> flag id = (String) stream.readObject();
StringManager.getManager("org.apache.tomcat.session"); * The current accessed time for this session. */ lastAccessedTime = ((Long) stream.readObject()).longValue();
private Hashtable values = new Hashtable(); /** */ void setValid(boolean isValid) { maxInactiveInterval = ((Integer) stream.readObject()).intValue();
private String id; * @deprecated private long thisAccessedTime = creationTime; isNew = ((Boolean) stream.readObject()).booleanValue();
private ServerSession serverSession; */ this.isValid = isValid; isValid = ((Boolean) stream.readObject()).booleanValue();
private Context context; public String[] getValueNames() { }
private long creationTime = System.currentTimeMillis();; Enumeration e = getAttributeNames(); // Deserialize the attribute count and attribute values
private long thisAccessTime = creationTime; Vector names = new Vector(); int n = ((Integer) stream.readObject()).intValue();
private long lastAccessed = creationTime; // ----------------------------------------------------- Session Properties // ------------------------------------------------- HttpSession Properties for (int i = 0; i < n; i++) {
private int inactiveInterval = -1; while (e.hasMoreElements()) { String name = (String) stream.readObject();
private boolean valid = true; names.addElement(e.nextElement()); Object value = (Object) stream.readObject();
} /** /** attributes.put(name, value);
ApplicationSession(String id, ServerSession serverSession, * Set the creation time for this session. This method is called by the * Return the time when this session was created, in milliseconds since }
Context context) { String[] valueNames = new String[names.size()]; * Manager when an existing Session instance is reused. * midnight, January 1, 1970 GMT.
this.serverSession = serverSession; * * }
this.context = context; names.copyInto(valueNames); * @param time The new creation time * @exception IllegalStateException if this method is called on an
this.id = id; */ * invalidated session
return valueNames; public void setCreationTime(long time) { */ /**
this.inactiveInterval = context.getSessionTimeOut(); public long getCreationTime() { * Write a serialized version of this session object to the specified
} this.creationTime = time; * object output stream.
if (this.inactiveInterval != -1) { this.lastAccessedTime = time; return (this.creationTime); * 
this.inactiveInterval *= 60; public Enumeration getAttributeNames() { this.thisAccessedTime = time; * IMPLEMENTATION NOTE: The owning Manager will not be stored
} if (! valid) { } * in the serialized representation of this Session. After calling
} String msg = sm.getString("applicationSession.session.ise"); * <code>readObject()</code>, you must set the associated Manager
* explicitly.
ServerSession getServerSession() { throw new IllegalStateException(msg); /** * 
return serverSession; } * Return the session context with which this session is associated. * IMPLEMENTATION NOTE: Any attribute that is not Serializable
} * * will be silently ignored. If you do not want any such attributes,
Hashtable valuesClone = (Hashtable)values.clone(); * @deprecated As of Version 2.1, this method is deprecated and has no * be sure the <code>distributable</code> property of our associated
/** * replacement. It will be removed in a future version of the * Manager is set to <code>true</code>.
* Called by context when request comes in so that accesses and return (Enumeration)valuesClone.keys(); * Java Servlet API. *
* inactivities can be dealt with accordingly. } */ * @param stream The output stream to write to
*/ public HttpSessionContext getSessionContext() { *
* @exception IOException if an input/output error occurs
void accessed() { /** if (sessionContext == null) */
// set last accessed to thisAccessTime as it will be left over * @deprecated sessionContext = new StandardSessionContext(); private void writeObject(ObjectOutputStream stream) throws IOException {
// from the previous access */ return (sessionContext);
lastAccessed = thisAccessTime; // Write the scalar instance variables (except Manager)
thisAccessTime = System.currentTimeMillis(); public void removeValue(String name) { } stream.writeObject(new Long(creationTime));
removeAttribute(name); stream.writeObject(id);
validate(); } stream.writeObject(new Long(lastAccessedTime));
} // ----------------------------------------------HttpSession Public Methods stream.writeObject(new Integer(maxInactiveInterval));
public void removeAttribute(String name) { stream.writeObject(new Boolean(isNew));
void validate() { if (! valid) { } stream.writeObject(new Boolean(isValid));
// if we have an inactive interval, check to see if we've exceeded it String msg = sm.getString("applicationSession.session.ise"); /**
if (inactiveInterval != -1) { * Return the object bound with the specified name in this session, or // Accumulate the names of serializable attributes
int thisInterval = throw new IllegalStateException(msg); * <code>null</code> if no object is bound with that name. Vector results = new Vector();
(int)(System.currentTimeMillis() - lastAccessed) / 1000; } * Enumeration attrs = getAttributeNames();
* @param name Name of the attribute to be returned while (attrs.hasMoreElements()) {
if (thisInterval > inactiveInterval) { if (name == null) { * String attr = (String) attrs.nextElement();
invalidate(); String msg = sm.getString("applicationSession.value.iae"); * @exception IllegalStateException if this method is called on an Object value = attributes.get(attr);
} * invalidated session if (value instanceof Serializable)
} throw new IllegalArgumentException(msg); */ results.addElement(attr);
} } public Object getAttribute(String name) { }

// HTTP SESSION IMPLEMENTATION METHODS Object o = values.get(name); return (attributes.get(name)); // Serialize the attribute count and the attribute values
stream.writeObject(new Integer(results.size()));
public String getId() { if (o instanceof HttpSessionBindingListener) { } Enumeration names = results.elements();
if (valid) { HttpSessionBindingEvent e = while (names.hasMoreElements()) {
return id; new HttpSessionBindingEvent(this,name); String name = (String) names.nextElement();
} else { /** stream.writeObject(name);
String msg = sm.getString("applicationSession.session.ise"); ((HttpSessionBindingListener)o).valueUnbound(e); * Return an <code>Enumeration</code> of <code>String</code> objects stream.writeObject(attributes.get(name));
} * containing the names of the objects bound to this session. }
throw new IllegalStateException(msg); *
} values.remove(name); * @exception IllegalStateException if this method is called on an
} } * invalidated session }
*/
public long getCreationTime() { public void setMaxInactiveInterval(int interval) { public Enumeration getAttributeNames() { crosscut invalidate(StandardSession s): s & (int getMaxInactiveInterval() |
if (valid) { if (! valid) { long getCreationTime() |
return creationTime; String msg = sm.getString("applicationSession.session.ise"); return (attributes.keys()); Object getAttribute(String) |
} else { Enumeration getAttributeNames() |
String msg = sm.getString("applicationSession.session.ise"); throw new IllegalStateException(msg); } String[] getValueNames() |
} void invalidate() |
throw new IllegalStateException(msg); boolean isNew() |
} /** void removeAttribute(String) |
} * Return the object bound with the specified name in this session, or void setAttribute(String, Object));
* <code>null</code> if no object is bound with that name.
/** * static advice(StandardSession s): invalidate(s) {
* * @param name Name of the value to be returned before {
* @deprecated * if (!s.isValid())
* @exception IllegalStateException if this method is called on an throw new IllegalStateException
* invalidated session (s.sm.getString("standardSession."
* + thisJoinPoint.methodName
* @deprecated As of Version 2.2, this method is replaced by + ".ise"));
* <code>getAttribute()</code> }
*/ }
/** public Object getValue(String name) {
* Return the session identifier for this session.
*/ return (getAttribute(name));
public String getId() {
} }

/** // -------------------------------------------------------------- Private Class
* Return the set of names of objects bound to this session. If there
* are no such objects, a zero-length array is returned.
* /**
* @exception IllegalStateException if this method is called on an * This class is a dummy implementation of the <code>HttpSessionContext</code>
* invalidated session * interface, to conform to the requirement that such an object be returned
* * when <code>HttpSession.getSessionContext()</code> is called.
* @deprecated As of Version 2.2, this method is replaced by *
* <code>getAttributeNames()</code> * @author Craig R. McClanahan
*/ *
public String[] getValueNames() { * @deprecated As of Java Servlet API 2.1 with no replacement. The
* interface will be removed in a future version of this API.
Vector results = new Vector(); */
Enumeration attrs = getAttributeNames();
while (attrs.hasMoreElements()) { final class StandardSessionContext implements HttpSessionContext {
String attr = (String) attrs.nextElement();
results.addElement(attr);
} private Vector dummy = new Vector();
return (this.id); String names[] = new String[results.size()];
for (int i = 0; i < names.length; i++) /**
names[i] = (String) results.elementAt(i); * Return the session identifiers of all sessions defined
return (names); * within this context.
*
} * @deprecated As of Java Servlet API 2.1 with no replacement.
* This method must return an empty <code>Enumeration</code>
* and will be removed in a future version of the API.
/** */
* Invalidates this session and unbinds any objects bound to it. public Enumeration getIds() {
*
* @exception IllegalStateException if this method is called on return (dummy.elements());
* an invalidated session
*/
public void invalidate() {

// Cause this session to expire
expire();

}

} /**
* Return <code>true</code> if the client does not yet know about the
* session, or if the client chooses not to join the session. For
* example, if the server used only cookie-based sessions, and the client
* has disabled the use of cookies, then a session would be new on each
* request.
*
* @exception IllegalStateException if this method is called on an
* invalidated session
*/
public boolean isNew() {

return (this.isNew);

}

package org.apache.tomcat.session; void validate() {
// if we have an inactive interval, check to see if
import org.apache.tomcat.core.*; // we've exceeded it
import org.apache.tomcat.util.StringManager;
import java.io.*; if (inactiveInterval != -1) {
import java.net.*; int thisInterval =
import java.util.*; (int)(System.currentTimeMillis() - lastAccessed) / 1000;
import javax.servlet.*;
import javax.servlet.http.*; if (thisInterval > inactiveInterval) {
invalidate();
/**
* Core implementation of a server session ServerSessionManager ssm =
* ServerSessionManager.getManager();
* @author James Duncan Davidson [duncan@eng.sun.com]
* @author James Todd [gonzo@eng.sun.com] ssm.removeSession(this);
*/ }
}
public class ServerSession { }

private StringManager sm = synchronized void invalidate() {
StringManager.getManager("org.apache.tomcat.session"); Enumeration enum = appSessions.keys(); /**
private Hashtable values = new Hashtable(); * Set the session identifier for this session.
private Hashtable appSessions = new Hashtable(); while (enum.hasMoreElements()) { *
private String id; Object key = enum.nextElement(); * @param id The new session identifier
private long creationTime = System.currentTimeMillis();; ApplicationSession appSession = */
private long thisAccessTime = creationTime; (ApplicationSession)appSessions.get(key); public void setId(String id) {
private long lastAccessed = creationTime;
private int inactiveInterval = -1; appSession.invalidate();
}
ServerSession(String id) { }
this.id = id;
} public void putValue(String name, Object value) {
if (name == null) {
public String getId() { String msg = sm.getString("serverSession.value.iae");
return id;
} throw new IllegalArgumentException(msg);
}
public long getCreationTime() {
return creationTime; removeValue(name); // remove any existing binding
} values.put(name, value);
}
public long getLastAccessedTime() {
return lastAccessed; public Object getValue(String name) {
} if (name == null) {
String msg = sm.getString("serverSession.value.iae");
public ApplicationSession getApplicationSession(Context context,
boolean create) { throw new IllegalArgumentException(msg);
ApplicationSession appSession = } if ((this.id != null) && (manager != null) &&
(ApplicationSession)appSessions.get(context); (manager instanceof ManagerBase))
return values.get(name); ((ManagerBase) manager).remove(this);
if (appSession == null && create) { }

// XXX public Enumeration getValueNames() {
// sync to ensure valid? return values.keys();
}
appSession = new ApplicationSession(id, this, context);
appSessions.put(context, appSession); public void removeValue(String name) {
} values.remove(name);
}
// XXX
// make sure that we haven't gone over the end of our public void setMaxInactiveInterval(int interval) {
// inactive interval -- if so, invalidate and create inactiveInterval = interval;
// a new appSession }

return appSession; public int getMaxInactiveInterval() {
} return inactiveInterval;
}
void removeApplicationSession(Context context) {
appSessions.remove(context); // XXX
} // sync'd for safty -- no other thread should be getting something
// from this while we are reaping. This isn't the most optimal
/** // solution for this, but we'll determine something else later. this.id = id;
* Called by context when request comes in so that accesses and
* inactivities can be dealt with accordingly. synchronized void reap() {
*/ Enumeration enum = appSessions.keys();

void accessed() { while (enum.hasMoreElements()) {
// set last accessed to thisAccessTime as it will be left over

if ((manager != null) && (manager instanceof ManagerBase))
((ManagerBase) manager).add(this);

}

/**
* Return descriptive information about this Session implementation and
* the corresponding version number, in the format
* <code><description>/<version></code>.
*/
public String getInfo() {

return (this.info);

}

/**
* Return the last time the client sent a request associated with this
* session, as the number of milliseconds since midnight, January 1, 1970
* GMT. Actions that your application takes, such as getting or setting
* a value associated with the session, do not affect the access time.
*/

return (this.lastAccessedTime);

}

/**
* Return the Manager within which this Session is valid.
*/
public Manager getManager() {

return (this.manager);

}

/**
* Set the Manager within which this Session is valid.
*
* @param manager The new Manager
*/
public void setManager(Manager manager) {

10


* * does nothing.
itself, } /** */ }
* * }

• Crosscutting concerns
} */ } }
/**
*/ /**
*/ */ *

(CCCs) affect many
* explicitly.

heterogeneous software


modules.
*/
*/ }
} }

/** // -------------------------------------------------------------- Private Class
* /**
*/ *
*
/** */
*
*/

expire();

}

} /**
* request.
*
*/


}

invalidate();
/**
*/ }
}

}
this.id = id;
if (name == null) {
return id;
}
}

}
}
// XXX

}



}

/**
*/

return (this.info);

}

/**
*/


}

/**
*/


}

/**
*
*/

10


* * does nothing.
itself, } /** */ }
* * }

} */ } }
/**
*/ /**
*/ */ *

(CCCs) affect many
* explicitly.



modules.
*/
*/ }
} }

/** // -------------------------------------------------------------- Private Class
* /**
*/ *
*
/** */
*

• Code is:
*/

expire();

}

} /**
* request.
*
*/


}

invalidate();
/**
*/ }
}

}
this.id = id;
if (name == null) {
return id;
}
}

}
}
// XXX

}



}

/**
*/

return (this.info);

}

/**
*/


}

/**
*/


}

/**
*
*/

10


* * does nothing.
itself, } /** */ }
* * }

} */ } }
/**
*/ /**
*/ */ *

(CCCs) affect many
* explicitly.



modules.
*/
*/ }
} }

/** // -------------------------------------------------------------- Private Class
* /**
*/ *
*
/** */
*

• Code is:
*/

expire();

}

} /**
* request.
*
*/


}

invalidate();
/**
*/ }
}

}
this.id = id;
if (name == null) {
return id;
}
}

• Scattered throughout

}
}
// XXX

}


many modules.

}

/**
*/

return (this.info);

}

/**
*/


}

/**
*/


}

/**
*
*/

10


* * does nothing.
itself, } /** */ }
* * }

} */ } }
/**
*/ /**
*/ */ *

(CCCs) affect many
* explicitly.



modules.
*/
*/ }
} }

/** // -------------------------------------------------------------- Private Class
* /**
*/ *
*
/** */
*

• Code is:
*/

expire();

}

} /**
* request.
*
*/


}

invalidate();
/**
*/ }
}

}
this.id = id;
if (name == null) {
return id;
}
}


}
}
// XXX

}


many modules.

}

• Tangled with unrelated
/**
*/

return (this.info);

modules. }

/**
*/


}

/**
*/


}

/**
*
*/

10


* * does nothing.
itself, } /** */ }
* * }

} */ } }
/**
*/ /**
*/ */ *

(CCCs) affect many
* explicitly.


Message


modules.
*/

encryption is an
*/ }
} }

/** // -------------------------------------------------------------- Private Class
* /**
*/ *
*
/** */

example since many
*

• Code is:
*/

expire();

}

} /**
* request.
*
*/


}


parts of a program
invalidate();
/**
*/ }
}

}
this.id = id;
if (name == null) {
return id;
}
}


involve security
}
}
// XXX

}


many modules.

