Double K&B Chapter 3- Question 11

[Prithvi Sehgal]

Dear All,
This is an exercise question from K&B and i have a doubt.

 
class Beta{}
class 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 ;
		a2.b2 = b1 ;
		a2.b2 = b2 ;
		
		a1 = null;
		b1 = null ;
		b2 = null;
		

		
	}
	
}

To my knowledge, there should be two objects eligible for garbage collection. a1 and b1, but book says only one object is eligible for
garbage collection. Exact explanation is written like this

It should be clear that there is still a reference to the object referred to by a2, and that there is still a reference to the object referred by
a2.b2. What might be less clear is that you can still access the other Beta object through the static variable a2.b1, because its static.

Why a2.b1 is an object? It should be a reference variable having null because we never initialized the value of a2.b1. By default when it is
initialized it will be having a value of null.

Please clarify.

Thanks,

[Henry Wong]

Hint: take a look at line 4 of your post.

[Prithvi Sehgal]

I am unable to understand still why only one object is eligible for garbage collection.
What about objects b1 and b2 in main? Please can someone explain me this problem
and this static reference field. I am confused.

[Ankit Garg]

This question has been asked many times before. Search the forum for "alpha beta", you'll find discussions like the following

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

[Prithvi Sehgal]

Thanks Ankit.

Understood it. Very minor mistake i was making, will take care in future.

Best Regards,