该对象什么时候可以进行垃圾收集？

Question

I have this piece of code, and I am confused about when the Object o becomes eligible for garbage collection in Java.

    public class JustSo
    {
        public static void main(String[] args)
        {
             for(int i=0;i<4;i++)
             {
                     Object o=new Object();
                     //o.doSomething();
             }
             System.out.println("DONE");
        }
    }

Since it is inside a loop(or any block for that matter), it will become eligible at the end of the loop right?

But I found an answer on a reliable developer site(Don't want to disclose where) that says the earliest the object becomes eligible is at the print statement.

Please clarify.

Answer 1

When it becomes out of scope, so after each iteration of the for loop. An object is eligible for garbage collection when it is no longer reachable, this occurs in 2 situations.

• The object no longer has any references point to it.
• All references to the object have gone out of scope.

The latter is the situation for the object in question, and it the object's reference is out of scope after the for loop. Prior to the print statement.

Answer 2

Since you are not saving the reference into some outer-scope variable,and creating new instance each time as soon as single iteration complete, its eligible for garbage collection.

So when you came out of loop, all the objects created inside eligible for GC.

May be you confused with author wording here. Consider below code

 for(int i=0;i<4;i++)
             {
                     Object o=new Object();
                     //o.doSomething();
             } -----> objects ready for GC here. 
             // some other code  
             // some other code
             System.out.println("DONE");

Answer 3

As the oracle documentation about the garbagecollector says:

Automatic garbage collection is the process of looking at heap memory, identifying which objects are in use and which are not, and deleting the unused objects. An in use object, or a referenced object, means that some part of your program still maintains a pointer to that object. An unused object, or unreferenced object, is no longer referenced by any part of your program. So the memory used by an unreferenced object can be reclaimed.

This means as soon as an Object isn't referenced from any other Object or is out of scope, it will be marked for deletion. In this case, the reference is out of scope, each time the loop starts again (just before every increment). Thus each object will be marked for deletion at the end of the loop (before the next loop-repetition).

Answer 4

每次循环时，大约在i++发生时，该对象将符合GC的条件。