}

• Tangled with unrelated
/**
*/

return (this.info);

modules. }

/**
*/


}

/**
*/


}

/**
*
*/

10

Aspect-Oriented Programming

* ==================================================================== serverSession.removeApplicationSession(context); /** * the session does not have an object bound with this name, this method
* * Perform the internal processing required to invalidate this session, * does nothing.
* The Apache Software License, Version 1.1 // remove everything in the session /** * without triggering an exception if the session has already expired. * 
* * Standard implementation of the Session interface. This object is */ * After this method executes, and if the object implements
* Copyright (c) 1999 The Apache Software Foundation. All rights Enumeration enum = values.keys(); * serializable, so that it can be stored in persistent storage or transferred public void expire() { * <code>HttpSessionBindingListener</code>, the container calls
* String name = (String)enum.nextElement(); * // Remove this session from our manager's active sessions *
* Redistribution and use in source and binary forms, with or without removeValue(name); * IMPLEMENTATION NOTE: An instance of this class represents both the if ((manager != null) && (manager instanceof ManagerBase)) * @param name Name of the object to remove from this session.
* modification, are permitted provided that the following conditions } * internal (Session) and application level (HttpSession) view of the session. ((ManagerBase) manager).remove(this); *
* valid = false; * of the <code>org.apache.tomcat.session</code> package cannot cast an // Unbind any objects associated with this session * invalidated session
* 1. Redistributions of source code must retain the above copyright } * HttpSession view of this instance back to a Session view. Vector results = new Vector(); */
* notice, this list of conditions and the following disclaimer. * Enumeration attrs = getAttributeNames(); public void removeAttribute(String name) {
* public boolean isNew() { * @author Craig R. McClanahan while (attrs.hasMoreElements()) {
* 2. Redistributions in binary form must reproduce the above copyright if (! valid) { * @version $Revision: 1.2 $ $Date: 2000/05/15 17:54:10 $ String attr = (String) attrs.nextElement(); synchronized (attributes) {
* notice, this list of conditions and the following disclaimer in String msg = sm.getString("applicationSession.session.ise"); */ results.addElement(attr); Object object = attributes.get(name);
* the documentation and/or other materials provided with the } if (object == null)
* distribution. throw new IllegalStateException(msg); final class StandardSession Enumeration names = results.elements(); return;
* } implements HttpSession, Session { while (names.hasMoreElements()) { attributes.remove(name);
* 3. The end-user documentation included with the redistribution, if String name = (String) names.nextElement(); // System.out.println( "Removing attribute " + name );
* any, must include the following acknowledgment: if (thisAccessTime == creationTime) { removeAttribute(name); if (object instanceof HttpSessionBindingListener) {
* "This product includes software developed by the return true; // ----------------------------------------------------------- Constructors } ((HttpSessionBindingListener) object).valueUnbound
* Apache Software Foundation (http://www.apache.org/)." } else { (new HttpSessionBindingEvent((HttpSession) this, name));
* Alternately, this acknowledgment may appear in the software return false; // Mark this session as invalid }
itself, } /** setValid(false); }
* if and wherever such third-party acknowledgments normally appear. } * Construct a new Session associated with the specified Manager.
* * } }
* 4. The names "The Jakarta Project", "Tomcat", and "Apache Software * @param manager The manager with which this Session is associated
* Foundation" must not be used to endorse or promote products /** */ * Bind an object to this session, using the specified name. If an object
derived * @deprecated public StandardSession(Manager manager) { /** * of the same name is already bound to this session, the object is
* from this software without prior written permission. For written */ * replaced.
* permission, please contact apache@apache.org. super(); } * 
* 5. Products derived from this software may not be called "Apache" setAttribute(name, value); * <code>HttpSessionBindingListener</code>, the container calls
* nor may "Apache" appear in their names without prior written } } /** * <code>valueBound()</code> on the object.
* permission of the Apache Group. * Set the <code>isNew</code> flag for this session. *
* public void setAttribute(String name, Object value) { * * @param name Name to which the object is bound, cannot be null
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED if (! valid) { /** * @param isNew The new value for the <code>isNew</code> flag * @param value Object to be bound, cannot be null
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES String msg = sm.getString("applicationSession.session.ise"); * The last accessed time for this Session. */ *
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE */ void setNew(boolean isNew) { * @exception IllegalArgumentException if an attempt is made to add a
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR throw new IllegalStateException(msg); private long lastAccessedTime = creationTime; * non-serializable object in an environment marked distributable.
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, } this.isNew = isNew; * @exception IllegalStateException if this method is called on an
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF if (name == null) { /** } */
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND String msg = sm.getString("applicationSession.value.iae"); * The Manager with which this Session is associated. public void setAttribute(String name, Object value) {
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, */
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT throw new IllegalArgumentException(msg); private Manager manager = null; /** if ((manager != null) && manager.getDistributable() &&
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF } * Set the <code>isValid</code> flag for this session. !(value instanceof Serializable))
* SUCH DAMAGE. * throw new IllegalArgumentException
* ==================================================================== removeValue(name); // remove any existing binding /** * @param isValid The new value for the <code>isValid</code> flag (sm.getString("standardSession.setAttribute.iae"));
* * The maximum time interval, in seconds, between client requests before */
* This software consists of voluntary contributions made by many if (value != null && value instanceof HttpSessionBindingListener) { * the servlet container may invalidate this session. A negative time void setValid(boolean isValid) { synchronized (attributes) {
* individuals on behalf of the Apache Software Foundation. For more HttpSessionBindingEvent e = * indicates that the session should never time out. removeAttribute(name);
* information on the Apache Software Foundation, please see new HttpSessionBindingEvent(this, name); */ this.isValid = isValid; attributes.put(name, value);
* [Additional notices, if required by prior licensing conditions] } (new HttpSessionBindingEvent((HttpSession) this, name));
* /** // ------------------------------------------------- HttpSession Properties }
} */ }
private boolean isNew = true; /**
/** * Return the time when this session was created, in milliseconds since
package org.apache.tomcat.session; * @deprecated * midnight, January 1, 1970 GMT. // -------------------------------------------- HttpSession Private Methods
*/ /** *
import org.apache.tomcat.core.*; public Object getValue(String name) { * Flag indicating whether this session is valid or not. * @exception IllegalStateException if this method is called on an
import org.apache.tomcat.util.StringManager; return getAttribute(name); */ * invalidated session /**
import java.io.*; } private boolean isValid = false; */ * Read a serialized version of this session object from the specified
import java.net.*; public long getCreationTime() { * object input stream.
import java.util.*; public Object getAttribute(String name) { * 
import javax.servlet.*; if (! valid) { /** return (this.creationTime); * IMPLEMENTATION NOTE: The reference to the owning Manager
import javax.servlet.http.*; String msg = sm.getString("applicationSession.session.ise"); * The string manager for this package. * is not restored by this method, and must be set explicitly.
*/ } *
/** throw new IllegalStateException(msg); private StringManager sm = * @param stream The input stream to read from
* /** * @exception ClassNotFoundException if an unknown class is specified
* @author James Duncan Davidson [duncan@eng.sun.com] if (name == null) { * Return the session context with which this session is associated. * @exception IOException if an input/output error occurs
* @author Jason Hunter [jch@eng.sun.com] String msg = sm.getString("applicationSession.value.iae"); /** * */
* @author James Todd [gonzo@eng.sun.com] * The HTTP session context associated with this session. * @deprecated As of Version 2.1, this method is deprecated and has no private void readObject(ObjectInputStream stream)
*/ throw new IllegalArgumentException(msg); */ * replacement. It will be removed in a future version of the throws ClassNotFoundException, IOException {
} private static HttpSessionContext sessionContext = null; * Java Servlet API.
public class ApplicationSession implements HttpSession { */ // Deserialize the scalar instance variables (except Manager)
return values.get(name); public HttpSessionContext getSessionContext() { creationTime = ((Long) stream.readObject()).
private StringManager sm = } /** isValid = ((Boolean) stream.readObject()).booleanValue();
StringManager.getManager("org.apache.tomcat.session"); * The current accessed time for this session. if (sessionContext == null)
private Hashtable values = new Hashtable(); /** */ sessionContext = new StandardSessionContext(); // Deserialize the attribute count and attribute values
private String id; * @deprecated private long thisAccessedTime = creationTime; return (sessionContext); int n = ((Integer) stream.readObject()).intValue();
private ServerSession serverSession; */ for (int i = 0; i < n; i++) {
private Context context; public String[] getValueNames() { } String name = (String) stream.readObject();
private long creationTime = System.currentTimeMillis();; Enumeration e = getAttributeNames(); Object value = (Object) stream.readObject();
private long thisAccessTime = creationTime; Vector names = new Vector(); attributes.put(name, value);
private boolean valid = true; // ----------------------------------------------------- Session Properties // ----------------------------------------------HttpSession Public Methods }
while (e.hasMoreElements()) {
ApplicationSession(String id, ServerSession serverSession, names.addElement(e.nextElement()); }
Context context) { } /** /**
this.serverSession = serverSession; * Set the creation time for this session. This method is called by the * Return the object bound with the specified name in this session, or
this.context = context; String[] valueNames = new String[names.size()]; * Manager when an existing Session instance is reused. * <code>null</code> if no object is bound with that name. /**
this.id = id; * * * Write a serialized version of this session object to the specified
names.copyInto(valueNames); * @param time The new creation time * @param name Name of the attribute to be returned * object output stream.
this.inactiveInterval = context.getSessionTimeOut(); */ * * 
return valueNames; public void setCreationTime(long time) { * @exception IllegalStateException if this method is called on an * IMPLEMENTATION NOTE: The owning Manager will not be stored
if (this.inactiveInterval != -1) { * invalidated session * in the serialized representation of this Session. After calling
this.inactiveInterval *= 60; } this.creationTime = time; */ * <code>readObject()</code>, you must set the associated Manager
} this.lastAccessedTime = time; public Object getAttribute(String name) { * explicitly.
} public Enumeration getAttributeNames() { this.thisAccessedTime = time; * 
if (! valid) { return (attributes.get(name)); * IMPLEMENTATION NOTE: Any attribute that is not Serializable
ServerSession getServerSession() { String msg = sm.getString("applicationSession.session.ise"); } * will be silently ignored. If you do not want any such attributes,
return serverSession; } * be sure the <code>distributable</code> property of our associated
} throw new IllegalStateException(msg); * Manager is set to <code>true</code>.
} /** *
/** * Return the session identifier for this session. /** * @param stream The output stream to write to
* Called by context when request comes in so that accesses and Hashtable valuesClone = (Hashtable)values.clone(); */ * Return an <code>Enumeration</code> of <code>String</code> objects *
* inactivities can be dealt with accordingly. public String getId() { * containing the names of the objects bound to this session. * @exception IOException if an input/output error occurs
*/ return (Enumeration)valuesClone.keys(); * */
} return (this.id); * @exception IllegalStateException if this method is called on an private void writeObject(ObjectOutputStream stream) throws IOException {
// HTTP SESSION IMPLEMENTATION METHODS } */ // Write the scalar instance variables (except Manager)
/** public Enumeration getAttributeNames() { stream.writeObject(new Long(creationTime));
public String getId() { * @deprecated stream.writeObject(id);
if (valid) { */ /** return (attributes.keys()); stream.writeObject(new Long(lastAccessedTime));
return id; * Set the session identifier for this session. stream.writeObject(new Integer(maxInactiveInterval));
} else { public void removeValue(String name) { * } stream.writeObject(new Boolean(isNew));
String msg = sm.getString("applicationSession.session.ise"); removeAttribute(name); * @param id The new session identifier stream.writeObject(new Boolean(isValid));
} */
throw new IllegalStateException(msg); public void setId(String id) { /** // Accumulate the names of serializable attributes
} public void removeAttribute(String name) { * Return the object bound with the specified name in this session, or Vector results = new Vector();
} if (! valid) { if ((this.id != null) && (manager != null) && * <code>null</code> if no object is bound with that name. Enumeration attrs = getAttributeNames();
String msg = sm.getString("applicationSession.session.ise"); (manager instanceof ManagerBase)) * while (attrs.hasMoreElements()) {
public long getCreationTime() { ((ManagerBase) manager).remove(this); * @param name Name of the value to be returned String attr = (String) attrs.nextElement();
if (valid) { throw new IllegalStateException(msg); * Object value = attributes.get(attr);
return creationTime; } this.id = id; * @exception IllegalStateException if this method is called on an if (value instanceof Serializable)
} else { * invalidated session results.addElement(attr);
String msg = sm.getString("applicationSession.session.ise"); if (name == null) { if ((manager != null) && (manager instanceof ManagerBase)) * }
String msg = sm.getString("applicationSession.value.iae"); ((ManagerBase) manager).add(this); * @deprecated As of Version 2.2, this method is replaced by
throw new IllegalStateException(msg); * <code>getAttribute()</code> // Serialize the attribute count and the attribute values
} throw new IllegalArgumentException(msg); } */ stream.writeObject(new Integer(results.size()));
} } public Object getValue(String name) { Enumeration names = results.elements();
while (names.hasMoreElements()) {
/** Object o = values.get(name); /** return (getAttribute(name)); String name = (String) names.nextElement();
* * Return descriptive information about this Session implementation and stream.writeObject(name);
* @deprecated if (o instanceof HttpSessionBindingListener) { * the corresponding version number, in the format } stream.writeObject(attributes.get(name));
*/ HttpSessionBindingEvent e = * <code><description>/<version></code>. }
new HttpSessionBindingEvent(this,name); */
public HttpSessionContext getSessionContext() { public String getInfo() { /**
return new SessionContextImpl(); ((HttpSessionBindingListener)o).valueUnbound(e); * Return the set of names of objects bound to this session. If there }
} } return (this.info); * are no such objects, a zero-length array is returned.
* crosscut invalidate(StandardSession s): s & (int getMaxInactiveInterval() |
values.remove(name); } * @exception IllegalStateException if this method is called on an long getCreationTime() |
} * invalidated session Object getAttribute(String) |
/** * Enumeration getAttributeNames() |
public void setMaxInactiveInterval(int interval) { * Return the Manager within which this Session is valid. * @deprecated As of Version 2.2, this method is replaced by String[] getValueNames() |
if (! valid) { */ * <code>getAttributeNames()</code> void invalidate() |
String msg = sm.getString("applicationSession.session.ise"); public Manager getManager() { */ boolean isNew() |
public String[] getValueNames() { void removeAttribute(String) |
throw new IllegalStateException(msg); return (this.manager); void setAttribute(String, Object));
} Vector results = new Vector();
} Enumeration attrs = getAttributeNames(); static advice(StandardSession s): invalidate(s) {
inactiveInterval = interval; while (attrs.hasMoreElements()) { before {
} String attr = (String) attrs.nextElement(); if (!s.isValid())
/** results.addElement(attr); throw new IllegalStateException
public int getMaxInactiveInterval() { * Set the Manager within which this Session is valid. } (s.sm.getString("standardSession."
if (! valid) { * String names[] = new String[results.size()]; + thisJoinPoint.methodName
String msg = sm.getString("applicationSession.session.ise"); * @param manager The new Manager for (int i = 0; i < names.length; i++) + ".ise"));
*/ names[i] = (String) results.elementAt(i); }
throw new IllegalStateException(msg); public void setManager(Manager manager) { return (names); }
}
this.manager = manager; }
return inactiveInterval;
} }
} /** }
* Invalidates this session and unbinds any objects bound to it.
/** *
//----------------------------------------------------------------------- * Return the maximum time interval, in seconds, between client requests * @exception IllegalStateException if this method is called on // -------------------------------------------------------------- Private Class
* before the servlet container will invalidate the session. A negative * an invalidated session
* time indicates that the session should never time out. */
* public void invalidate() { /**
* @exception IllegalStateException if this method is called on * This class is a dummy implementation of the <code>HttpSessionContext</code>
* an invalidated session // Cause this session to expire * interface, to conform to the requirement that such an object be returned
*/ expire(); * when <code>HttpSession.getSessionContext()</code> is called.
public int getMaxInactiveInterval() { *
} * @author Craig R. McClanahan
return (this.maxInactiveInterval); *
* @deprecated As of Java Servlet API 2.1 with no replacement. The
/** * interface will be removed in a future version of this API.
* Return <code>true</code> if the client does not yet know about the */
* example, if the server used only cookie-based sessions, and the client final class StandardSessionContext implements HttpSessionContext {
* request.
* private Vector dummy = new Vector();
* invalidated session /**
*/ * Return the session identifiers of all sessions defined
public boolean isNew() { * within this context.
*
return (this.isNew); * @deprecated As of Java Servlet API 2.1 with no replacement.
} * and will be removed in a future version of the API.
*/
public Enumeration getIds() {

return (dummy.elements());

}

/**
* Return the <code>HttpSession</code> associated with the
* specified session identifier.
*
* @param id Session identifier for which to look up a session
*
* @deprecated As of Java Servlet API 2.1 with no replacement.
* This method must return null and will be removed in a
* future version of the API.
*/
public HttpSession getSession(String id) {

return (null);

