Inter thread communication & runnable interface

Inter-thread communication
&
Runnable Interface

Inter-thread communication
• Cooperation (Inter-thread communication) is a
mechanism in which a thread is paused
running in its critical section and another
thread is allowed to enter (or lock) in the
same critical section to be executed. It is
implemented by following methods of Object
class: wait() notify() notifyAll()

Methods:-
• wait()
• notify()
• notifyAll()

wait() method
• Causes current thread to release the lock and
wait until either another thread invokes the
notify() method or the notifyAll() method for
this object, or a specified amount of time has
elapsed.

notify() method
• Wakes up a single thread that is waiting on
this object's monitor. If any threads are
waiting on this object, one of them is chosen
to be awakened. The choice is arbitrary and
occurs at the discretion of the
implementation.
Syntax:
public final void notify()

notifyAll() method
• Wakes up all threads that are waiting on this
object's monitor.
Syntax:
public final void notifyAll()

Process of inter-thread
communication

Explantion of above Diagram:-
• Threads enter to acquire lock.
• Lock is acquired by on thread.
• Now thread goes to waiting state if you call wait()
method on the object. Otherwise it releases the lock
and exits.
• If you call notify() or notifyAll() method, thread moves
to the notified state (runnable state).
• Now thread is available to acquire lock.
• After completion of the task, thread releases the lock
and exits the monitor state of the object.

Runnable interface
• The Runnable interface should be implemented by
any class whose instances are intended to be
executed by a thread.
• The class must define a method of no arguments
called run .
• This interface is designed to provide a common
protocol for objects that wish to execute code while
they are active.

Create a Thread by Implementing a
Runnable Interface
• If your class is intended to be executed as a
thread then you can achieve this by
implementing a Runnable interface.
• You will need to follow three basic steps.

Step 1
• As a first step, you need to implement a run()
method provided by a Runnable interface.
This method provides an entry point for the
thread and you will put your complete
business logic inside this method.
• Following is a simple syntax of the run()
method
• public void run( )

Step 2
• As a second step, you will instantiate
a Thread object using the following
constructor
• Thread(Runnable threadObj, String threadName);
• Where, threadObj is an instance of a class that
implements the Runnable interface
and threadName is the name given to the
new thread.

Step 3
• Once a Thread object is created, you can start it by
calling start() method, which executes a call to run( )
method. Following is a simple syntax of start() method.
• void start();
• Example:
 Write a JAVA program which will create two child
threads by implementing Runnable interface; one
thread will print even nos from 1 to 50 and other
display vowels from accepted string.

import java.io.*;
import java.util.*;
class Even implements Runnable
{
public void run()
{
for(int i=1;i<=50;i++)
{
if(i%2==0)
System.out.println("Even no " +i);
}
}
}
class Vowel implements Runnable
{
public void run()
{
try
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter the string");
String data=br.readLine();
int len=data.length();
for(int i=0;i<len;i++)
{
if(data.charAt(i)=='a'|| data.charAt(i)=='e'|| data.charAt(i)=='i'|| data.charAt(i)=='o'|| data.charAt(i)=='u' ||
data.charAt(i)=='A'|| data.charAt(i)=='E'|| data.charAt(i)=='I'|| data.charAt(i)=='O'|| data.charAt(i)=='U')
System.out.println("Vowel in entered string at position "+(i+1)+" is "+data.charAt(i)); } }
catch(Exception e){} }
}

class EvenVowel
{
public static void main(String args[])
{
try
{
Even no=new Even();
Thread t1=new Thread(no);
t1.start();
t1.sleep(1000);
Vowel ch=new Vowel();
Thread t2=new Thread(ch);
t2.start();
}
catch(Exception e){}
}
}

Inter thread communication & runnable interface

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