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garbage collection

maggie karve
Ranch Hand
Posts: 187
How many objects are eligible for garbage collection after executing line 7?
view source print

public class Tester {

public static void main(String[] args) {

Integer x = new Integer(3000);

Integer y = new Integer(4000);

Integer z = new Integer(5000);
Object a = x;

x = y;

y = z;

z = null; //line 7

}

}here the answer is zero i don know how..anybody kindly explain..according to me the answer should be 3...

Neha Daga
Ranch Hand
Posts: 504
how 3? 0 is correct

Raju Champaklal
Ranch Hand
Posts: 521
the answer is zero...after line 7 a refers to the first first object....x to 2nd....y to 3rd...so everyone has a reference

W. Joe Smith
Ranch Hand
Posts: 710
curve karve wrote:How many objects are eligible for garbage collection after executing line 7?
view source print

public class Tester {

public static void main(String[] args) {

Integer x = new Integer(3000);

Integer y = new Integer(4000);

Integer z = new Integer(5000);
Object a = x;

x = y;

y = z;

z = null; //line 7

}

}here the answer is zero i don know how..anybody kindly explain..according to me the answer should be 3...

Ok, I set up a little graph, lets see if I can recreate it:

Three objects are created. For ease, I call them ojb1, obj2, obj3, in order of creation. Left column is the objects, right is the variable referencing them, through the line Object a = x:

Objects|references
obj1 |x,a
obj2 |y
obj3 |z

Now we assign x the same reference as y, so our graph changes to this:

Objects|references
obj1 |x,a
obj2 |y,x
obj3 |z

Now we assign y the same reference as z, so our graph changes to the following:

Objects|references
obj1 |x,a
obj2 |y,x
obj3 |z,y

Now we assign z null, so our graph changes to the following:

Objects|references
obj1 |x,a
obj2 |y,x
obj3 |z,y

Even though z is pointing to nothing, all created objects have active references. Therefore, none of them are eligible for GC.

Phungsuk Wangdu
Ranch Hand
Posts: 114
yep right zero is right 3 is wrong everyone has a reference

well that graph thing is really great can be used to solve any GC question thanks for it W.Joe Smith

Minhaj Mehmood
Ranch Hand
Posts: 400

HTH

Minhaj

W. Joe Smith
Ranch Hand
Posts: 710
Mahesh Chitale wrote:yep right zero is right 3 is wrong everyone has a reference

well that graph thing is really great can be used to solve any GC question thanks for it W.Joe Smith

There are other ways to do it, especially with really complicated GC problems, but this one was simple enough that my graph worked well

Phungsuk Wangdu
Ranch Hand
Posts: 114
well can you tell us the other methods which may be requied in SCJP
because these GC questions are really a headache

maggie karve
Ranch Hand
Posts: 187
hey thanks i got it....