Garbage collection

[H Singh]

At what stage in the following method does the object initially referenced by s becomes available for garbage collection. Select the one correct answer.


void method X() {
String r = new String("abc");
String s = new String("abc");
r = r+1; //1
r = null; //2
s = s + r; //3
} //4



Before statement labeled 1
Before statement labeled 2
Before statement labeled 3
Before statement labeled 4
Never.

Can someone explain what will be the answer to this question and why ?

[Srinivasa Raghavan]

My Answer is "Never".
To be more correct it's eligible for garbage collection after "methodX()" get's executed.

[Sisir Chanda]

yeahh..thats correct...because GC checkes whether the reference is being used anymore or not before doing garbage collection...since before line 4 the reference of s is being used so it will not be collected before the method returns.

[Joe Sondow]

I disagree. The correct answer is "Before statement labeled 4". The reason is that "the object initially referenced by s" is a String object with the value of "abc". In statement 3, a String object is created with the value "abcnull" and that String is then assigned to s. As a result, the "abc" String that used to be referenced by s is no longer referenced by anything, so the object initially referenced by s is eligible for garbage collection as soon as statement 3 completes, which is immediately before statement 4.

[amit taneja]

Originally posted by Sisir Chanda:
yeahh..thats correct...because GC checkes whether the reference is being used anymore or not before doing garbage collection...since before line 4 the reference of s is being used so it will not be collected before the method returns.

where u have read this about...
give me the linke....

i think joe sanawitz is perfectly right and i have seen that explanation every where but your statement is to be honest strange..

anyway give me the link from where you have read this..

[Sisir Chanda]

yep...It was my mistake...I read that the equestion is '...when the object refernced by s is eligible for GC...'. Since before line 4 , '....s = s + r; //3
...' was used, so my answer was s will never be eligible for GC. But the actual question was '....when the INITIAL object referenced by s will be eligible for GC.....'

The the answer is definitely....Before statement labeled 4. since at line 3 s has been assigned to a different object and s is referring to a different object. Having said that, the INITIAL object reference by s will become eligible for GC.

Thanks guys!!!