}

}

package org.apache.tomcat.session; ynchronized void invalidate() {
Enumeration enum = appSessions.keys();
import org.apache.tomcat.core.*;
import org.apache.tomcat.util.StringManager; while (enum.hasMoreElements()) {
import java.io.*; Object key = enum.nextElement();
import java.net.*; ApplicationSession appSession =
import java.util.*; (ApplicationSession)appSessions.get(key);
import javax.servlet.http.*; appSession.invalidate();
}
/** }
* Core implementation of a server session
* public void putValue(String name, Object value) {
* @author James Duncan Davidson [duncan@eng.sun.com] if (name == null) {
* @author James Todd [gonzo@eng.sun.com] String msg = sm.getString("serverSession.value.iae");
*/
throw new IllegalArgumentException(msg);

private StringManager sm = removeValue(name); // remove any existing binding
StringManager.getManager("org.apache.tomcat.session"); values.put(name, value);
private Hashtable values = new Hashtable(); }
private Hashtable appSessions = new Hashtable();
private String id; public Object getValue(String name) {
private long creationTime = System.currentTimeMillis();; if (name == null) {
private long thisAccessTime = creationTime; String msg = sm.getString("serverSession.value.iae");
private int inactiveInterval = -1; throw new IllegalArgumentException(msg);
}
ServerSession(String id) {
this.id = id; return values.get(name);
} }

public String getId() { public Enumeration getValueNames() {
return id; return values.keys();
} }

public long getCreationTime() { public void removeValue(String name) {
return creationTime; values.remove(name);
} }

public long getLastAccessedTime() { public void setMaxInactiveInterval(int interval) {
return lastAccessed; inactiveInterval = interval;
} }

public ApplicationSession getApplicationSession(Context context, public int getMaxInactiveInterval() {
boolean create) { return inactiveInterval;
ApplicationSession appSession = }
(ApplicationSession)appSessions.get(context);
// XXX
if (appSession == null && create) { // sync'd for safty -- no other thread should be getting something
// XXX // solution for this, but we'll determine something else later.
// sync to ensure valid?
synchronized void reap() {
appSession = new ApplicationSession(id, this, context); Enumeration enum = appSessions.keys();
appSessions.put(context, appSession);
} while (enum.hasMoreElements()) {
Object key = enum.nextElement();
// XXX ApplicationSession appSession =
// make sure that we haven't gone over the end of our (ApplicationSession)appSessions.get(key);
// inactive interval -- if so, invalidate and create
// a new appSession appSession.validate();
}
return appSession; }
} }

appSessions.remove(context);
}

/**
* inactivities can be dealt with accordingly.
*/

void validate()

private long lastAccessed = creationTime; if (inactiveInterval != -1) {
private int inactiveInterval = -1; int thisInterval =
(int)(System.currentTimeMillis() - lastAccessed) / 1000;
void accessed() {
// set last accessed to thisAccessTime as it will be left over if (thisInterval > inactiveInterval) {
// from the previous access invalidate();
lastAccessed = thisAccessTime;
thisAccessTime = System.currentTimeMillis(); ServerSessionManager ssm =
ServerSessionManager.getManager();
validate();
} ssm.removeSession(this);
}
void validate() { }
// if we have an inactive interval, check to see if we've exceeded it }
if (inactiveInterval != -1) {
int thisInterval = private long lastAccessedTime = creationTime;

if (thisInterval > inactiveInterval) {
invalidate(); /**
} * Return the last time the client sent a request associated with this
} * session, as the number of milliseconds since midnight, January 1, 1970
} * GMT. Actions that your application takes, such as getting or setting
public long getLastAccessedTime() { */
if (valid) { public long getLastAccessedTime() {
return lastAccessed;
} else { return (this.lastAccessedTime);
String msg = sm.getString("applicationSession.session.ise");
}
throw new IllegalStateException(msg);
}
} this.lastAccessedTime = time;

}


void accessed() {
// from the previous access

thisAccessTime = System.currentTimeMillis();

}

11


* * } }

•
} */ }

Aspect-Oriented
*/ /** *
*/ } *

Programming enables
} /** *
} */

localized implementations
}

of CCCs.
} }
} /** }
/** *
* request.
*
*/


}

/**
*
*
*/

return (null);

}

}

}
/** }
*/

}
} }

} }

} }

} }

// XXX
}
} }

}

/**
*/

void validate()

void accessed() {
validate();
}
void validate() { }

invalidate(); /**
}
}

}


void accessed() {


}

11


* * } }

•
} */ }

Aspect-Oriented
*/ /** *
*/ } *

Programming enables
} /** *
} */

}

of CCCs.
} }
} /** }
/** *
* request.
*
*/


}

/**
*
*
*/

return (null);

}

}

• Pointcuts select (join)
points in the program
where a CCC applies.
}
/** }
*/

}
} }

} }

} }

} }

// XXX
}
} }

}

/**
*/

void validate()

void accessed() {
validate();
}
void validate() { }

invalidate(); /**
}
}

}


void accessed() {


}

11


* * } }

•
} */ }

Aspect-Oriented
*/ /** *
*/ } *

Programming enables
} /** *
} */

}

of CCCs.
} }
} /** }
/** *
* request.
*
*/


}

/**
*
*
*/

return (null);

}

}

• Pointcuts select (join)
points in the program
where a CCC applies.
}
/** }
*/

}
} }

} }

} }

} }

// XXX

•
}

Code (advice) is implicitly
} }

}

/**
*/

void validate()

executed at those points.
void accessed() {
validate();
}
void validate() { }

invalidate(); /**
}
}

}


void accessed() {


}

11


* * } }

•
} */ }

Aspect-Oriented
*/ /** *
*/ } *

Programming enables
} /** *
} */

}

of CCCs.
} }
} /** }
/** *
* request.
*
*/


}

/**
*
*
*/

return (null);

}

}

• Pointcuts select (join) Aspects
points in the program allow code to be
where a CCC applies. localized into a
}
/** }
*/

}
} }

} }


single module
} }

} }

// XXX

•
}

Code (advice) is implicitly
} }

}

/**
*/

void validate()

executed at those points.
void accessed() {
validate();
}
void validate() { }

invalidate(); /**
}
}

}


void accessed() {


}

11

Message Encryption Example

12


messageSent():
execution(* send*(..))

12


messageSent():
execution(* send*(..))

The
execution of all
methods whose name
begins with “send”
must have their
messages encrypted.
12

Fragile Pointcut Problem

13


• A pointcut is robust iff it
continues to select points
where the CCC applies in
subsequent base-code
versions without textual
modification.

13


modification.

• Otherwise, a pointcut is
fragile.

13


modification.

• Otherwise, a pointcut is
fragile.

• Fragile pointcuts can
cause software to
silently malfunction!

13

Pointcut fragility Example

14


• Suppose a subsequent version, a new method is
added that sends messages but whose name begins
with “transmit?”

14


• Our pointcut breaks as a result.

14


• Our pointcut breaks as a result.
• Thus, messageSent() is a fragile pointcut.

14

My Approach to the Fragile Pointcut Problem

15


• Developed an approach that mechanically aids
developers in suitably updating pointcuts upon
changes to the base-code.

15


• The approach analyzes arbitrarily deep structural
commonalities between program elements
associated with pointcuts in a particular software
version.

15


• The approach analyzes arbitrarily deep structural
commonalities between program elements
associated with pointcuts in a particular software
version.
• The extracted patterns are then applied to later
versions to suggest additional join points that may
require inclusion.

15

Contributions

• Commonality identification:
• Developed an open source Eclipse IDE plug-in called
REJUVENATE POINTCUT that finds new join points
exhibiting structural properties similar to those
already selected by a pointcut.

16

Contributions

• Correlation analysis:
• Empirically establish that join points selected by a
single pointcut typically portray a significant amount
of unique structural commonality on multiple fronts.

16

Contributions

• Correlation analysis:
• Empirically establish that join points selected by a
single pointcut typically portray a significant amount
of unique structural commonality on multiple fronts.
• Expression recovery:
• Evaluated usefulness by rejuvenating pointcuts in
multiple versions of three open source AO projects. 16

Abstract Example Base Code

package p;
class A {
int f;
void m1() {
int a = f + 1;
}
void m2() {
int b = f + 2;
}
void n() {
f = 3;
}
}
17


package p;
class A {
• Two methods whose int f;
name begins with the
character m. void m1
m1() {
int a = f + 1;
}
void m2
m2() {
int b = f + 2;
}
void n() {
f = 3;
}
}
17


package p;
class A {
character m. void m1() {
int a = f + 1;
• One method whose name }
does not begin with the
character m.
void m2() {
int b = f + 2;
}
void n
n() {
f = 3;
}
}
17


package p;
class A {
f
int a = f + 1;
character m.
void m2() {
int b = f + 2;
• Method bodies of m1 and }
m2 read from a field f. void n() {
f = 3;
}
}
17


package p;
class A {
f
int a = f + 1;
character m.
void m2() {
int b = f + 2;
• Method bodies of m1 and }
m2 read from a field f. void n() {
f = 3;
• Method body of n writes }
to field f.
}
17

Pointcut Example

pointcut mayBeFragile() :
execution(* m*(..));

18

Pointcut Example


• Selects m1() and m2()
but not n().

18

Pointcut Example


but not n().

• Assume that correct join
points are selected.

18

Pointcut Example


but not n().

• Assume that correct join
points are selected.

CCC
applies to m1 and m2
but not p.
18

void p() {
int d = f + 4; A new method
} is added to the base
code

19

void p() {
int d = f + 4;
}


W
ha
ta
po bo
int ut
cu th
t? e

19

void p() {
int d = f + 4;
}


• Same pointcut selects m1() and m2() but not
n() and p().

19

void p() {
int d = f + 4;
}


n() and p().

• Assume CCC applies to p().

19

void p() {
int d = f + 4;
}


n() and p().

• mayBeFragile() is fragile!

19

void p() {
int d = f + 4;
}


n() and p().

• p() silently fall out of pointcut’s scope.
19

void p() {
int d = f + 4;
}


n() and p().

• p() silently fall out of pointcut’s scope.
• May be difficult to identify in large base codes. 19

Phase I: Leverage Structural Commonality

20

• Build a Concern Graph [Robillard, Murphy ’02].

m1
gets declares

f gets m2 declares A
sets declares

n
20

• Extract commonalities between currently selected
join points.

m1
gets declares

sets declares

n
20

• Extract commonalities between currently selected
join points.
• Find common sinks and sources in the graph.
m1
gets (A,declares,?)
declares

f (?,gets, f)
gets m2 declares A
sets declares

n
20

Evaluating Patterns
[Dagenais, Breu, Warr, Robillard ’07]
(?,gets, f) (A,declares,?)

m1
gets declares

sets declares

n
21

Evaluating Patterns

{m1,m2}
m1
gets declares

sets declares

n
21

Evaluating Patterns
100%
conﬁdence!

{m1,m2}
m1
gets declares

sets declares

n
21

Evaluating Patterns
100%
conﬁdence!

{m1,m2} {m1,m2,n}
m1
gets declares

sets declares

n
21

Evaluating Patterns
100% 66%
conﬁdence! conﬁdence

{m1,m2} {m1,m2,n}
m1
gets declares

sets declares

n
21

Storing patterns for Phase II

100% 66%
conﬁdence! conﬁdence

XML

22

Storing patterns for Phase II

XML

22

It’s a little more complicated ...

23

• Pattern evaluation is done on several other different levels.

23

• Previously illustrated the α evaluation:

23

• Considers the strength of the structural relationships between
elements produced by the pattern and those selected by the
pointcut.

23

pointcut.

• Another dimension is the β evaluation:

23

pointcut.

• Considers the completeness of the structural relationship
expressed by the pattern compared to relationships expressed
by the pointcut.

23

pointcut.

by the pointcut.
• Lastly, there is an abstractness evaluation:

23

pointcut.

by the pointcut.
• Considers the ratio of wild-cards (?) to concrete elements in
the pattern as patterns can be arbitrarily deep.

23

pointcut.

by the pointcut.
• Considers the ratio of wild-cards (?) to concrete elements in
the pattern as patterns can be arbitrarily deep.
• All three dimensions are combined to produce a patterns
confidence value. 23

SACTIONS OF SOFTWARE ENGINEERING, VOL. X, NO. Y, Z 20AB


0 if |Match(ˆ , Paths(CG + ))| = 0
π
err α (ˆ , PCE)
π = |PCE ∩ Match(ˆ , Paths(CG + ))|
π
1 − + otherwise
|Match(ˆ , Paths(CG ))|
π

1 if |PCE| = 0
err β (ˆ , PCE)
π = |PCE ∩ Match(ˆ , Paths(CG + ))|
π
1 − otherwise
|PCE|

1 if |ˆ | = 0
π
abs(ˆ )
π = |ˆ | − |W(ˆ )|
π π
1 − otherwise
|ˆ |
π
conf (ˆ , PCE)
π = 1 − [err α (ˆ , PCE)(1 − abs(ˆ )) + err β (ˆ , PCE)abs(ˆ )]
π π π π

Pattern attribute equations.

allSpeed). Thus, the err α rate for this pattern projection of wild card elements contained
e PCE found on line 3 of Figure 2, which selects π . Likewise, |W(ˆ )| represents the number o
ˆ π
ution of methods DieselEngine.increase(Fuel) and elements contained within pattern π . Then, t
ˆ 24

All join points

25 25

All join points
Pointcut

25 25

All join points
Pointcut

Pattern

25 25

All join points
Pointcut

Pattern

α

25 25

All join points
Pointcut
β
Pattern

α

25 25

All join points
Pointcut
β
Pattern

α

A ? ? ? ?
25 25

All join points
Pointcut
β
Pattern

α

A ? ? ? ?
abs
25 25

Phase II: Expression Recovery

26


void p() {
code

26


void p() {
code
m1
gets declares

sets declares

gets n declares

p
26


void p() {
code
m1
(?,gets, f)
gets (A,declares,?)
declares

sets declares

gets n declares

XML
p
26

(?,gets, f)

{m1,m2,p}

27 27

(?,gets, f)
100%
conﬁdence!

{m1,m2,p}

27 27

(?,gets, f) execution(* m*(..))
100%
conﬁdence!

{m1,m2,p}

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2}

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2} = {p}

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2} = {p}

(A,declares,?)

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2} = {p}

(A,declares,?)

{m1,m2,n,p}

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2} = {p}

(A,declares,?)

66%
conﬁdence
{m1,m2,n,p}

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2} = {p}

(A,declares,?) execution(* m*(..))

66%
conﬁdence
{m1,m2,n,p}

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2} = {p}


66%
conﬁdence
{m1,m2,n,p} {m1,m2}

27 27

100%
conﬁdence!

{m1,m2,p} {m1,m2} = {p}


66%
conﬁdence
{m1,m2,n,p} {m1,m2} = {n,p}

27 27

100%
confidence!

{m1,m2,p} {m1,m2} = {p}


66%
confidence
{m1,m2,n,p} {m1,m2} = {n,p}

p is suggested with (100 + 66) / 2 ≈ 83% confidence

27 27

100%
confidence!

{m1,m2,p} {m1,m2} = {p}


66%
confidence
{m1,m2,n,p} {m1,m2} = {n,p}

n is suggested with 66% confidence

27 27

100%
confidence!

{m1,m2,p} {m1,m2} = {p}


66%
confidence
{m1,m2,n,p} {m1,m2} = {n,p}

n is suggested with 66% confidence
execution(* m*(..)) || execution (* p())
27 27

100%
confidence!

{m1,m2,p} {m1,m2} = {p}


66%
confidence
{m1,m2,n,p} {m1,m2} = {n,p}

p is suggested with (100 + 66) / 2 ≈ 83% Suggestions
confidence
n is suggested with 66% confidence sorted by confidence
in IDE
execution(* m*(..)) || execution (* p())
27 27

mplementation Implementation

28

Evaluation: Phase I
subject KL. cls. PC shd. KP. α β t (s)
AJHotDraw 21.8 298 32 90 3.36 0.32 0.06 101
Ants 1.57 33 22 297 1.25 0.15 0.23 43
Bean 0.12 2 2 4 0.02 0.24 0.23 4
Contract4J 10.7 199 15 350 1.80 0.26 0.44 115
DCM 1.68 29 8 343 2.47 0.15 0.45 4
Figure 0.10 5 1 6 0.02 0.11 0.45 8
Glassbox 26.0 430 55 208 2.62 0.1 0.29 228
HealthWatcher 5.72 76 27 122 1.00 0.21 0.16 22
Cactus 7.57 93 4 222 2.15 0.21 0.52 8
LoD 1.59 29 5 164 0.54 0.15 0.41 46
MobilePhoto 3.80 52 25 25 0.78 0.23 0.00 11
MySQLa 44.0 187 2 3016 17.6 0.12 0.58 379
NullCheck 1.47 27 1 112 0.10 0.17 0.55 293
N-Version 0.55 15 4 9 0.08 0.19 0.24 1
Quicksort 0.07 3 4 7 0.06 0.19 0.15 3
RacerAJ 0.58 13 4 9 0.02 0.23 0.09 5
RecoveryCache 0.22 3 4 14 0.07 0.11 0.21 6
Spacewar 1.42 21 9 58 0.23 0.15 0.22 37
StarJ-Pool 38.2 511 1 3 0.07 0.25 0.00 75
Telecom 0.28 10 4 5 0.03 0.21 0.02 7
Tetris 1.04 8 18 27 0.50 0.16 0.01 14
TollSystem 5.20 88 35 85 1.68 0.26 0.06 20
Tracing 0.37 5 16 132 0.68 0.17 0.4 1
Totals: 174 2137 298 5308 37.1 0.18 0.16 1431
29

Evaluation: Phase I
subject KL. cls. PC shd. KP. α β t (s)
AJHotDraw 21.8 298 32 90 3.36 0.32 0.06 101
Ants 1.57 33 22 297 1.25 0.15 0.23 43
Bean 0.12 2 2 4 0.02 0.24 0.23 4
Contract4J 10.7 199 15 350 1.80 0.26 0.44 115
DCM 1.68 29 8 343 2.47 0.15 0.45 4
Figure 0.10 5 1 6 0.02 0.11 0.45 8
Glassbox 26.0 430 55 208 2.62 0.1 0.29 228
HealthWatcher 5.72 76 27 122 1.00 0.21 0.16 22
Cactus 7.57 93 4 222 2.15 0.21 0.52 8
LoD 1.59 29 5 164 0.54 0.15 0.41 46
MobilePhoto 3.80 52 25 25 0.78 0.23 0.00 11
MySQLa 44.0 187 2 3016 17.6 0.12 0.58 379
NullCheck 1.47 27 1 112 0.10 0.17 0.55 293
N-Version 0.55 15 4 9 0.08 0.19 0.24 1
Quicksort 0.07 3 4 7 0.06 0.19 0.15 3
RacerAJ 0.58 13 4 9 0.02 0.23 0.09 5

4.8 secs per
RecoveryCache
Spacewar
0.22
1.42
3
21
4
9
14 0.07 0.11 0.21
58 0.23 0.15 0.22
6
37
pointcut StarJ-Pool
Telecom
38.2 511
0.28 10
1
4
3 0.07 0.25 0.00
5 0.03 0.21 0.02
75
7
Tetris 1.04 8 18 27 0.50 0.16 0.01 14
TollSystem 5.20 88 35 85 1.68 0.26 0.06 20
Tracing 0.37 5 16 132 0.68 0.17 0.4 1
Totals: 174 2137 298 5308 37.1 0.18 0.16 1431
29

Evaluation: Phase 2

30

Evaluation: Phase 2

• Applied to 3 multi-versioned AspectJ projects.

