Java Class Design
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This document discusses various topics related to Java class design including: - The first object oriented programming language was Simula from 1965 - Examples are provided to demonstrate polymorphism and abstract classes in Java - The java.time package provides improved date/time functionality over java.util.Date - Design principles like single responsibility, open/closed, Liskov substitution, and others are covered - Tools for exploring class design structures like dependencies are listed - Local meetups focused on software design and development are shared.
![Guess the output
class Base {
public Base() {
foo();
}
public void foo() {
System.out.println("In Base's foo ");
}
}
class Derived extends Base {
public Derived() {
i = new Integer(10);
}
public void foo() {
System.out.println("In Derived's foo " + i.toString() );
}
private Integer i;
}
class Test {
public static void main(String [] s) {
new Derived();
}
}](https://image.slidesharecdn.com/javaclassdesign-160921044318/85/Java-Class-Design-7-320.jpg)
![Guess the output
abstract class Printer {
private Integer portNumber = getPortNumber();
abstract Integer getPortNumber();
public static void main(String[]s) {
Printer p = new LPDPrinter();
System.out.println(p.portNumber);
}
}
class LPDPrinter extends Printer {
/* Line Printer Deamon port no is 515 */
private Integer defaultPortNumber = 515;
Integer getPortNumber() {
return defaultPortNumber;
}
}](https://image.slidesharecdn.com/javaclassdesign-160921044318/85/Java-Class-Design-8-320.jpg)
![Revisiting the example …
You can use only date,
time, or even timezone,
and combine them as
needed!
LocalDate today = LocalDate.now();
System.out.println(today);
LocalTime now = LocalTime.now();
System.out.println(now);
ZoneId id = ZoneId.of("Asia/Tokyo");
System.out.println(id);
LocalDateTime todayAndNow = LocalDateTime.now();
System.out.println(todayAndNow);
ZonedDateTime todayAndNowInTokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));
System.out.println(todayAndNowInTokyo);
2016-03-17
13:28:06.927
Asia/Tokyo
2016-03-17T13:28:06.928
2016-03-17T16:58:06.929+09:00[Asia/Tokyo]](https://image.slidesharecdn.com/javaclassdesign-160921044318/85/Java-Class-Design-15-320.jpg)
Java Class Design
- 1. Java Class Design Ganesh Samarthyam ganesh@codeops.tech
- 2. Name the first object oriented programming language
- 6. OOP sometimes becomes ❖ Uh-oh or ❖ Oops!
- 7. Guess the output class Base { public Base() { foo(); } public void foo() { System.out.println("In Base's foo "); } } class Derived extends Base { public Derived() { i = new Integer(10); } public void foo() { System.out.println("In Derived's foo " + i.toString() ); } private Integer i; } class Test { public static void main(String [] s) { new Derived(); } }
- 8. Guess the output abstract class Printer { private Integer portNumber = getPortNumber(); abstract Integer getPortNumber(); public static void main(String[]s) { Printer p = new LPDPrinter(); System.out.println(p.portNumber); } } class LPDPrinter extends Printer { /* Line Printer Deamon port no is 515 */ private Integer defaultPortNumber = 515; Integer getPortNumber() { return defaultPortNumber; } }
- 9. Date & time exercise ❖ Your project requires support for date and time functionality ❖ Assume that the Java library or third-party library support is not available for date and time related functionality ❖ Will you provide separate classes for date, time and timezone or a single class that supports all the three? How to support calculating differences between two date/time values?
- 10. Class design problem: Example
- 11. Discussion example // using java.util.Date Date today = new Date(); System.out.println(today); $ java DateUse Wed Dec 02 17:17:08 IST 2015 Why should we get the time and timezone details if I only want a date? Can I get rid of these parts? No!
- 12. So what! Date today = new Date(); System.out.println(today); Date todayAgain = new Date(); System.out.println(todayAgain); System.out.println(today.compareTo(todayAgain) == 0); Thu Mar 17 13:21:55 IST 2016 Thu Mar 17 13:21:55 IST 2016 false What is going on here?
- 14. Solution LocalDate today = LocalDate.now(); System.out.println(today); LocalDate todayAgain = LocalDate.now(); System.out.println(todayAgain); System.out.println(today.compareTo(todayAgain) == 0); 2016-03-17 2016-03-17 true Works fine now!
- 15. Revisiting the example … You can use only date, time, or even timezone, and combine them as needed! LocalDate today = LocalDate.now(); System.out.println(today); LocalTime now = LocalTime.now(); System.out.println(now); ZoneId id = ZoneId.of("Asia/Tokyo"); System.out.println(id); LocalDateTime todayAndNow = LocalDateTime.now(); System.out.println(todayAndNow); ZonedDateTime todayAndNowInTokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo")); System.out.println(todayAndNowInTokyo); 2016-03-17 13:28:06.927 Asia/Tokyo 2016-03-17T13:28:06.928 2016-03-17T16:58:06.929+09:00[Asia/Tokyo]
- 16. More classes in Date/Time API
- 18. Interface hierarchy for polymorphism
- 20. Assign responsibilities correctly class GraphicsDevice public void setFullScreenWindow(Window w) { if (w != null) { if (w.getShape() != null) { w.setShape(null); } if (w.getOpacity() < 1.0f) { w.setOpacity(1.0f); } if (!w.isOpaque()) { Color bgColor = w.getBackground(); bgColor = new Color(bgColor.getRed(), bgColor.getGreen(), bgColor.getBlue(), 255); w.setBackground(bgColor); } } … }
- 21. Keep data members private
- 22. Protect from direct external mutations
- 23. Ensure each class has a single responsibility
- 24. Adhere to IS-A relationship
- 26. SOLID Principles S Single Responsibility Principle Every object should have a single responsibility and that should be encapsulated by the class O Open Closed Principle Software should be open for extension, but closed for modification L Liskov’s Substitution Principle Any subclass should always be usable instead of its parent class I Interface Segregation Principle Many client specific interfaces are better than one general purpose interface D Dependency Inversion Principle Abstractions should not depend upon details. Details should depend upon abstractions
- 27. Tools to explore Jhawk (Java) CodeCity (C++, Java, C#) CppDepend (C++) Sotograph (C++, Java, C#) Imagix 4D (C, C++, Java) Lattix (C/C++, Java, C#) SolidSX (C++, Java, C#) Bauhaus (C/C++, Java, C#) Structure101 (Java, C#) Understand (C/C++, Java, C#) Simian (C/C++, Java, C#, …) Jarchitect (Java) Ndepend (C#) Stan4J (Java) InFusion (C/C++, Java) InCode (C/C++, Java)
- 29. ganesh@codeops.tech @GSamarthyam www.codeops.tech slideshare.net/sgganesh +91 98801 64463 bit.ly/ganeshsg