when is eligible for garbage collection?

[eric lee]

can someone give me a concept and answer the below question? Thanks.
When is the Integer object created in line 3, which line eligible for garbage collection?
1. class m {
2. public Object m () {
3. object o = new Integer (10);
4. object [] oa = new object [1];
5. oa[0]= o;
6. o = null;
7. return oa[0];
8. }
9. }

[Don Bosco]

The Integer object created in line 3 is not eligible for gc in the m() method. This is bcos line 7 is returning a reference to this object.

1 class m {
2 public Object m () {
3 object o = new Integer (10);
4 object [] oa = new object [1];
5 oa[0]= o;
6 o = null;
7 return oa[0];
8 }
9 public static void main(String s[]){
10 m m1 = new m();
11 Object o = m1.m;
12 o = "Don Bosco";
}
}

In the above code, the object created in line 3 is eligible for gc in line 12.

[eric lee]

Hi,Don Bosco,how about line 6, is line 6 eligible
for garbage collection? (o=null),thanks
1 class m {
2 public Object m () {
3 object o = new Integer (10);
4 object [] oa = new object [1];
5 oa[0]= o;
6 o = null;
7 return oa[0];
8 }
9 public static void main(String s[]){
10 m m1 = new m();
11 Object o = m1.m;
12 o = "Don Bosco";
}
}

[Don Bosco]

Originally posted by eric lee:
Hi,Don Bosco,how about line 6, is line 6 eligible
for garbage collection? (o=null),thanks
1 class m {
2 public Object m () {
3 object o = new Integer (10);
4 object [] oa = new object [1];
5 oa[0]= o;
6 o = null;
7 return oa[0];
8 }
9 public static void main(String s[]){
10 m m1 = new m();
11 Object ob = m1.m;
12 ob = "Don Bosco";
}
}

o and oa[0] both point to same OBJECT before line6.
at line6 o is made to point null. but since oa[0] still points to that OBJECT, the OBJECT is not eligible for garbage collection.
remember that garbage collection is done on OBJECTS, not on references.
[ December 03, 2002: Message edited by: Don Bosco ]

[eric lee]

Hi Don:
so the line 5 is eligible for garbage collection?
Do i correct? Thanks.
class test {
public static void main(String args[]){
1. String myString = new String("Batman");
2. String mySecond = new String("Robin");
3. System.out.println(myString + mySecond);
4. myString = null;
5. myString = mySecond;
6. mySecond = null;
}
}

[Don Bosco]

After line 4, the object created in line 1 is eligible for gc.

[eric lee]

Hi,Don Bosco,i get a little clear now,can you give me one more example for gc like garbage collection is done on OBJECTS, not on references.
by the way, you said that after line 4 ,so the answer is line 5 for gc correct? Thanks.