forum

Home / DeveloperSection / Forums / Synchronized thread method in java

Ask Question

Synchronized thread method in java

Elena Glibart250129-Oct-2014
I have one question about thread. I have following Thread class and creating 2 thread objects.

publicclassMyThread extends Thread{
 
    String name="";
 
    public MyThread(String string) {
        name=string;
    }    
 
    @Override
    publicvoid run() {
        callMe();
    }        
    synchronized privatevoid callMe() {
        System.out.println("Started");
        for (int i = 1; i <= 5; i++) {
            System.out.println(name+" = "+i);
        }           
    }
 
 
    publicstaticvoid main(String[] args) {                    MyThread a = newMyThread("A");
        MyThread b = newMyThread("B");
 
        a.start();
        b.start();
    }       }

Output:

Started

Started

B = 1

B = 2

A = 1

A = 2

B = 3

A = 3

B = 4

A = 4

B = 5

A = 5

my question is: why loop is NOT executed one after other? I have used synchronized keyword.

javajava thread multiple threading 
Updated on 29-Oct-2014
Elena Glibart

Elena Glibart

Follow

Can you answer this question?

Answer

1 Answers

marcel ethan

marcel ethan

29-Oct-2014
Your synchronized method is effectively:
privatevoid callMe() {
    synchronized(this) {
        System.out.println("Started");
        for (int i = 1; i <= 5; i++) {
            System.out.println(name+" = "+i);
        }
    }
}

Now you've created two different instances, so this will be different for each thread... so they're not synchronizing against each other. If you want to see two threads working with the same monitor, you could rewrite your code like this:

public final classDemoRunnable implements Runnable {
    @Override
    public synchronized void run() {
        System.out.println("Started");
        for (int i = 1; i <= 5; i++) {
            System.out.println(Thread.currentThread().getName() + " = " + i);
        }
    }
 
    publicstaticvoid main(String[] args) {
        Runnable runnable = newDemoRunnable();
        Thread a = newThread(runnable, "A");
        Thread b = newThread(runnable, "B");
        a.start();
        b.start();
    }
}

Output:

Started

A = 1

A = 2

A = 3

A = 4

A = 5

Started

B = 1

B = 2

B = 3

B = 4

B = 5

Liked By