Can two threads run two different methods at the same point of time?

Question

class A {
    private synchronized f() {
        ...
        ...
    }

    private void g() {
        ...
        ...
    }
}

If thread T1 is running f() which is synchronized, can thread t2 run g() which is not synchronized at the same point of time, while T1 is still running f()?

Answer 1

Not on the same instance of A. The instance itself is the lock so two execute the two methods at the same time with two threads you would need two instances of A.

Answer 2

Yes. Both methods can execute at the same time on the same instance.

Only f() is synchronized. A thread must acquire the monitor for this.f() to execute f() and only one monitor exists per instance.

g() is not synchronized, no monitor locking is required to run the method, so any thread can execute g() at any time.

"A synchronized method acquires a monitor (§17.1) before it executes."

http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.4.3.6