Garbage collection problem

[Mark Guo]

public class TestGC {
	TestGC t;
	public static void main(String[] args) {
		TestGC t = new TestGC();
		TestGC t2 = t.go(t);
                t2 = null;
	}
	
	TestGC go(TestGC t) {
		TestGC t1 = new TestGC();
		TestGC t2 = new TestGC();
		t1.t = t2;
		t2.t = t1;
		t.t = t2;
		return t1;
	}
}

when line 7 is reached, how many objects are eligible for garbage collection?

[Mohamed Sanaulla]

I think its None. Cause each of the instances are accessible via some reference.

[Ankit Garg]

If this is a mock exam question, then please QuoteYourSources...

[Stephan van Hulst]

Actually, it's 3.

The go method will create two new objects, which will refer to each other. Then, it will let the argument refer to the one, and the method will return the other.

The main method creates a new object, which is passed to the go method. So this object will now refer to one of the two new objects in the go method, and t2 will now refer to the other object returned from the method.

Then, the method goes out of scope, so all objects become eligible for collection (note that t hides the instance member t).

If the question means that by line 7 the method hasn't gone out of scope yet, then no object is eligible, since t still has a reference to one of them, which has a reference to t2 in go, which has a reference to t1 in go.

[Mohamed Sanaulla]

And I considered that the method has not gone out of scope Thanks Stephan for the explanation.

[Adolfo Eloy]

Stephan van Hulst wrote:
Then, the method goes out of scope, so all objects become eligible for collection (note that t hides the instance member t).

Stephan, when you say that the method goes out of scope are you considering the "main" method or "go" method?
Because I think that if you are talking about the go method, no objects will be collected but if you are considering the main method going out of scope so I agree.

I'm only asking to understand better this question.

Thanks.

[Stephan van Hulst]

I meant the main method.