30

Evaluation: Phase 2

• Rejuvenated pointcuts (49 in total) over major
releases (20 in total).

30

Evaluation: Phase 2

• Maximum pattern length set to 2 edges.

30

Evaluation: Phase 2

• Able to identify 93% of new shadows introduced in
later versions that were not selected by previous
pointcut representations.

30

Evaluation: Phase 2

• On average, 3.97 suggestions appeared before true
positives.

30

Evaluation: Phase 2

• On average, 3.97 suggestions appeared before true
positives.
• On average, 10.95 secs. required to rejuvenate a
pointcut.
30

Related Work

• Wloka et al. [AOSD 08] automatically modify PCEs
upon automated base code refactoring.

31

Related Work

• Base code changes must only be administered by
automated refactoring.

31

Related Work


RP works with
arbitrary changes

31

Related Work

• Adding new base code also breaks pointcuts.

31

Related Work

• AspectJ Development Tools (AJDT) and Ye and
Volder [AOSD 08] display join points that are
currently and almost selected by a pointcut.

31

Related Work

• Do not analyze the differences exhibited by join
points between base code versions.

31

Related Work

• Do not analyze the differences exhibited by join
• Pointcut Doctor uses heuristics general to all AO
systems. 31

Related Work

Volder [AOSD 08] display join points thatuses
RP are
heuristics
customized to a
•Do not analyze the differences exhibited by join
particular system
• Pointcut Doctor uses heuristics general to all AO
systems. 31

Conclusion

• Aspect-Oriented Programming localize
implementations of CCCs that would otherwise be
scattered throughout the system and tangled with
unrelated code.

32

Conclusion

unrelated code.
• Evolving Aspect-Oriented programs requires some
special consideration, especially regarding pointcut
fragility.

32

Conclusion

unrelated code.
fragility.
• Rejuvenating pointcuts can be non-trivial in large
systems.

32

Conclusion

unrelated code.
fragility.
• Rejuvenating pointcuts can be non-trivial in large
systems.
• Mechanical assistance that leverages structural
commonality can ease the evolution process.
32

Java 5 Enums

• Java 5 introduced a rich set of new features such as
generics, metadata annotations, boxing/unboxing,
and type-safe enumerations.

Java 5 Enums

• Using enums increases:

Java 5 Enums

• Type-safety.

Java 5 Enums

• Type-safety.
• Code comprehension.

Java 5 Enums

• Type-safety.
• Code simplicity.

Java 5 Enums

• Type-safety.
• Resiliency related to separate compilation.

Java 5 Enums

• Type-safety.
• Enums replaced a variety of coding patterns used to
compensate for their absence in legacy software.

Java 5 Enums

• Type-safety.
• Enums replaced a variety of coding patterns used to
compensate for their absence in legacy software.
• Leaves a large body of code to be manually upgraded.

Motivating Example

class TrafficSignal {
public static final int RED = 0;
public static final int YELLOW = 1;
public static final int GREEN = 2;
/∗ Current color of the trafﬁc signal, initially red by default ∗/
private int color = RED;
/∗ Accessor for the light’s current color ∗/
public int getColor() {return this.color;}}

class Automobile {
private static final int IDLE = 0;
private static final int INCREASE_SPEED = 1;
private static final int DECREASE_SPEED = 2;
private static final int STOP = 3; 34

Motivating Example

Weak Enum
Pattern

class Automobile {

Motivating Example


class Automobile {
Type Safety

Motivating Example

Manual
Enumeration

class Automobile {

Motivating Example

Namespacing

class Automobile {

Motivating Example

private int color = RED; Brittle

class Automobile {

Motivating Example Revisited


class Automobile {


class TrafficSignal {{
TrafficSignal
public enum Color {RED, RED = 0;
public static final int
YELLOW,
GREEN};
/∗ Current color of the trafﬁc signal, initially red byby default ∗/
/* Current color of the trafﬁc signal, initially red default */
private Color color= =RED;
private int color Color.RED;
/∗ Accessor for the light’s current color */∗/
/* Accessor for the light’s current color
public Color getColor(){return this.color;}}

class Automobile {
class Automobile {
private enum Action {IDLE,IDLE = 0;
private static final int
INCREASE_SPEED,
DECREASE_SPEED,
STOP};
private static final int MAX_SPEED = 140;
private
static final int STOP = 3; 35


class TrafficSignal
YELLOW,
GREEN};

class Automobile {
class Automobile {
INCREASE_SPEED,
DECREASE_SPEED,
STOP};
private
static final int STOP = 3; 35


TrafficSignal
public enum Color {RED,
YELLOW,
YELLOW,
GREEN};
GREEN};
/* Current color of the trafﬁc signal, initially red by default */
private Color color = Color.RED;
/* Accessor for the light’s current color */
public Color getColor() {return this.color;}}
int getColor() {return this.color;}}

class Automobile {
class Automobile {
class Automobile {
private enum Action {IDLE,
INCREASE_SPEED,
INCREASE_SPEED,
DECREASE_SPEED,
DECREASE_SPEED,
STOP};
STOP}; static final int STOP = 3;
private 35


TrafficSignal
YELLOW,
YELLOW,
GREEN};
GREEN};

class Automobile {
class Automobile {
class Automobile {
INCREASE_SPEED,
INCREASE_SPEED,
DECREASE_SPEED,
DECREASE_SPEED,
STOP};
private 36


Language Enum
TrafficSignal
YELLOW,
YELLOW,
GREEN};
GREEN};

class Automobile {
class Automobile {
class Automobile {
INCREASE_SPEED,
INCREASE_SPEED,
DECREASE_SPEED,
DECREASE_SPEED,
STOP};
private 36


TrafficSignal
YELLOW,
YELLOW,
GREEN};
GREEN};

class Automobile {
class Automobile {
class Automobile {
Type Safety
INCREASE_SPEED,
INCREASE_SPEED,
DECREASE_SPEED,
DECREASE_SPEED,
STOP};
private 36


TrafficSignal
YELLOW,
YELLOW,
GREEN};
GREEN}; Singletons in initially red by default */
/* Current color of the trafﬁc signal,
colorOrder
private ColorNatural = =RED;

class Automobile {
class Automobile {
class Automobile {
INCREASE_SPEED,
INCREASE_SPEED,
DECREASE_SPEED,
DECREASE_SPEED,
STOP};
private 36


TrafficSignal
YELLOW,
YELLOW,
GREEN};
GREEN};
public Color getColor(){return Preﬁxed
int getColor() {return this.color;}} this.color;}}

class Automobile {
class Automobile {
class Automobile {
INCREASE_SPEED,
INCREASE_SPEED,
DECREASE_SPEED,
DECREASE_SPEED,
STOP};
private 36

Supports
Separate
Compilation
TrafficSignal
YELLOW,
YELLOW,
GREEN};
GREEN};

class Automobile {
class Automobile {
class Automobile {
INCREASE_SPEED,
INCREASE_SPEED,
DECREASE_SPEED,
DECREASE_SPEED,
STOP};
private 36

this.currentAction &&
private int color = RED; 38 (reacti
INCREASE_SPEED ||automobile is currently performing, idle by default ∗/
/∗ The action this
private for currentAction =
tSpeed <= MAX_SPEED))
Traffic Signal Client
/∗ Accessorintthe light’s current color ∗/IDLE; 39 this.c
public intspeed of the automobile, initially 540
getColor() {return this.color;}} this.
/∗ The current
rmAction(reaction);} mph. ∗/
41
private int currentSpeed = 5; 42 private void
rmAction(int action) {
class Automobile {...}}
(b) Im
private int react(TrafficSignal 0;
static final int IDLE = signal) {
eger constants for static final int INCREASE_SPEED = 1;
private enumerated types.
switch(signal.getColor()) {
case TrafficSignal.RED: return STOP;
Figure 1. Running example: STOP = 3;
private static final int a hypothetical drive-by-w
case TrafficSignal.YELLOW:
private decide whether to stop or go
// static final int MAX_SPEED = 140;
/∗ The action (this.shouldGo()) performing, idle by default ∗/
if this automobile is currently
ch machinery.int currentAction = IDLE; example, in which
private return Third, INCREASE_SPEED;
the weak enum
/∗ The to manually enumerate initially 5 mph.language enum
ogrammercurrent speed of theSTOP; the
else return automobile, by ∗/
ts, whichcaseint currentSpeed = of // no changeAutomobile.
private TrafficSignal.GREEN:
increases the likelihood 5; and
return this.currentAction;
different enumint react(TrafficSignal signal) of these ne
private constants may be unin- ations {
default: throw new IllegalArgumentException
he same internal value. Finally, the
("Invalid traffic color");}}through compile-tim
switch(signal.getColor()) { // required
rittle public voidthe values {are com-
[?]:case TrafficSignal.YELLOW:
since drive() between the named
at compile time they are to stop or=go... ; ated values. It is als
TrafficSignal aSignal into
// decide whether inlined
new constants(this.shouldGo())
int if are added in between
reaction = this.react(aSignal); Action, whic
is an 37

int color = RED; 38 (reacti
INCREASE_SPEED ||
Accessor for the light’s current color ∗/
39 this.c
rmAction(reaction);}
40 Automobile this.
41
Action Enum
42 private void
Automobile { (b) Im
private static final int IDLE == 0;
static final int IDLE 0;
eger constants for static final int INCREASE_SPEED ==1;
enumerated types.
private static final int INCREASE_SPEED
private 1;
private static final int DECREASE_SPEED ==2;
private static final int DECREASE_SPEED 2;
Figure 1. Running example: STOP == 3;
private static final int STOP 3;
private static final int MAX_SPEED == 140;
private static final int MAX_SPEED 140;
/∗ The action this automobile is currently performing, idle by default ∗/
/∗ The action Third, the weak enumperforming, idle by default ∗/
this automobile is currently
private int currentAction = IDLE;
private
/∗ The current speed of the automobile,initially 55by language enum
ogrammercurrent speed of the automobile,the
/∗ The to manually enumerate initially mph. ∗/ mph. ∗/
private int currentSpeed = 5;
ts, which increases the likelihood of
private int currentSpeed = 5; and Automobile.
constants may be unin- ations
private int react(TrafficSignal signal) {{
private
he same internal value. Finally, the{
switch(signal.getColor()) through compile-tim
rittle [?]:case TrafficSignal.YELLOW:
case TrafficSignal.RED: return STOP; the named
since the values are com- between
at compile time they are to stop or go
// decide whether inlined into
// decide whether to stop or go
ated values. It is als
if are added in between is an Action, whic 37

INCREASE_SPEED ||
39 this.c
int getColor() {return this.color;}}40 this.
41
42 private void
Automobile { (b) Im
enumerated types.
private 1;
private
/∗ The to manually enumerate initially mph. Named-
ogrammercurrent speed of the automobile,the ∗/
mph. ∗/
private int currentSpeed = of
ts, which increases the likelihood 5;
private int currentSpeed = 5; Constant
and Automobile.
private

INCREASE_SPEED ||
39 this.c
41
42 private void
Automobile { (b) Im
enumerated types.
private 1;
private static final int MAX_SPEED Promising...
140;
private
private

INCREASE_SPEED ||
39 this.c
41
42 private void
Automobile { (b) Im
enumerated types.
private 1;
private
private not
Deﬁnitely
enumerizable

/∗ The action this color = RED; 38 (reacti
private int automobile is currently performing, idle by default */
/* idle by default ∗/
INCREASE_SPEED ||
/∗ Accessor Action currentAction = Action.IDLE; Client
Traffic Signal this.c
private intthe light’s current color ∗/IDLE; 39
for currentAction =
public intspeed of the automobile, initially 540
getColor() {return this.color;}} this.
/∗ The current
/*
rmAction(reaction);} mph. */
∗/
41
private int currentSpeed = 5; 42 private void
(b) Im
private int react(TrafficSignal 0; signal) {
static final int IDLE = signal) {
Action react(TrafficSignal
case TrafficSignal.RED: return Action.STOP;
STOP;
Figure 1. Running example: STOP = 3;
// static final int MAX_SPEED = 140;
/∗ The action (this.shouldGo()) performing, idle by default ∗/
if this automobile is currently
Third, INCREASE_SPEED;
the weak enum
private return Action.INCREASE_SPEED;
ogrammercurrent speed of theSTOP; the
automobile,
else return Action.STOP; by ∗/
ts, whichcaseint currentSpeed = of // no changeAutomobile.
increases the likelihood 5; and
private constants may be unin- ations {
("Invalid traffic color");}}through compile-tim
switch(signal.getColor()) { // required
rittle public voidthe values {are com-
since drive() between the named
at compile time they are to stop or=go... ; ated values. It is als
TrafficSignal aSignal into
// decide whether inlined
int if reactionthis.react(aSignal); Action, whic
Action are added in between
reaction = = this.react(aSignal);is an 38

My Approach to Refactoring to Enums

39


• Developed a semantics preserving, declarative
type inferencing algorithm that migrates legacy Java
code to use enums.

39


code to use enums.
• Algorithm:

39


code to use enums.
• Algorithm:
• Infers fields that are possibly being used to
simulate enumerated types.

39


code to use enums.
• Algorithm:
• Infers fields that are possibly being used to
simulate enumerated types.
• Identifies all code changes required to introduce
the inferred enum type.

39

Contributions

• Developed an open source Eclipse IDE plug-in called CONVERT
CONSTANTS TO ENUM that:
• Automatically refactors code to use enums.
• Provides a developer-friendly graphical user interface with
preview pane, constant selection, etc.
• Proposed as a Google Summer of Code (GSoC) project in
2009 and 2010.
• In progress to be included with the standard distribution of
Eclipse, proposed by IBM.

