What is the use of synchronized block inside constructor?

Question

We can not make constructor synchronized but can write synchronized this inside constructor. In what case such requirement will come ? I am amused.

package com.simple;
public class Test {
    public Test() {
        synchronized (this) {
            System.out.println("I am called ...");
        }
    }

    public static void main(String[] args) {
        Test test=new Test();   
        System.out.println(""+test);
    }

    @Override
    public String toString() {
        return "Test []";
    }
}

Answer 1

Well, you could start a new thread within the constructor. It would be highly unusual - and certainly in the code you've provided it would be pointless - but it could happen.

Languages don't typically try to find every possibly thing you could do that would be pointless - it would lead to a very complex language specification. There has to be some degree of thought on the part of the language users, too...

Answer 2

Synchronizing on this would be a sign of bad practice because it would imply you are leaking this out of the constructor: this is the only way you could have some other code synchronizing on the same object.

Synchronizing on some other common lock, however, could be legitimate: the constructor my indeed involve calling some code that requires such synchronization.