Question

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();  //tricky assignement
          c=b;                      //one object eligible GC
          c.aob=null;
          System.gc();
     }
}

There is two objectcs eligible for garbage collection but one is difficult to understand.

A d=new A().aob=new A();

1) This line I thing that it would make this

A d = new A().aob = new A();
          ^             ^
          O1            O2

      O1 --> O2 --> null
      ^
      |
d ----| 

2) But what really is doing is this (so one eligible object) WHY IS LIKE THIS?

A d = new A().aob = new A();
          ^             ^
          O1            O2

      O1 --> O2 --> null
             ^
             |
d -----------| 

because the assignements are associative right to left.

A d = ( new A().aob = new A() );

Could anyone explain it otherwise?
Thanks

Answer 1

It starts from right to left. First new A() is executed and a new object is created. Then it is assigned to the field aob of another new object A. Finally d is referencing the property aob. This means the second object A is eligible for garbage collection.

It is like:

A firstA = new A();
A secondA = new A();
secondA.aob = firstA;
A d = secondA.aob;

But the secondA object is created inline so there are no references to it and it is eligible for garbage collection.