40

Contributions

• Developed an open source Eclipse IDE plug-in called CONVERT
CONSTANTS TO ENUM that:
• Automatically refactors code to use enums.
• Provides a developer-friendly graphical user interface with
preview pane, constant selection, etc.
• Proposed as a Google Summer of Code (GSoC) project in
2009 and 2010.
• In progress to be included with the standard distribution of
Eclipse, proposed by IBM.
• Evaluated plug-in on 17 open source applications:
• Analysis and transformation costs are practical.
• Enum-absence compensation patterns are widely used.
• Large percentage of fields can be automatically refactored. 40

α '%2"%,&)/ !)&-/ 1)!0#-
αctxt 30"+$5+ "$ 40"+0 α 1%. Enumerization Approach
#++(2
!"#$%& '( !)%*+,"-* .)/+/").(
function Enumerizable(C)P)
.',/&4$'& Enumerize(F,
R ← Enumerizable(F )
1: >AW ← C /* seed the worklist with the input constants */

2: QAN ← ∅ /* the non-enumerizable set ∩ Consistent(R) */
R ← U nique(R) ∩ Distinct(R) list, initially empty
3: GAfor all c T ∈ R 4,
5,' *22 ∈ C do
T ransf orm(T )
4: RA MakeSet(c) /* init the union-ﬁnd data structure */
?A &#4 5,'
5: end for

6: while W = ∅ do
!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(
7: /* remove an element from the worklist */
α ← e | ∈ %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+%
2)9%+!#2"$37 eM)W
8:

W ← W {α}
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&. -
9:

6)$-)$! 62#32%1 Contexts(α, P) do
10: for all αctxt ∈ )$!"!")*7 O0"* %**(16!"#$ +#(&- ,) "$'%
11: ¬isEnumerizableContext (α, αctxt ) then
-%!)-if!02#(30 !0) (*) #9 2)")+!"#$ %$- +(*!#1 +&%** &#%-)41

α '%2"%,&)/ !)&-/ 1)!0#-
#++(2
!"#$%& '( !)%*+,"-* .)/+/").(
Subset of static
final ﬁelds

5,' *22 ∈ C do
T ransf orm(T )
?A &#4 5,'
5: end for

6: while W = ∅ do
!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(
α ← e | ∈ %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+%
2)9%+!#2"$37 eM)W
8:

W ← W {α}
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&. -
9:

6)$-)$! 62#32%1 Contexts(α, P) do
10: for all αctxt ∈ )$!"!")*7 O0"* %**(16!"#$ +#(&- ,) "$'%
-%!)-if!02#(30 !0) (*) #9 2)")+!"#$ %$- +(*!#1 +&%** &#%-)41

α '%2"%,&)/ !)&-/ 1)!0#-
#++(2
!"#$%& '( !)%*+,"-* .)/+/").(
function Enumerizable(C)P) Abstract Syntax Tree (AST)

5,' *22 ∈ C do
T ransf orm(T )
?A &#4 5,'
5: end for

6: while W = ∅ do
!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(
α ← e | ∈ %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+%
2)9%+!#2"$37 eM)W
8:

W ← W {α}
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&. -
9:

6)$-)$! 62#32%1 Contexts(α, P) do
10: for all αctxt ∈ )$!"!")*7 O0"* %**(16!"#$ +#(&- ,) "$'%
-%!)-if!02#(30 !0) (*) #9 2)")+!"#$ %$- +(*!#1 +&%** &#%-)41

α '%2"%,&)/ !)&-/ 1)!0#-
#++(2
!"#$%& '( !)%*+,"-* .)/+/").(
Output: C /* seed the worklist with the input constants */
R←
1: >AW ← Enumerizable(F )

5,' *22 ∈ C do
T ransf orm(T )
?A &#4 5,'
5: end for

6: while W = ∅ do
!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(
α ← e | ∈ %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+%
2)9%+!#2"$37 eM)W
8:

W ← W {α}
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&. -
9:

6)$-)$! 62#32%1 Contexts(α, P) do
10: for all αctxt ∈ )$!"!")*7 O0"* %**(16!"#$ +#(&- ,) "$'%
-%!)-if!02#(30 !0) (*) #9 2)")+!"#$ %$- +(*!#1 +&%** &#%-)41

α '%2"%,&)/ !)&-/ 1)!0#-
#++(2
!"#$%& '( !)%*+,"-* .)/+/").(
R←

•2: QAN ← ∅U nique(R) ∩ Distinct(R) ∩ Consistent(R) */
Partitioning of program entities: list, initially empty
R ← /* the non-enumerizable set
5,' *22 ∈ C do
• Fields
T ransf orm(T )

5:
• end for declarations (return types)
?A Method
&#4 5,'
6:• while W = ∅ do (including formal parameters)
Local variables
!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(
α ← e | ∈ %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+%
2)9%+!#2"$37 eM)W
8:

W ← W {α}
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&. -
9:

6)$-)$! 62#32%1 Contexts(α, P) do
10: for all αctxt ∈ )$!"!")*7 O0"* %**(16!"#$ +#(&- ,) "$'%
-%!)-if!02#(30 !0) (*) #9 2)")+!"#$ %$- +(*!#1 +&%** &#%-)41

α '%2"%,&)/ !)&-/ 1)!0#-
#++(2
!"#$%& '( !)%*+,"-* .)/+/").(
R←

•2: QAN ← ∅U nique(R) ∩ Distinct(R) ∩ Consistent(R) */
Partitioning of program entities: list, initially empty
R ← /* the non-enumerizable set
5,' *22 ∈ C do
• Fields
T ransf orm(T )

5:
• end for declarations (return types)
?A Method
&#4 5,'
6:• while W = ∅ do (including formal parameters)
Local variables
!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(
/* remove an element from the worklist */
• Each partition contains elements that:
7:

α ← e | ∈ %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+%
2)9%+!#2"$37 eM)W
8:
• Transitively type-dependent upon one another
W ← W {α}
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&. -
9:

10:• Are all αctxt ∈ Contexts(α, P) do
6)$-)$!safe for enum type transformation +#(&- ,) "$'%
for 62#32%1 )$!"!")*7 O0"* %**(16!"#$
-%!)-if!02#(30 !0) (*) #9 2)")+!"#$ %$- +(*!#1 +&%** &#%-)
41

DECREASE_SPEED IDLE STOP

INCREASE_SPEED

GREEN
RED

YELLOW MAX_SPEED

42


INCREASE_SPEED

GREEN
RED

class
1 YELLOW TrafficSignal { MAX_SPEED
2 public enum Color {RED,
3 YELLOW,
4 GREEN};
5 /* Current color of the trafﬁc signal, initially red by default */
6 private Color color = Color.RED;
7 /* Accessor for the light’s current color */
8 public Color getColor() {return this.color;
9
42
10 class Automobile {


INCREASE_SPEED

GREEN
RED

color
class
1 YELLOW TrafficSignal { MAX_SPEED
3 YELLOW,
4 GREEN};
8 public Color getColor() {return this.color;
9
42


INCREASE_SPEED

GREEN
RED

1 class TrafficSignal color {
3 YELLOW,
YELLOW MAX_SPEED
4 GREEN};
8 public Color getColor() {return this.color;}}
9
1 private enum Action {IDLE,
42
2 INCREASE_SPEED,


INCREASE_SPEED

GREEN
RED

1 class TrafficSignal color {
3 YELLOW,
YELLOW MAX_SPEED
getColor
4 GREEN};
8 public Color getColor() {return this.color;}}
9
1 private enum Action {IDLE,
42
2 INCREASE_SPEED,

78 private int the light’s current color ∗/
/∗ Accessor for color = RED;
89 /∗ Accessorintthe light’s current {return this.color;}}
public for getColor() color ∗/
IDLE STOP
DECREASE_SPEED
910 public int getColor() {return this.color;}}
1112 class Automobile {final int IDLE = 0;
private static
1213 private static final int IDLE INCREASE_SPEED= 1;
1314 private static final int INCREASE_SPEED ==1;
GREENprivate static final int DECREASE_SPEED 2;
1415 private static RED
private staticfinal int DECREASE_SPEED = 2;
final int STOP = 3;
1516 private static final int STOP = 3; = 140;
private static final int MAX_SPEED
1617 private static final int MAX_SPEED = 140; defa
/∗ The action this automobile is currently performing, idle by
1718 private
color
/∗ The action int automobile is currently performing, idle by defaul
this currentAction = IDLE;
1819 private intspeed of the automobile, initially 5 mph. ∗/
/∗ The current currentAction = IDLE;
YELLOW MAX_SPEED
1920 /∗ The current speedgetColor
private int currentSpeed =initially 5 mph. ∗/
of the automobile, 5;
2021 private int currentSpeed = 5;
2122 private int react(TrafficSignal signal) {
2324 switch(signal.getColor()) {return STOP;
case TrafficSignal.RED:
2425 case TrafficSignal.RED: return STOP;
2526 case decide whether to stop or go
// TrafficSignal.YELLOW:
2627 // if (this.shouldGo())
decide whether to stop or go
2728 if (this.shouldGo())
return INCREASE_SPEED; 42

78 private int the light’s current color ∗/
/∗ Accessor for color = RED;
89 /∗ Accessorintthe light’s current {return this.color;}}
public for getColor() color ∗/
IDLE STOP
DECREASE_SPEED
910 public int getColor() {return this.color;}}
1112 class Automobile {final int IDLE = 0;
private static
1213 private static final int IDLE INCREASE_SPEED= 1;
YELLOW = 0;
1314 private static final int INCREASE_SPEED ==1;
GREENprivate static final int DECREASE_SPEED 2;
1415 private static RED
private staticfinal int DECREASE_SPEED = 2;
final int STOP = 3;
1516 private static final int STOP = 3; = 140;
private static final int MAX_SPEED
1617 private static final int MAX_SPEED = 140; defa
/∗ The action this automobile is currently performing, idle by
1718 private
color
/∗ The action int automobile is currently performing, idle by defaul
this currentAction = IDLE;
1819 private intspeed of the automobile, initially 5 mph. ∗/
/∗ The current currentAction = IDLE; MAX_SPEED
1920 /∗ The current speedgetColor
private int currentSpeed =initially 5 mph. ∗/
of the automobile, 5;
2324 switch(signal.getColor()) {return STOP;
2425 case TrafficSignal.RED: return STOP;
2526 case decide whether to stop or go
// TrafficSignal.YELLOW:
2627 // if (this.shouldGo())
decide whether to stop or go
2728 if (this.shouldGo())

7 13private int static = RED; int INCREASE_SPEED =
private color final
8 14 /∗ Accessor for the light’s current color ∗/ DECREASE_SPEED =
IDLE STOP
DECREASE_SPEED
9 15 public int getColor() {return this.color;}}
private static final int STOP = 3;
10 16 private static final int MAX_SPEED = 140;
11 class /∗ The action this automobile is currently performing, idle by d
17 Automobile {
12 18 private static final int IDLE = IDLE;
private int currentAction INCREASE_SPEED
YELLOW = 0;
13 19 private static final int INCREASE_SPEED = ∗/
GREEN /∗ The current speed of the automobile, initially 5 mph. 1;
14 20 private static RED
private int final int DECREASE_SPEED = 2;
currentSpeed = 5;
15 21 private static final int STOP = 3;
private int react(TrafficSignal signal) {
17 23
color
/∗ The action this automobile is currently performing, idle by defaul
18 24 private case currentAction = IDLE;
int TrafficSignal.RED: return STOP; MAX_SPEED
19 25 /∗ The current speedgetColor
case TrafficSignal.YELLOW: mph. ∗/
of the automobile, initially 5
20 26 private intdecide whether to stop or go
// currentSpeed = 5;
21 27 if (this.shouldGo())
22 28 private int return INCREASE_SPEED;
react(TrafficSignal signal) {
23 29 switch(signal.getColor()) {
else return STOP;
24 30 case TrafficSignal.RED: return no change
case TrafficSignal.GREEN: // STOP;
25 31 case TrafficSignal.YELLOW:
26 32 // decide whether to stop new IllegalArgumentExce
default: throw or go
27 33 if (this.shouldGo()) color");}} // required
("Invalid traffic 42

7 13private int static = RED; int INCREASE_SPEED =
private color final
8 14 /∗ Accessor for the light’s current color ∗/ DECREASE_SPEED =
IDLE STOP
DECREASE_SPEED
9 15 public int getColor() {return this.color;}}
11 class /∗ The action this automobile is currently performing, idle by d
17 Automobile {
12 18 private static final int IDLE = IDLE;
private int currentAction INCREASE_SPEED
YELLOW = 0;
13 19 private static final int INCREASE_SPEED = ∗/
/∗ The current speed of the automobile, initially 5 mph. 1;
14 20 private static RED
private int final int DECREASE_SPEED = 2;
currentSpeed = 5;
15 21 private static final int STOP = 3;
GREEN
17 23
color
/∗ The action this automobile is currently performing, idle by defaul
18 24 private case currentAction = IDLE;
int TrafficSignal.RED: return STOP; MAX_SPEED
19 25 /∗ The current speedgetColor
case TrafficSignal.YELLOW: mph. ∗/
of the automobile, initially 5
20 26 private intdecide whether to stop or go
// currentSpeed = 5;
21 27 if (this.shouldGo())
22 28 private int return INCREASE_SPEED;
react(TrafficSignal signal) {
23 29 switch(signal.getColor()) {
else return STOP;
24 30 case TrafficSignal.RED: return no change
case TrafficSignal.GREEN: // STOP;
25 31 case TrafficSignal.YELLOW:
26 32 // decide whether to stop new IllegalArgumentExce
default: throw or go
27 33 if (this.shouldGo()) color");}} // required
("Invalid traffic 42

2 public static final int RED = 0;
DECREASE_SPEED static final int RED_YELLOW = 1;
3 public IDLE STOP
4 public static final int YELLOW = 2;
5 public static final int GREEN = 3;
6 /∗ Current color of the trafﬁc signal, initially red by default ∗/
YELLOW = RED; INCREASE_SPEED
7 private int color
8 /∗ Accessor for the light’s current color ∗/
9 RED
10
GREEN color
12 private static final int IDLE = 0;
13 private static final int INCREASE_SPEED = 1 MAX_SPEED
getColor
14 private static final int DECREASE_SPEED = 2
15 private static final int STOP = 3;
16 private static final int MAX_SPEED = 140;
17 /∗ The action this automobile is currently performing, idle by de
18 private int currentAction = IDLE;
19 /∗ The current speed of the automobile, initially 5 mph. ∗/
21
42

2 public static final int RED = 0;
DECREASE_SPEED static final int RED_YELLOW = 1;
3 public IDLE currentAction STOP
4 public static final int YELLOW = 2;
5 public static final int GREEN = 3;
6 /∗ Current color of the trafﬁc signal, initially red by default ∗/
YELLOW = RED; INCREASE_SPEED
7 private int color
8 /∗ Accessor for the light’s current color ∗/
9 RED
10
GREEN color
12 private static final int IDLE = 0;
13 private static final int INCREASE_SPEED = 1 MAX_SPEED
getColor
14 private static final int DECREASE_SPEED = 2
15 private static final int STOP = 3;
16 private static final int MAX_SPEED = 140;
17 /∗ The action this automobile is currently performing, idle by de
18 private int currentAction = IDLE;
19 /∗ The current speed of the automobile, initially 5 mph. ∗/
21
42

l RED;
signal) { 23
25 case TrafficSignal.RE
public int getColor() {return this.color;}} privateorC // decide whether to stop
6
turn STOP;
7class Automobile color = RED;
private int { 22 switch(signal.getColor(
24
26 7 /* Accessor f
case (this.shouldGo()
if TrafficSignal.YE
urrent colorAccessor for thefinal currentIDLE ∗/ 0; // decide whether to stop or
8 /∗ ∗/
private static light’s int color currentAction
23
IDLE
25 = casereturn Action.INC
TrafficSignal.RE
STOP
turnDECREASE_SPEED{
STOP;
lass Automobile 27 8 public Co
() private static final int {return case (this.shouldGo()
{return this.color;}} 24
9 private static final int 26 INCREASE_SPEED = 1; Action.
public int getColor()28 if TrafficSignal.YE
this.color;}}
IDLE = 0; else return to stop or
25
9
// decide whether
10 private static final int 27 DECREASE_SPEED = 2;
private static final int 29 casereturn Action.INC
TrafficSignal.GR
class Autom
INCREASE_SPEED(this.shouldGo()
10 = 1;
// no private static final int STOP = 3; if
change 26 else return Action.
11 private static final int 28
class Automobile { 30 return this.current
n; int IDLE = 0;
l private static final int 27 return private e
DECREASE_SPEED = 2; Action.INC
11
INCREASE_SPEED
private static final 31
// no change
ArgumentException
YELLOW
12 private static final int 29 MAX_SPEED 0; 12int IDLE case TrafficSignal.GR
= 140;
STOP = 3; default: throwAction.
= else return INCREAS new Il
l intThe action this automobile 1; 28
13 private static final= int 32
INCREASE_SPEED
/∗ //private static final 30 return this.current
is currentlyINCREASE_SPEEDdefault ∗/
int performing, idle by =traffic c
("Invalid 1;
n;
);}} required MAX_SPEED case 13
29 = 140; throw new Il
default: DECREAS
TrafficSignal.GR
14 /∗ Theprivate automobile = currently = DECREASE_SPEED = 2;
l int DECREASE_SPEED final 31
ArgumentException static is 2; 33 performing, returndefault ∗/
// no private int currentAction
change
action this 3; RED int IDLE; idle by this.current
30 14 STOP};
n; intThe current static final 34
l /∗ required =
STOP 32 ("Invalid traffic c
15 private int speed of the automobile, initially default:drive()new Il
);}} //private currentAction31= IDLE; = mph. ∗/ throw {
public void
int STOP 5 3; 15 private s
33
16 /∗ Theprivate GREEN 140; color initially 5 mph. ∗/ = 140;traffic c
ArgumentException =
l int MAX_SPEEDcurrentSpeed = 5; TrafficSignal aSignal =
static final 35
private int of the automobile, int MAX_SPEED 16 drive() {
; current speed
);}} ///∗ The action this automobile is ∗/
required
32
34 public("Invalid /* The this.
void action
17 private performing, idle by defaultcurrently performing, idle by default ∗/ A
e is currently 36 Action reaction =
ignal);
Action && IDLE;
= int currentSpeed 33 5; =
35
37
; private int react(TrafficSignal signal) drive() { if (reaction private =
17
TrafficSignal!= this.cu
aSignal
Actionprivate int currentAction = IDLE;void { /* The this.
public
(reaction != curren
18 34
36 Action 18 MAX_SPEED=Action
reaction
automobile,The currentmph. ∗/ the automobile, initially 5 mph. ∗/ aSignal =
EED ||/∗ initially 5 speed of
ignal); 38
getColor
switch(signal.getColor()) { TrafficSignal!= this.cu
19 private int react(TrafficSignal signal) { 35
; 37
39 if (reaction private i
19
this.currentSpeed
X_SPEED))5; TrafficSignal.RED: = 5;
Speed =case
Actionprivate int currentSpeed return STOP;
20 && 36 Action 20
(reaction !==Action
reaction this.
EED switch(signal.getColor()) {
ignal); 38
40 this.performActio
21
|| case TrafficSignal.YELLOW: if (reaction != this.cu
ction);} 37
Action && TrafficSignal.RED: return STOP;
case 39
41 this.currentSpeedA
21 private
X_SPEED)) // decide whether to stop or go
rafficSignal signal) {
22
EED || private int react(TrafficSignal (reaction{!= Action
38
40 signal)
case{ TrafficSignal.YELLOW: privatethis.currentSpeed
22 switch(
void performActio
ction);} {...}}
Color()) if (this.shouldGo())
23action)// decide whether to stop or go
X_SPEED)) switch(signal.getColor()) { 39
41 (b) Improvements afte
23 case
nal.RED: return STOP;
ction);}if case TrafficSignal.RED:
24 (this.shouldGo())
40
42 private this.performActio
return INCREASE_SPEED; return 24STOP; void performActiocase
oraction) {...}}
enumerated types.
nal.YELLOW: (b) Improvements // de
afte
25 else return STOP; 41
return INCREASE_SPEED; private void performActio
25
o stop or gocase //TrafficSignal.GREEN: // no change
oraction)else return STOP; stop or go
26 enumerated types.
{...}} decide whether to
42
if
ldGo()) example: a hypothetical drive-by-wire applica
unning return this.currentAction; (b) Improvements afte 26
27 if (this.shouldGo())// no change 27
case TrafficSignal.GREEN:
42
r

