Question

Consider the following piece of code –

class MyThread extends Thread {
    private int x = 5;

    public void run() {
        synchronized (this) // <-- what does it mean?
        {
            for (int i = 0; i < x; i++) {
                System.out.println(i);
            }
            notify();
        }
    }
}

class Test {
    public static void main(String[] args) {
        MyThread m = new MyThread();
        m.start();

        synchronized (m) {
            try {
                m.wait();
            } catch (InterruptedException e) {

            }
        }
    }
}

In the above example, does Thread m acquire the lock on itself?

Answer 1

The current thread acquires the lock on the associated instance of the MyThread class.

The synchronized(this) is locking the same object as synchronized(m) in main().

Finally,

public void run() {
    synchronized (this) {

is exactly equivalent to

public synchronized void run() {