How many object are eligible for gc - problem

[Mark Moge]

This is excercise from "ExamLab for SCJP 6.0"
How many objects are eligible for the gc after executing statement "c.aob=null"

  
class A{
   A aob;
   public static void main (String[] args){
      A a = new A();
      A b = new A();
      A c = new A();
      a.aob = b;
      b.aob = a;
      c.aob = a.aob;
      A d = new A().aob =new A(); // d points to new object and aob of new object points to another new object (is it correct?)
      c = b;
      c.aob = null;
      System.gc();
   }
}  

I made a graph and I can see only one object eligible for gc. The answer is 2. So can you show me where is my mistake?

[Siva Masilamani]

Even i see only one object eligible for GC which was referred by c initially.

[Ankit Garg]

A d = new A().aob =new A();
This is the key line here. There is one object eligible for GC here. The object in bold is actually assigned to d and the object in italics is eligible for GC...

[Ireneusz Kordal]

Here:

  
A d = new A().aob =new A(); // d points to new object and aob of new object points to another new object (is it correct?)    

d points to the last object created with new A(), not the object created with new A().aob.
Object new A.aob is eligible to gc since there is no reference that points to it.
And the total number of objects eligible for gs is 2.

Look at this example.

public class Test {
    private final String name;
    public Test t;
    Test(String s){
        name = s;
    }
    String getName(){
        return name;
    }

    public static void main(String ... a){
        Test t = new Test("A").t = new Test("B"); // <------------------
        System.out.println("Object = " + t.getName()); // result: Object = B, not A
    }
}

[Mark Moge]

Thanks for clarifying. Now I can see how it works.

[Prithvi Sehgal]

I can smell in air, that why ExamLab is considered to be tough.

I must praise Devaka for putting such a great effort and making it open-source for the community.
My special thanks to Devaka.

Best Regards,

[Devaka Cooray]

Prithvi Sehgal wrote:... and making it open-source for the community.

Open-Source ???

[Prithvi Sehgal]

Apologies Devaka wrong word i must say. Not open-source.
To my knowledge, before somtime, ExamLab was free , i am not really sure if you have updated it at commercial level.
Let me know.

Best Regards,

[Devaka Cooray]

Prithvi Sehgal wrote:i am not really sure if you have updated it at commercial level.

Nope, and never