l RED;
signal) { 23
6
turn STOP;
24
26 7 /* Accessor f
if TrafficSignal.YE
8 /∗ ∗/
23
IDLE
TrafficSignal.RE
turnDECREASE_SPEED{
lass STOP; this.color;}} 27
Automobile 8 public Co
{return int getColor()24
public if TrafficSignal.YE
this.color;}}
28 9
private static final int 27 DECREASE_SPEED whether
25 // decide STOP
casereturn 2; Action.INC
10 private static final int 29 INCREASE_SPEED 10 = =
TrafficSignal.GR
class Autom
1;
// no private static final int STOP = 3; if (this.shouldGo()
n; int IDLE = 0;
11
INCREASE_SPEED
// no change
ArgumentException
YELLOW
= 140;
INCREASE_SPEED
("Invalid 1;
n;
);}} required MAX_SPEED case 13
29 = 140; throw new Il
default: DECREAS
TrafficSignal.GR
ArgumentException static is 2; 33 performing, returndefault ∗/
change
30 14 STOP};
l /∗ required =
public void
33
ArgumentException =
static final 35
; current speed
required
32
void action
ignal);
Action && IDLE;
35
37
17
aSignal
public
(reaction != curren
18 34
reaction
ignal); 38
getColor
; 37
19
this.currentSpeed
Speed =case
20 && 36 Action 20
(reaction !==Action
reaction this.
ignal); 38
21
ction);} 37
case 39
21 private
22
38
40 signal)
22 switch(
void performActio
ction);} {...}}
23 case
40
oraction) {...}}
enumerated types.
afte
25
42
if
42
r

l RED;
signal) { 23
6
turn STOP;
24
26 7 /* Accessor f
if TrafficSignal.YE
8 /∗ ∗/
23
IDLE
TrafficSignal.RE
turnDECREASE_SPEED{
Automobile 8 public Co
this.color;}}
28 9
25 // decide STOP
TrafficSignal.GR
class Autom
1;
n; int IDLE = 0;
11
INCREASE_SPEED
// no change
ArgumentException
YELLOW
= 140;
INCREASE_SPEED
("Invalid 1;
n;
);}} required MAX_SPEED case 13 react DECREAS
29 = 140; TrafficSignal.GR
default: throw new Il
static is 2; 30 performing, returndefault ∗/
change 31
ArgumentException
14 STOP};
l /∗ required =
public void
33
ArgumentException =
static final 35
; current speed
required
32
void action
ignal);
Action && IDLE;
35
37
17
aSignal
public
(reaction != curren
18 34
reaction
ignal); 38
getColor
; 37
19
this.currentSpeed
Speed =case
20 && 36 Action 20
(reaction !==Action
reaction this.
ignal); 38
21
ction);} 37
case 39
21 private
22
38
40 signal)
22 switch(
void performActio
ction);} {...}}
23 case
40
oraction) {...}}
enumerated types.
afte
25
42
if
42
r

l RED;
signal) { 23
6
turn STOP;
24
26 7 /* Accessor f
if TrafficSignal.YE
8 /∗ ∗/
private static light’s int color = casereturn Action.INC
23
25 TrafficSignal.RE
turnDECREASE_SPEED{
Automobile 8 IDLEpublic Co
this.color;}}
28 9
25 // decide STOP
TrafficSignal.GR
class Autom
1;
n; int IDLE = 0;
11
INCREASE_SPEED
// no change
ArgumentException
YELLOW int IDLE case TrafficSignal.GR
12 private static final int 29 MAX_SPEED 0; 12 = 140;
INCREASE_SPEED
("Invalid 1;
n;
);}} required MAX_SPEED case 13 react DECREAS
29 = 140; TrafficSignal.GR
default: throw new Il
static is 2; 30 performing, returndefault ∗/
change 31
ArgumentException
14 STOP};
l /∗ required =
public void
int STOP 5 3; 15currentAction
private s
33
ArgumentException =
static final 35
; current speed
required
32
void action
ignal);
Action && IDLE;
35
37
17
aSignal
public
(reaction != curren
18 34
reaction
ignal); 38
getColor
19 private int react(TrafficSignal signal) {35
; 37
19
this.currentSpeed
Speed =case
20 && 36 Action 20
(reaction !==Action
reaction this.
ignal); 38
21
ction);} 37
case 39
21 private
22
38
40 signal)
22 switch(
void performActio
ction);} {...}}
23 case
40
oraction) {...}}
enumerated types.
afte
25
42
if
42
r

Identifiers Array access/creation expressions
Identifiers Conditional expressions Identifiers Array access/creation expressions
Identifiers Conditional expressions function XA(α,ID) function XA(α, E XP1 [E XP2 ])
function EA(α,ID) function EA(α, E XP1 ? E XP2 : E XP3 ) function XA(α,ID) function XA(α, E XP1 [E XP2 ])
function EA(α,ID) function EA(α, E XP1 ? E XP2 : E XP3 ) return XA(α, P arent(ID))
1:
1: return EA(α, P arent(ID)) 1: return XA(α, P arent(ID)) 1: if contains(E XP2 , α) then
1: if contains(E XP2 , α) ∨ contains (E XP3 , α) then 1: if contains(E XP2 , α) then
1: return EA(α, P arent(ID)) 1: if contains(E XP2 , α) ∨ contains (E XP3 , α) then
Parenthesized expressions
Parenthesized expressions return EA(α, P arent(E XP1 ? E XP2 : E XP3 )) Parenthesized expressions 2: return ∅
Parenthesized expressions
2:
return EA(α, P arent(E XP1 ? E XP2 : XA(α,(ID)) 2: return ∅
2: function E XP3 )) 3: else
function EA(α,(ID)) 3: else function XA(α,(ID)) 3: else
function EA(α,(ID)) 3: else
1: return XA(α, P arent(ID)) 4: return XA(α, P arent(E XP1 ))
1: return EA(α, P arent(ID)) 4: return true 1: return XA(α, P arent(ID)) 4: return XA(α, P arent(E XP1 ))
1: return EA(α, P arent(ID)) 4: return true 5: end if
5: end if Cast expressions 5: end if
Cast expressions 5: end if Cast expressions
Cast expressions Array access/creation expressions function XA(α, (T YPE)E XP) Array initialization expressions
function EA(α, (T YPE)E XP) Array access/creation expressions function XA(α, (T YPE)E XP) Array initialization expressions
function EA(α, (T YPE)E XP) function EA(α, E XP1 [E XP2 ]) 1: return ∅
function XA(α, {E XP1 , . . . , E XPn })
1: return false function EA(α, E XP1 [E XP2 ]) 1: return ∅
function XA(α, {E XP1 , . . . , E XPn })
1: return false
Field access expressions 1: R ← ∅
1: if contains(E XP2 , α) then 1: R ← ∅
Field access expressions 1: if contains(E XP2 , α) then Field access expressions 2: for E XPi , 1 ≤ i ≤ n do
Field access expressions 2: return false function XA(α, E XP.ID) 2: for E XPi , 1 ≤ i ≤ n do
function EA(α, E XP.ID) 2: return false function XA(α, E XP.ID) R ← R ∪ XD(E XPi )
function EA(α, E XP.ID) 3: else 1: return XA(α, P arent(E XP))
3:
3: R ← R ∪ XD(E XPi )
1: return EA(α, P arent(E XP)) 3: else 1: return XA(α, P arent(E XP)) 4: end for
1: return EA(α, P arent(E XP)) return EA(α, P arent(E XP1 )) 4: end for
4:
return EA(α, P arent(E XP1 )) Assignment expressions 5: return R
Assignment expressions 5: end if
4: Assignment expressions
Assignment expressions function XA(α,E XP1 = E XP2 ) 5: return R
function EA(α,E XP1 = E XP2 ) 5: end if function XA(α,E XP1 = E XP2 )
function EA(α,E XP1 = E XP2 ) Array initialization expressions Return statements
Array initialization expressions 1: return XD(E XP1 ) ∪ XD(E XP2 ) Return statements
1: return ED(E XP1 ) ∧ ED(E XP2 )
function EA(α, {E XP1 , . . . , E XPn }) 1: return XD(E XP1 ) ∪ XD(E XP2 ) function XA(α,return E XP)
1: return ED(E XP1 ) ∧ ED(E XP2 )
Subtract assignment expressions
function EA(α, {E XP1 , . . . , E XPn }) function XA(α,return E XP)
Subtract assignment expressions Subtract assignment expressions 1: return XD(M ethodDecl(return E XP ))
Subtract assignment expressions 1: let ie = true function XA(α,E XP1 -= E XP2 ) 1: return XD(M ethodDecl(return E XP ))
function EA(α,E XP1 -= E XP2 ) 1: let ie = true function XA(α,E XP1 -= E XP2 )
function EA(α,E XP1 -= E XP2 ) 2: for E XPi , 1 ≤ i ≤ n do Method declaration statements
2: for E XPi , 1 ≤ i ≤ n do 1: return ∅ Method declaration statements
1: return false 3: ie ← ie ∧ ED(E XPi ) 1: return ∅ function XA(α,ID(P 1 , . . . ,P n ))
1: return false 3: ie ← ie ∧ ED(E XPi ) Divide assignment expressions function XA(α,ID(P 1 , . . . ,P n ))
Divide assignment expressions 4: end for Divide assignment expressions 1: R ← ∅
Divide assignment expressions 4: end for function XA(α,E XP1 /= E XP2 ) 1: R ← ∅
function EA(α,E XP1 /= E XP2 ) 5: return ie function XA(α,E XP1 /= E XP2 ) 2: for all return E XPr ∈ returnStmts(ID(P 1, . . . , P n )) do
function EA(α,E XP1 /= E XP2 ) 5: return ie 2: for all return E XPr ∈ returnStmts(ID(P 1, . . . , P n )) do
1: return ∅ R ← R ∪ XD(E XPr )
1: return false Return statements 1: return ∅ 3:
R ← R ∪ XD(E XPr )
1: return false Return statements Infix addition expressions
3:
function EA(α,return E XP) 4: end for
Infix addition expressions function EA(α,return E XP) Infix addition expressions 4: end for
Infix addition expressions function XA(α,E XP1 + E XP2 ) 5: return R
function EA(α,E XP1 + E XP2 ) 1: return true function XA(α,E XP1 + E XP2 ) 5: return R
function EA(α,E XP1 + E XP2 ) 1: return true 1: return ∅ Formal parameters
1: return false Method declaration statements 1: return ∅ Formal parameters
1: return false Method declaration statements Infix multiplication expressions function XA(α,P i )
function EA(α,ID(P 1 , . . . ,P n )) function XA(α,P i )
Infix multiplication expressions
Infix multiplication expressions function EA(α,ID(P 1 , . . . ,P n )) function XA(α,Emultiplication expressions
Infix
XP1 * E XP2 ) 1: R ← ∅
function EA(α,E XP1 * E XP2 ) 1: let re = true function XA(α,E XP1 * E XP2 ) 1: R ← ∅
function EA(α,E XP1 * E XP2 ) 1: let re = true 1: return ∅ 2: /*extract the ith argument of each invocation of the declaring
1: return false 2: for all return E XPr ∈ returnStmts(ID(P 1, . . . , P n )) do 1: return ∅ 2: /*extract the ith argument of each invocation of the declaring
1: return false 2: for all return E XPr ∈ returnStmts(ID(P 1, . . . , P n )) do method*/
3: re ← re ∧ ED(E XPr ) Prefix unary minus expressions method*/
Prefix unary minus expressions 3: re ← re ∧ ED(E XPr ) Prefix unary minus expressions 3: let α = M ethodDecl(P i )
ˆ
Prefix unary minus expressions 4: end for function XA(α,-E XP) 3: let α = M ethodDecl(P i )
ˆ
function EA(α,-E XP) 4: end for function XA(α,-E XP) 4: for all αctxt ∈ Invocations(α, P) do
ˆ ˆ
function EA(α,-E XP) 5: return re 1: return ∅ 4: for all αctxt ∈ Invocations(α, P) do
ˆ ˆ
1: return false 5: return re 1: return ∅ 5: R ← R ∪ XD(Arg(αctxt, i)) ˆ
1: return false Formal parameters R ← R ∪ XD(Arg(αctxt, i))
ˆ
Postfix increment expressions 5:
Postfix increment expressions Formal parameters Postfix increment expressions 6: end for
Postfix increment expressions function EA(α,P i ) function XA(α,E XP ++) 6: end for
function EA(α,E XP ++) function EA(α,P i ) function XA(α,E XP ++) 7: return R
function EA(α,E XP ++) 7: return R
1: let ae = true 1: return ∅
1: return false 1: let ae = true 1: return ∅ Method invocation expressions
1: return false 2: /*check the ith argument of each invocation of the declaring
Equality expressions Method invocation expressions
Equality expressions 2: /*check the ith argument of each invocation of the declaring
Equality expressions function XA(α,ID(E XP1 , . . . , E XPn ))
Equality expressions method*/ function XA(α,E XP1 == E XP2 ) function XA(α,ID(E XP1 , . . . , E XPn ))
function EA(α,E XP1 == E XP2 ) method*/ function XA(α,E XP1 == E XP2 ) 1: R ← ∅
function EA(α,E XP1 == E XP2 ) 3: let α = M ethodDecl(P i )
ˆ 1: R ← ∅
3: let α = M ethodDecl(P i )
ˆ 1: return XD(E XP2 ) ∪ XD(E XP1 ) 2: for E XPi , 1 ≤ i ≤ n do
1: return ED(E XP1 ) ∧ ED(E XP2 ) 4: for all αctxt ∈ Invocations(α, P) do
ˆ ˆ 1: return XD(E XP2 ) ∪ XD(E XP1 ) 2: for E XPi , 1 ≤ i ≤ n do
1: return ED(E XP1 ) ∧ ED(E XP2 ) 4: for all αctxt ∈ Invocations(α,Inequality expressions
ˆ ˆ P) do
Inequality expressions Inequality expressions 3: if contains(E XPi , α) then
Inequality expressions 5: ae ← ae ∧ ED(Arg(αctxt, i))
ˆ 3: if contains(E XPi , α) then
5: ae ← ae ∧ ED(Arg(αctxt, i))function XA(α,E XP1 != E XP2 )
ˆ 4: R ← R ∪ XD(E XP1 )
function EA(α,E XP1 != E XP2 ) 6: end for function XA(α,E XP1 != E XP2 ) 4: R ← R ∪ XD(E XP1 )
function EA(α,E XP1 != E XP2 ) 6: end for 1: return XD(E XP1 ) ∪ XD(E XP2 ) 5: end if
1: return ED(E XP1 ) ∧ ED(E XP2 ) 7: return ae 1: return XD(E XP1 ) ∪ XD(E XP2 ) 5: end if
1: return ED(E XP1 ) ∧ ED(E XP2 ) 7: return ae 6: end for
Method invocation expressions Switch statements 6: end for
Switch statements Method invocation expressions Switch statements 7: if R = ∅ then
Switch statements function XA(α, switch(E XP)) 7: if R = ∅ then
function EA(α, switch(E EA(α, switch(E XP))
XP)) function EA(α,ID(E XP1 , . . . , E XPn )) function XA(α, switch(E XP))
function function EA(α,ID(E XP1 , . . . , E XPn )) R ← XD(E XP) 8: return R
1: for E XPi , 1 ≤ i ≤ n do
1:
1: R ← XD(E XP)
8: return R
1: let se = ED(E XP) 9: else
1: let se = ED(E XP) 1: for E XPi , 1 ≤ i ≤ n do 2: for all case E XP c ∈ cases(switch(E XP )) do 9: else
2: let ce = true 2: if contains(E XPiif α) then
, contains(E XP , α) then 2: for all case E XP c ∈ cases(switch(E XP )) do 10: return XA(α, P arent(ID(E XP1 , . . . , E XPn )))
2: let ce = true 2: i 3: R ← XD(E XPc ) 10: return XA(α, P arent(ID(E XP1 , . . . , E XPn )))
3: for all case E XP c ∈ cases(switch(E XP )) do 3: return true3: return true 3: R ← XD(E XPc ) 11: end if
3: for all case E XP c ∈ cases(switch(E XP )) do 4: end for 11: end if
4: ce ← ce ∧ ED(Ece ← ce ∧ ED(E XP )
XPc ) 4: end if end if 4: end for
4: c 4: 5: return R General statements
5: end for 5: end for 5: return R General statements
5: end for 5: end for function XA(α,S MT )
6: return se ∧ ce 6: return EA(α, P arent(ID(E XP1 , . . . , E XPn ))) Switch case statements function XA(α,S MT )
6: return se ∧ ce 6: return EA(α, P arent(ID(E XP1 , . . . , E XPnSwitch case statements
))) 1: R ← ∅
General statements function XA(α,case E XP) 1: R ← ∅
Switch case statements case statements General statements function XA(α,case E XP) 2: for E XP ∈ Children(S MT) do
Switch 1: return XA(α, switchStmt(case E XP )) 2: for E XP ∈ Children(S MT) do
function EA(α,case E XP) EA(α,case E XP) function XA(α,Sfunction XA(α,S MT )
MT ) 1: return XA(α, switchStmt(case E XP ))
function 3: R ← R ∪ XD(E XP)
1: return EA(α, switchStmt(case E XP )) 1: let se = true Conditional expressions 3: R ← R ∪ XD(E XP)
1: let se = true Conditional expressions 4: end for
1: return EA(α, switchStmt(case E XP )) 4: end for
2: for E XP ∈ Children(S MT) do function XA(α, E XP1 ? E XP2 : E XP3 )
2: for E XP ∈ Children(S MT) do function XA(α, E XP1 ? E XP2 : E XP3 ) 5: return R
1: if contains(E XP2 , α) ∨ contains (E XP3 , α) then 5: return R
3: se ← se ∨ED(E XP)← se ∨ED(E XP)
se
3: 1: if contains(E XP2 , α) ∨ contains (E XP3 , α) then
4: end for 2: return XA(α, P arent(E XP1 ? E XP2 : E XP3 ))
4: end for 2: return XA(α, P arent(E XP1 ? E XP2 : E XP3 ))
5: return se 3: else
5: return se 3: else
4: return ∅
Figure 7. EnumerizableEnumerizable ascender. return ∅
Figure 7. ascender.
4:
5: end if 12 12
5: end if
10 10 Figure 9. Extraction ascender.
Figure 9. Extraction ascender.
43

