Question

I have class A and B which inherit from Base.

Base has a private method. It is possible that A and B execute this method at the same time.

So I want to synchronize that method. If I just put “synchronize” keyword in the signature, will that make that A and B execution is synchronized (share the same lock) ? Or do I need to generate a static lock object…?

Sorry, a bit confused…

Answer 1

If your code looks a bit like the example below, then it is not thread safe and you need to include some form of synchronization to make sure the call to the private method increment is atomic and ensure visibility. In that simple example, making getNewCounter synchronized would be enough. Using a lock object would work too.

public class Base {
    private int counter;

    private void increment() {
        counter++;
    }
    protected int getNewCounter() {
        increment();
        return counter;
    }
}

public class A extends Base {
    public int aMethod() {
        return getNewCounter();
    }
}

public class B extends Base {
    public int anotherMethod() {
        return getNewCounter();
    }
}