eligible for garbage collection

[rex tony]

Exercise
Question:
How many objects will be eligible for garbage collection after line 7?
public class TutorialGC
{
public static void main(String [] args)
{
Object a = new Integer(100); // Line1
Object b = new Long(100); // Line2
Object c = new String("100"); // Line3
a = null; // Line4
a = c; // Line5
c = b; // Line6
b = a; // Line7
// Rest of the code here
}
}
Choices:
� A. 0
� B. 1
� C. 2
� D. 3
� E. Code does not compile
Correct choice:
� B
[\code]
 
[code]
Explanation:
Among the three objects created in lines 1, 2, and 3, only the Integer object is eligible for
garbage collection at the end of line 7. The reference variable a, which originally referred to
the Integer object is made to refer to the String object in line 5. So the Integer object
is eligible for garbage collection after line 5, since there are no variables referring to it. The
variables b and c refer to the String and Long objects in lines 6 and 7, so they are not
eligible for garbage collection.
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Page 18 of 50 Java certification success, Part 1: SCJP

i can't understand any can explain this concepts?
Regards
Rex

[Pranav Bhatt]

Rex,
Here first at the time of creation
a refers to Integer object i.e a-> Integer Object
b refers to Long object i.e b-> Long Object
c refers to String object i.e a-> Sting Object

We will go now line by line-:

Line 4-: a-> null, so Integer Object is not being referenced by any references.

Line 5-: a refers to what c is refering
i.e a->String Object , c->String Object , b-> Long Object

Line 6-: c refers what b is refering so-:
c-> Long Object, b-> Long Object ,a-> still String Object

Line 7-: b refers to what a is refering so finally we land at
a-> String Object, b-> String Object and c-> Long Object

So only our Interger object has lost references to it. So eligible to GC.
I hope this clears it...