private int color = RED; 38 (reacti
INCREASE_SPEED ||
/∗ Accessor for the light’s current or go ∗/ Enums vs. Constants
// decide whether toDistinction:
Algorithmic stop color
39 this.c
publicif (this.shouldGo())
int getColor() {return this.color;}} 40 this.

else return STOP; 42 private void
casestatic final int IDLE = no change
TrafficSignal.GREEN: // 0; (b) Im
private
Figure 1. Running example:color");}} // required
("Invalid traffic a hypothetical drive-by-w
public void drive() is currently performing, idle by default ∗/
/∗ The action this automobile {
TrafficSignal the weak enum ;
private Third, aSignal = ...
int reaction = this.react(aSignal); ∗/ by
if (reaction != this.currentAction &&
ts, which increases the likelihood 5;
private int currentSpeed = of
(reaction != INCREASE_SPEED ||
and Automobile.
privatethis.currentSpeed unin-
constants may be <= MAX_SPEED)) {
ations
this.performAction(reaction);}
switch(signal.getColor()) { through compile-tim
rittle private void performAction(int action) {...}}named
since the values are com- between the
// decide whether inlined into ated values. It is als
new constants if(a)are added in constants for enumerated types., whic
Using integer
(this.shouldGo()) between is an Action 44

class Automobile {
38 (reacti
INCREASE_SPEED ||
/∗ Accessor static final int go ∗/ Enums vs. Constants
private
Algorithmic Distinction: = 0;
// decide whether current or
for the light’s to stop color
tSpeed <= MAX_SPEED)) IDLE
39 this.c
publicif static final int INCREASE_SPEED = 1; this.
(this.shouldGo()) 40
private
private static final int DECREASE_SPEED = 2; void 42 private
else return STOP;
class Automobile {...}} int STOP = 3;
private static final (b) Im
casestatic final int IDLE = no change
TrafficSignal.GREEN: // 0;
private return this.currentAction;
private int currentAction = IDLE; // required
Figure 1. current speed oftraffic color");}} mph. ∗/ drive-by-w
private static example: STOP = 3;
/∗ The
Running final int a hypothetical
("Invalid
the automobile, initially 5
privatevoid drive() {
public int currentSpeed = 5;
TrafficSignal the weak enum ;
private Third, aSignal = ...
ogrammercurrent speed of the automobile,the{ 5 mph.language enum
/∗ The to manually enumerate initially by ∗/
int reaction = this.react(aSignal);
switch(signal.getColor())
ts, whichcaseint currentSpeed = ofreturn STOP;
privateincreases the likelihood 5;
TrafficSignal.RED:
and Automobile.
case constants may be unin-
private TrafficSignal.YELLOW:
this.currentSpeed <= MAX_SPEED)) { ations
// decide whether to stop or go {
this.performAction(reaction);}
if (this.shouldGo())
through compile-tim
[?]:case returnvalues are com-
since the INCREASE_SPEED; between the
TrafficSignal.YELLOW:
// decide whether STOP; into
else return inlined ated values. It is als
if(a)are added in constants for enumerated types., whic
Using integer
TrafficSignal.GREEN: // no change
case (this.shouldGo())
new constants between is an Action 44

class Automobile {
38 (reacti
INCREASE_SPEED ||
/∗ Accessor static final int go ∗/ Enums vs. Constants
private
// decide whether toDistinction:
Algorithmiccurrentcolor ∗/
Accessor for the light’s current or IDLE = 0;
for the light’s stop color
39 this.c
publicif static final int INCREASE_SPEED = 1; this.
(this.shouldGo())
public int getColor() {return this.color;}} 40
private
private static final int DECREASE_SPEED = 2; void 42 private
else return STOP;
Automobile final
rmAction(int action) { {
class Automobile {...}} int STOP = 3;
private static (b) Im
casestatic final int IDLE ==no change
private static final int IDLE
private static final int MAX_SPEED = 140; 0;
private static final isint INCREASE_SPEED by default ∗/
private this automobile currently performing, idle 1;
/∗ The action
private int currentActionDECREASE_SPEED
private static final int = IDLE; // required 2;
private static example: STOP == 3;
private static final int a hypothetical
/∗ The
Running final int STOP 3;
("Invalid
the automobile, initially 5
private int currentSpeed MAX_SPEED
privatevoid drive() { int = 5;
public
static final 140;
/∗ The action this automobile is currently performing, idle by default ∗/∗/
action Third, the weak enumperforming, idle by in which
this automobile is currently default
ch machinery.int currentAction == IDLE; example,
private int currentAction ... ;
TrafficSignal aSignal =
private int react(TrafficSignal signal) { IDLE;
private
ogrammercurrent speed of the automobile,the{ 55mph.language enum
/∗ The current speed of the automobile,initially by ∗/
/∗ The to manually enumerate initially mph. ∗/
int reaction = this.react(aSignal);
ts, whichcaseint currentSpeed == ofreturn STOP;
private int currentSpeed 5;
increases the likelihood
private TrafficSignal.RED:5;
and Automobile.
case constants may be unin-
this.currentSpeed <= MAX_SPEED)) {{
private int react(TrafficSignal signal)
ations
// this.performAction(reaction);}
through compile-tim
[?]:case returnvalues are com-return STOP; the
since the INCREASE_SPEED; between
at compile time return to stop or go
else they are to stop or go
// decide whether inlined ated values. It is als
if(a)are added in constants for enumerated types., whic
Using integer
TrafficSignal.GREEN: // no change
new constants (this.shouldGo())
if between is an Action 44

class Automobile {
38 (reacti
INCREASE_SPEED ||
class Automobile final int go ∗/ Enums vs. Constants
Accessor for the light’s toDistinction:
private
Algorithmic stop color
/∗ Accessor static { current or IDLE = 0;
// decide whether currentcolor ∗/
for the light’s
39 this.c
publicif static final int IDLE this.color;}}1; this.
(this.shouldGo())
public int getColor() int INCREASE_SPEED =40
private static
rmAction(reaction);} final
private {return = 0;
private static final int INCREASE_SPEED = 1; void
private static final int DECREASE_SPEED = 2; 42 private
else return STOP;
Automobile final
rmAction(int action) { {
class Automobile {...}} int DECREASE_SPEED = 2;

?
private static (b) Im
casestatic final int IDLE ==no change
private static final int IDLE
3;
private enumerated types. MAX_SPEED = 140;
private static final isint INCREASE_SPEED by default ∗/
private this automobile currently performing, idle
MAX_SPEED = 140; 1;
/∗ The action
default: throw new currently performing, idle
/∗ The action this automobile int IllegalArgumentException
private static final isint DECREASE_SPEED ==2;
private int currentActionDECREASE_SPEED by default ∗/
static final
private = IDLE; // required 2;
private static example: STOPIDLE;
Running final int a =initially3;
("Invalid final int hypothetical
private int currentActionSTOP == 3;
/∗ The static the automobile, 5
private static of the automobile, initially 5 mph.140;
private int currentSpeed MAX_SPEED == 140;
/∗ The current speed final int MAX_SPEED
privatevoid drive() { int = 5;
static final
public int automobile is currently5;
∗/
/∗ The action this currentSpeed = performing, idle by default ∗/∗/
private Third, the weak enumperforming, idle by in which
action this automobile is currently default
private int react(TrafficSignal signal) { IDLE;
private
ogrammercurrent speed of the automobile,the{ 5signal) {
/∗ The to manually enumerate initially mph. ∗/
int reaction = this.react(aSignal); ∗/
private int react(TrafficSignal
switch(signal.getColor()) mph.
ts, whichcaseint currentSpeed == ofreturn STOP;
private int currentSpeed 5;{
increases the likelihood
private TrafficSignal.RED:5;
and Automobile.
case constants may be unin-return STOP; these ne
TrafficSignal.RED:
different enum int react(TrafficSignal signal){{
caseint react(TrafficSignal signal) of
TrafficSignal.YELLOW: ations
this.currentSpeed <= MAX_SPEED))
case
he same internal value. to stop or go {{
// decide whether Finally, the
through compile-tim
casereturn INCREASE_SPEED;
at compile time return to stop or go
inlined
// decide whether STOP; ated values. It is als
else Using integer constants for enumerated types.
(a) return
if TrafficSignal.GREEN: // nois an Action, whic
case (this.shouldGo()) change
if are added in between 44

this.currentAction && {
class case int color = RED;
Automobile
class Automobile {
INCREASE_SPEED ||
38 (reacti
private decide whether toDistinction: Enums vs. Constants
static final int IDLE = 0;
// Algorithmiccurrentor go ∗/
Accessor for the light’s stop color
for the light’s this.c
/∗ Accessor static { current color ∗/
class Automobile final int IDLE = 0;
private static
39
tSpeed <= MAX_SPEED)) final int INCREASE_SPEED = 1;
privateint getColor() {return this.color;}} this.
publicif static final int IDLE this.color;}}1;
(this.shouldGo())
public int getColor() int INCREASE_SPEED =
{return = 0;
rmAction(reaction);} final int DECREASE_SPEED = 2;
private static
private return INCREASE_SPEED; 41
private static { STOP; final int STOP = 3; 42 private
else return
Automobile {
class Automobile final int STOP = 3;

?
rmAction(int action) {...}} int DECREASE_SPEED = 2;
private static final
private static final int IDLE ==no change
static
case static final int IDLE // 0;
TrafficSignal.GREEN: (b) Im
private static final int STOP
private 0;
3;
private enumerated types. currently performing, idle by default ∗/
MAX_SPEED = 140;
eger constantsaction this automobile isint INCREASE_SPEED ==1;
/∗ The for static final int INCREASE_SPEED
private static final is currently performing, idle by default ∗/
private this automobile MAX_SPEED = 140; 1;
/∗ The action
private static final int DECREASE_SPEED
default: currentAction = IDLE;
int throw new IllegalArgumentException
private int currentAction = IDLE; 2;
/∗ The action this automobile currently performing, idle by default ∗/
private
private static of the automobile,hypothetical
/∗ The current speed example: STOP == 3; mph. ∗/
initially 5
Running final int a =initially3; // required
("Invalid final int STOP
private int currentAction
static the automobile, IDLE;
/∗ The
int currentSpeed MAX_SPEED= 5; 5
/∗ The current speed final int ∗/
private int react(TrafficSignal signal) by in which
action Third, the weak enumperforming, idle default
private
private int react(TrafficSignal signal) { IDLE; {
private
int to manually enumerate initially mph. ∗/
/∗ The reaction = this.react(aSignal); ∗/
if caseint currentSpeed = 5;return STOP;
TrafficSignal.RED:5;
(reaction != this.currentAction &&
private int currentSpeed = of{
ts, whichcase TrafficSignal.RED: return STOP;
privateincreases the likelihood
and Automobile.
case constants may beor go return STOP; these ne
TrafficSignal.RED:
//this.currentSpeed unin-
decide whether to stop <= MAX_SPEED)) ations
if
if TrafficSignal.RED: return STOP;
(this.shouldGo())
through compile-tim
case return INCREASE_SPEED;
else return STOP;
at compile timeTrafficSignal.GREEN: // noated values. It is als
case return STOP; into
inlined
// decide whether STOP; change
(a) return
return this.currentAction; change

this.currentAction && {
class case int color = RED;
Automobile
class Automobile {
INCREASE_SPEED ||
38 (reacti
private decide whether toDistinction: Enums vs. Constants
static final int IDLE = 0;
// Algorithmiccurrentor go ∗/
Accessor for the light’s stop color
for the light’s this.c
/∗ Accessor static { current color ∗/
class Automobile final int IDLE = 0;
private static
39
tSpeed <= MAX_SPEED)) final int INCREASE_SPEED = 1;
privateint getColor() {return this.color;}} this.
publicif static final int IDLE this.color;}}1;
(this.shouldGo())
public int getColor() int INCREASE_SPEED =
{return = 0;
rmAction(reaction);} final int DECREASE_SPEED = 2;
private static
private return INCREASE_SPEED; 41
private static { STOP; final int STOP = 3; 42 private
else return
Automobile {
class Automobile final int STOP = 3;
rmAction(int action) {...}} int DECREASE_SPEED = 2;
private static final
private static final int IDLE ==no change
static (b) Im
case static final int IDLE // 0;
3;
private enumerated types. currently performing, idle by default ∗/
MAX_SPEED = 140;
eger constantsaction this automobile isint INCREASE_SPEED ==1;
/∗ The for static final int INCREASE_SPEED
private static final is currently performing, idle by default ∗/
private this automobile MAX_SPEED = 140; 1;
/∗ The action
private static final int DECREASE_SPEED
default: currentAction = IDLE;
int throw new IllegalArgumentException
private int currentAction = IDLE; 2;
/∗ The action this automobile currently performing, idle by default ∗/
private
private static of the automobile,hypothetical
/∗ The current speed example: STOP == 3; mph. ∗/
initially 5
Running final int a =initially3; // required
("Invalid final int STOP
private int currentAction
static the automobile, IDLE;
/∗ The
int currentSpeed MAX_SPEED= 5; 5
/∗ The current speed final int ∗/
private int react(TrafficSignal signal) by in which
action Third, the weak enumperforming, idle default
private
private int react(TrafficSignal signal) { IDLE; {
private
int to manually enumerate initially mph. ∗/
/∗ The reaction = this.react(aSignal); ∗/
if caseint currentSpeed = 5;return STOP;
TrafficSignal.RED:5;
(reaction != this.currentAction &&
private int currentSpeed = of{
ts, whichcase TrafficSignal.RED: return STOP;
privateincreases the likelihood
and Automobile.
case constants may beor go return STOP; these ne
TrafficSignal.RED:
//this.currentSpeed unin-
decide whether to stop <= MAX_SPEED)) ations
if
if TrafficSignal.RED: return STOP;
(this.shouldGo())
through compile-tim
case return INCREASE_SPEED;
else return STOP;
at compile timeTrafficSignal.GREEN: // noated values. It is als
case return STOP; into
inlined
// decide whether STOP; change
(a) return
return this.currentAction; change

µ(P) {m | m "* % 1)!0#- "$ P}
υ(P) Top-level Enumerization Algorithm
{l | l "* % '%2"%,&) "$ P}
α '%2"%,&)/ !)&-/ 1)!0#-
αctxt 30"+$5+ "$ 40"+0 α 1%. #++(2
!"#$%& '( !)%*+,"-* .)/+/").(
.',/&4$'& Enumerize(F, P)
>A R ← Enumerizable(F )

QA R ← U nique(R) ∩ Distinct(R) ∩ Consistent(R)

