GC (Dan Question)

[munna next]

    
class A {
  private String name;
  private A otherA;
  public A(String name) {this.name = name;}
  public void other(A otherA) {this.otherA = otherA;}
  public A other() {return otherA;}
  public String toString() {return name;}
  protected void finalize() {System.out.print(name);}
}
class B {
  public static void m1() {
    A a1 = new A("A1"), a2 = new A("A2"), a3 = new A("A3"), a0 = a3;
    a1.other(a2); a2.other(a3); a3.other(a1);
    for(int i = 0; i<4; i++){System.out.print(a0 = a0.other());}
  }
  public static void main(String[] args) {m1(); System.gc();}
}
 
Which of the following could be a result of attempting to compile and run the program? 
 
a.  A1A2A3A1 
b.  A0A0A0A0A1A2A3 
c.  A1A2A3A1A2A3 
d.  A1A2A3A1A1A2A3 
e.  A1A2A3A1A3A2A1 
f.  A0A1A2A3A1A2A3 
 
Answer: a  c  d  e  

Explonations is



The three instances of class A form an isolated ring where each instance references the next instance and the third references the first instance. Four iterations of the for loop are processed. Inside the body of the for statement, the invocation of the print method contains the argument expression a0 = a0.other(). On the first iteration, the reference variable a0 references the instance named A3. The value returned by the method named other is a reference to the instance named A1. The reference is assigned to the reference variable a0 and is also the value produced by the expression a0 = a0.other(). That reference value is passed as an argument to the print method, and the print method invokes the A.toString method. With each iteration of the loop, the reference moves to the next object in the loop and the name of the object is printed. After four iterations, the loop ends and the method m1 returns. The invocation of the System.gc method serves as a suggestion that the garbage collector should be allowed to run. The system could ignore the suggestion, so there is no guarantee that the eligible arguments will be garbage collected. If they are collected, there is no guarantee which will be collected first. The only guarantee is that the finalize method will be invoked on each particular instance before the resources that had been allocated to that instance are reclaimed.

I have not understand the point

I have not understand the below wording

"(). On the first iteration, the reference variable a0 references the instance named A3. The value returned by the method named other is a reference to the instance named A1"


I know it is very difficult to explain with out face-to-face. But If anybody try to explain I will be thankfull.

[ July 25, 2006: Message edited by: munna next ]
[ July 25, 2006: Message edited by: munna next ]

[Barry Gaunt]

The best way to tackle these problems is draw a diagram. Work through the execution drawing a balloon for each object that is created. Show how the objects are connected together by drawing strings between them. You will end up with a connected structure of balloons without a reference to them from the main thread of execution. When the garbage collector runs some or all of those balloons will run their finalizers printing out their contents in some order.
[ July 25, 2006: Message edited by: Barry Gaunt ]