confusion about object lock.

[pawan chopra]

Hi All,

I have a class as shown below:

public class ThreadSafeImpl {
    
    
    public synchronized void firstMethod(){
        System.out.println("Executing first method!");
    }
    
    public synchronized void secondMethod(){
        System.out.println("Executing second method!");
    }

}

this class has two methods they are synchronized. Now let us say thread 1 is executing firstMethod while its executing that thread 2 tries to execute the second method on same object. Will it be able to execute it or not? If yes then how come this is lock on a object? I hopw this is not a silly question. Please help.

[Christophe Verré]

When a synchronized method of an object is called, all other synchronized of the same object will block until the executed method ends.

[Christophe Verré]

Here is an example where the first method sleeps 5 seconds. Check what happens with and without the synchronized keyword on the second method.

class ThreadSafe {
    public synchronized void firstMethod(){
        System.out.println("Executing first method!");
        try {
			Thread.sleep(5000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
    }
    
    public synchronized void secondMethod(){
        System.out.println("Executing second method!");
    }
}

public class ThreadSafeImpl {
	public static void main(String[] args) {
		final ThreadSafe ts = new ThreadSafe();
		new Thread(new Runnable() {
			public void run() {
				ts.firstMethod();
			};
		}).start();
		new Thread(new Runnable() {
			public void run() {
				ts.secondMethod();
			};
		}).start();
	}
}

[pawan chopra]

Thanks a lot Christophe!