another GC question help

[wei liu]

hi guys the quest below is on SCJP book Page 284 question 11;

 
 class Beta {}
 clas Alpha {
    static Beta b1;
    Beta b2;
  }

   public class Tester{
     public static void main(String[] args){

       Beta b1=new Beta();
       Beta b2=new Beta();
       Alpha a1=new Alpha();
       Alpha a2=new Alpha();
       a1.b1=b1;
       a1.b2=b1;
       a2.b2=b2;

       a1=null;
       b1=null;
      b2=null; 
    //do stuff

}
}

   

the question is until the code to do stuff() how many objects are eligable for GC

answer is 1

can some one tell me which is the one object to be GC and how to work it out.

thanks very much.


ps: my understance is there will be only 5 objects created which are a1,b1, a2,b2. and alpha static instance, and the instance field in Alpha "Beta b2" will just inital to null when Alpha object is created. a1.b2 and a2.b2 are just references to object b1 and b2 respectively, therefore when a1 assign to null only object a1 is eligable to GC, am I correct?

[Wouter Oet]

Try to make a drawing for yourself with on one side the objects, the other side the references and in the middle arrows to connect the references with the objects. Then walk through the code and change the arrows. Once you're done you'll know which objects are eligible. But remember that Alpha.b2 is static.

[Ankit Garg]

This question has been discussed a lot of times before. See these threads

http://www.coderanch.com/t/481398/Programmer-Certification-SCJP/certification/many-eligible-gc
http://www.coderanch.com/t/474980/Programmer-Certification-SCJP/certification/Garbage-Collection-Clarification
http://www.coderanch.com/t/469606/Programmer-Certification-SCJP/certification/Garbage-Collection