GA 5,' *22 T ∈ R 4,

RA T ransf orm(T )
?A &#4 5,'

!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(

2)9%+!#2"$37 M) %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&.
45

µ(P) {m | m "* % 1)!0#- "$ P}
{l | l "* % '%2"%,&) "$ P}
α '%2"%,&)/ !)&-/ 1)!0#-
ic
αctxt 30"+$5+ "$ 40"+0 α 1%. #++(2 at
of st ds
et l ﬁel
bs a
!"#$%& '( !)%*+,"-* .)/+/").(
Su in
.',/&4$'& Enumerize(F, P) f


GA 5,' *22 T ∈ R 4,

RA T ransf orm(T )
?A &#4 5,'

!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(

2)9%+!#2"$37 M) %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&.
45

µ(P) {m | m "* % 1)!0#- "$ P}
{l | l "* % '%2"%,&) "$ P}
α '%2"%,&)/ !)&-/ 1)!0#-
αctxt 30"+$5+ "$ 40"+0 α 1%. #++(2
Orig
inal P
!"#$%&g '( !)%*+,"-* .)/+/").(
ro ra
.',/&4$'& Enumerize(F, m P)


GA 5,' *22 T ∈ R 4,

RA T ransf orm(T )
?A &#4 5,'

!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(

2)9%+!#2"$37 M) %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&.
45

µ(P) {m | m "* % 1)!0#- "$ P}
{l | l "* % '%2"%,&) "$ P}
α '%2"%,&)/ !)&-/ 1)!0#-
αctxt 30"+$5+ "$ 40"+0 α 1%. #++(2Infers which
!"#$%& '( !)%*+,"-* .)/+/").( being
candidate ﬁelds are
.',/&4$'& Enumerize(F, P) used as enums


GA 5,' *22 T ∈ R 4,

RA T ransf orm(T )
?A &#4 5,'

!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(

2)9%+!#2"$37 M) %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&.
45

µ(P) {m | m "* % 1)!0#- "$ P}
{l | l "* % '%2"%,&) "$ P}
α '%2"%,&)/ !)&-/ 1)!0#-
αctxt 30"+$5+ "$ 40"+0 α 1%. #++(2
!"#$%& '( !)%*+,"-* .)/+/").(


GA 5,' *22 T ∈ R 4,

RA T ransf orm(T ) Groups
?A &#4 5,'
them into minimal sets

!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(

2)9%+!#2"$37 M) %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&.
45

µ(P) {m | m "* % 1)!0#- "$ P}
{l | l "* % '%2"%,&) "$ P}
α '%2"%,&)/ !)&-/ 1)!0#-
αctxt 30"+$5+ "$ 40"+0 α 1%. #++(2
!"#$%& '( !)%*+,"-* .)/+/").(


GA 5,' *22 T ∈ R 4,

RA T ransf orm(T )
?A &#4 5,'

!"#$%& 0( 1)23,&4&, &.$*&%"5+/"). +,#)%"/6*(
Natural
ordering
2)9%+!#2"$37 M) %&*# %**(1) !0%! 4) %2) %,&) !# *!%!"+
"-)$!"9. %&& 2)9)2)$+)* !# +%$-"-%!) !)&-* %$- !2%$*"!"')&.
45

Empirical Evaluation
Benchmark KLOC Classes Sites Time (s)
ArtOfIllusion 75 378 111 207
Azureus 272 1894 635 1269
java5 180 1586 572 760
JavaCup 6 41 3 19
jdepend 3 28 1 1
JFlex 10 46 27 75
JFreeChart 71 420 43 128
jGap 6 137 5 7
jgraph 14 91 6 11
JHotDraw 29 496 24 14
junit 8 271 3 1
jwps 20 155 102 60
sablecc 29 237 10 9
tomcat6 153 1164 400 346
verbos 5 41 15 3
VietPad 11 84 22 8
Violet 7 73 20 9
Totals 899 7142 1999 2227
46

Azureus 272 1894 635 1269
java5 180 1586 572 760
JavaCup 6 41 3 19
jdepend 3 28 1 1
JFlex 10 46 27 75
jGap 6 137 5 7
jgraph 14 91 6 11
JHotDraw 29 496 24 14
junit 8 271 3 1
jwps 20 155 102 60
sablecc 29 237 10 9
tomcat6 153 1164 400 346
verbos 5 41 15 3
VietPad 11 84 2.4 / KLOC
22 8
Violet 7 73 20 9
Totals 899 7142 1999 2227
46

Azureus 272 1894 635 1269
java5 180
384 sites /
1586 572 760
JavaCup 6 Benchmark
41 3 19
jdepend 3 28 1 1
JFlex 10 46 27 75
jGap 6 137 5 7
jgraph 14 91 6 11
JHotDraw 29 496 24 14
junit 8 271 3 1
jwps 20 155 102 60
sablecc 29 237 10 9
tomcat6 153 1164 400 346
verbos 5 41 15 3
VietPad 11 84 22 8
Violet 7 73 20 9
Totals 899 7142 1999 2227
46

Filtered Contexts

47

Filtered Contexts

• Certain fields cannot be refactored.

47

Filtered Contexts

• Program semantics preservation depends on the
actual values of these fields.

47

Filtered Contexts

• For example, named-constants (used in
mathematical calculations).

47

Filtered Contexts

• Transitive dependency of an element outside
available source code.

47

Filtered Contexts

• Language constraints prohibit enumerization.
47

Filtered Contexts

• Remaining fields denoted as candidates.
47

Filtered Contexts

arr[RED]
• Remaining fields denoted as candidates.
47

Enum Identification Effectiveness

cands enum 48

0 140 280 420 560
ArtOfIllusion
Azureus
java5
JavaCup
jdepend
JFlex
JFreeChart
jGap
jgraph
JHotDraw
junit
jwps
sablecc
tomcat6
verbos
VietPad
Violet

cands enum 48

0 140 280 420 560
ArtOfIllusion
Azureus
java5
JavaCup
jdepend
JFlex
JFreeChart
jGap
jgraph Refactored
JHotDraw
junit 87%
jwps
sablecc
tomcat6
verbos
VietPad
Violet

cands enum 48

Result Summary

• 37% of all primitive constant fields identified as
candidates.

49

Result Summary

candidates.
• 87% of candidate fields found safe for refactoring.

49

Result Summary

candidates.
• Remaining 13% required more sophisticated analysis:

49

Result Summary

candidates.
• Explicit primitive conversion analysis (casts).

49

Result Summary

candidates.
• Explicit primitive conversion analysis (casts).
• Native array copying method usage.

49

Related Work

• Fowler [99] and Kerievsky [04] present a RE- PLACE
TYPE CODE WITH CLASS refactoring.

50

Related to a
Manual, not Work
language enum type,
and no inference


50

Related Work

• Deursen and Moonen [IWPC 99] identify
enumerated types in COBOL.

50

Related Work

Different
semantics
• preservation
Fowler [99] and Kerievsky [04] present a RE- PLACE
Tconstraints WITH CLASS refactoring.
YPE CODE


50

Related Work

• Gravley and Lakhotia [WCRE 96] identify
enumerated types in C.

50

Related Work

• Deursen and Moonen [IWPC 99] identify No
transitivity

50

Related Work

• Lawal and Lo [ASE 10] also identify enumerated
types in C, specifically, in Linux kernel.

50

Related Work

• Lawal and Lo [ASE 10] also identify enumerated
types in C, specifically, in Linux kernel.
Intra-
procedural
50

Conclusions

• Semantics preserving, declarative type inferencing
algorithm migrating legacy Java code to the enum
language construct introduced in Java 5.

51

Conclusions

• Implemented algorithm as a plug-in for the Eclipse
IDE and evaluated it on 17 open source applications:

51

Conclusions

• Analysis cost is practical.

51

Conclusions

• Weak enum pattern is commonly used in legacy
Java software.

51

Conclusions

• Weak enum pattern is commonly used in legacy
Java software.
• Proposal successfully refactors a large number of
static final fields into enumerated types.
51

Reasoning about Evolving AO Programs

52


• AOP enables modular implementation of CCCs.

52


• Both formal and informal reasoning about AOP
presents unique challenges especially in respect to
evolution.

52


• Both formal and informal reasoning about AOP
presents unique challenges especially in respect to
evolution.
• As components enter, exit, and re-enter software,
conclusions about behavior of components may be
invalidated.

52

A

C

Behavior of C+A
53

C

Behavior of C+A

53

The Invasiveness of AOP

54


• Desire a compositional reasoning approach, however
the invasive nature of AOP makes this difficult.

54


• Desire a compositional reasoning approach, however
the invasive nature of AOP makes this difficult.
• In the worst case, changes made to a single
component require reexamining the entire program.

54

Research Questions

55

Research Questions

• Can we draw meaningful conclusions about
component code without considering the actual
advice code?

55

Research Questions

advice code?
• Can we specify the behavior of components without
any particular advice in mind?

55

Research Questions

advice code?
• Can we parameterize specifications over all possibly
applicable aspects?

55

Research Questions

advice code?
• Can we parameterize specifications over all possibly
applicable aspects?
• Can we suitably constrain the behavior of aspects as
the software evolves?

55

Hiding Behind Interfaces

56


• Using interface is
one answer (e.g.,
XPIs [Griswold
’06], Open Modules
[Aldrich ’05])

56


• Using interface is
one answer (e.g.,
XPIs [Griswold
’06], Open Modules
[Aldrich ’05])

• But it would be nice
to have a way to
derive the enriched
behavior of the base
plus the aspects at
compile time. 56

Contributions

• Developed an approach to specify the behavior of
aspects so that:

57

Contributions

aspects so that:
• They can be combined with the behavior of the base-
code to arrive at the overall system behavior

57

Contributions

aspects so that:
• Are not invalidated upon evolution.

57

Contributions

aspects so that:
• Are not invalidated upon evolution.
• Inspired subsequent work by Bagherzadeh et al.
[AOSD 11].

57

Proposal

• AO programs inherently enjoy plug-n-play
capabilities [Laddad ’03]

58

Proposal

• Crosscutting features can be plugged-in to enrich the
behavior of advised components.

58

Proposal

• Crosscutting features can be plugged-in to enrich the
behavior of advised components.
• My proposal involves developing an reasoning
technique that enables developers to specify
components so that their behaviors can be derive in a
similar fashion.

58

Spec(C)

Spec(A1 ) Spec(A2 )

A1 C A2

Spec(A1 ) Spec(C) Spec(A2 )


Compose

Behavior of C+A1


Compose

Compose
Behavior of C+A1 Behavior of C+A2


Compose

Compose

Compose
Behavior of C+A1 Behavior of C+A1+A2 Behavior of C+A2

Obstacles

• Usefulness

60

Obstacles

• Usefulness
• Is it possible to draw meaningful conclusions from
such incomplete information?

60

Obstacles

• Usefulness
• Obliviousness

60

Obstacles

• Usefulness
• Obliviousness
• Specifications contain “slots” for applications of
crosscutting concerns.

60

Obstacles

• Abstraction

61

Obstacles

• Abstraction
• Competing forces:

61

Obstacles

• Abstraction
• Specs abstract internal details components,
aspects directly manipulate them.

61

Obstacles

• Abstraction
• Composition

61

Obstacles

• Abstraction
• Composition
• Which pegs go into which holes?

61

Obstacles

• Abstraction
• Composition
• How to deal with dynamic and lexical pointcuts?

61

Obstacles

• Abstraction
• Composition
• Complexity
61

Obstacles

• Abstraction
• Composition
• Complexity
• What if no advice is applicable?
61

Tackling Specification Complexity

62


• May need to make assumptions about the behavior of
evolving components.

62


• Specification pointcuts

62


• Pointcut interfaces [Gudmundson ’01] annotated
with behavioral specifications.

62


• “Exported” internal semantic events within the
component.

62


component.
• Adopt a rely-guarantee approach [Xu ’97] from
concurrent programming to constrain the behavior
of all possibly applicable advice using a rely clause.

62


component.
• Adopt a rely-guarantee approach [Xu ’97] from
concurrent programming to constrain the behavior
of all possibly applicable advice using a rely clause.
• A guar clause may be used to constrain components. 62

Review of R/G for AOP [Khatchadourian07,
Soundarajan07]

the set of all variables of
σ the program

states in which each
σi , σj , ... variable has a particular
value

63

Techniques for Automated Software Evolution

The state at a point in the execution
of a component is σa.

!a

Aspect

!b

66


!a

Aspect

!b

The state when the class gets control
back from an aspect is σb.
66


!a

Aspect
rely(σa, σb)

!b

The state when the class gets control
back from an aspect is σb.
66

Rely() Example

rely(σ, σ ) ≡ (σ = σ )

67

Rely() Example

The entire state of
C

rely(σ, σ ) ≡ (σ = σ )

67

Rely() Example

rely(σ, σ ) ≡ (σ = σ )

le y
ab an
lic g
pp kin e!
a a
ny m stat
s a om he
id fr
rb e t
o ic
F v in
d ang es
a
ch 67

Rely() Example

This is
“Harmless”[DW
POPL’06]

rely(σ, σ ) ≡ (σ = σ )

67

Deriving Effective Behavior

68


• Constraining parameterized behavior reduces
complexity, but ...

68


complexity, but ...
• How are formal parameters expressed?

68


complexity, but ...
• How are actual parameters deduced?

68


complexity, but ...
• How are the specifications composed?

68


complexity, but ...
• Aspects are typically used to enrich the behavior of
the an underlying component.

68


complexity, but ...
• Aspects are typically used to enrich the behavior of
the an underlying component.
• Thus, desire to derive the actual behavior of
components combined with the aspects.
68

Join Point Traces

69

Join Point Traces

• A Join Point Trace (JPT) variable is introduced to
track the flow-of-control through various join points
within a component.

69

Join Point Traces

within a component.
• A JPT is used as a parameter over the actions of all
possibly applicable aspects.

69

Join Point Traces

within a component.
• Method post-conditions will references to the JPT.

69

Join Point Traces

within a component.
• Method post-conditions will references to the JPT.
• Informally, a JPT is used to refer to the actions and
resulting values taken by advice at certain join point.

69

Elements of the JPT

70

Elements of the JPT

• The JPT is composed of several components that are
associated with each join point.

70

Elements of the JPT

• The JPT is composed of several components that are
associated with each join point.
• Just as there are different kinds of join points (e.g.,
call, execution), there different kinds of JPT
entries.

70

JPT Method Call Completion Element

(oid , mid , aid , args, res, σ, σ )

71



Called Object

71


Called
Method


Called Object

71


Called
Method


Applicable
Called Object
Aspect

71


Called Argument
Method Values


Applicable
Called Object
Aspect

71


Called Argument
Method Values


Applicable Method
Called Object Return Value
Aspect

71


σ, σ

71


State Vectors

σ, σ

71


State Vectors

σ, σ
σ[oid] State of object oid after
completion of method mid

71


State Vectors

σ, σ
σ [oid]
State of object oid after
completion of aspect aid

71


State Vectors

σ, σ
σ [oid]
State of object oid after
completion of aspect aid
No applicable advice =⇒ σ = σ

71

Rule for method specification

72


Normal
pre-condition

72


Post-condition, may
include references to
portions of JPT
72


R/G Clauses

72


73


Invocation of C.m
on the local JPT

73


74


Classic
Hoare Triple

74


75


Don’t forget
about the
guarantee

75


76


If when q holds and
applicable advice behaves
properly implies that ...

76


77


... our post-
condition holds with a a
new entry in the local
JPT

77


Not sure which
aspect is applicable yet, so
we’ll leave this blank

77


Replace all
occurrences of
σ with σ’

77

Rule for Method Calls

78


79


Substitute
actuals for formals

79


80


Local JPT for
caller

80


Local JPT for
callee

80


Substitute
formals for actuals

80

Rule for Aspect Application (Simple)

81


Base-code
plus an aspect

81


Base-code
pre-condition

81


Aspect pre-
condition

81


Base-code
post-condition

81


Aspect post-
condition

81


82


Base-code
satisﬁes guar

82


Advice body

82


State
vector immediately
prior to the execution
of the advice

82


83

Future Work

• (More) Complete axiomatic proof system.

84

Future Work

• Develop for a core calculus, expand as necessarily.

84

Future Work

• Advice advising other advice.

84

Future Work

• Multiple advice acting on a single join point.

84

Future Work

• Dealing with object aliasing.

84

Future Work

• Dealing with object aliasing.
• Separation Logic [Ishtiaq, O’Hearn ’01] may help.
84

Future Work

• Curbing complexity:

85

Future Work

• Specifications may (easily!) become unwieldy.

85

Future Work

• Find suitable restrictions on aspects.

85

Future Work

• Module “sealing” ([Aldrich ’05])

85

Future Work

• Advice not applicable to internal join points.

85

Future Work

• Semi-automation:

85

Future Work

• Integration with IDE/theorem provers, AJDT.
85

Future Work

• Integration with IDE/theorem provers, AJDT.
• Extend specification languages (e.g., JML, Pipa)
85

Conclusion

• Presented techniques to:

86

Conclusion


86

Conclusion

3.Robustly specify evolving Aspect-Oriented software
components.

86

Techniques for Automated Software Evolution

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