调用new Object（）; 两次使第一次调用创建的对象有资格进行垃圾回收？

Question

Given:

    1. public class GC {
    2.    private Object o;
    3.    private void doSomethingElse(Object obj) { o = obj; }
    4.    public void doSomething() {
    5.       Object o = new Object();
    6.       doSomethingElse(o);
    7.       o = new Object();
    8.       doSomethingElse(null);
    9.       o = null;
    10.   }
    11. }

When the doSomething() method is called, after which line does the Object created in line 5 becomes available for garbage collection?

The correct answer is Line 8.

Why is that? I think it should be Line 7 because new will initiate a new Object and then assigned to o , which resulted in the Object created in Line 5 lose its reference (then become eligible for GC). Am I wrong?

Answer 1

The correct answer is Line 8. Why is that?

You are confusing the o local to doSomething() with the o that is at the class level. Even though line 7 sets the doSomething() version of o to some other reference, you still have the class-level o that was set through the doSomethingElse() method. You have to null that reference to make it GC eligible, and that only happens by the method call on line 8.