doubt:garbage collection eligibility

[mansi gupte]

Hi all,

This question is from enthuware series.

After what line the MyClass object created at line 1 will be eligible for GC?

  class MyClass { }
public class TestClass
{
	MyClass getMyClassObject()
	{
1.		MyClass mc = new MyClass();
2.		return mc;
	}
	public static void main(String[] args)
	{
3.		TestClass tc = new TestClass();
4.		MyClass x = tc.getMyClassObject();
5.		System.out.println("got myclass object");
6.		x = new MyClass();
7.		System.out.printn("done");
	}
}

Select 1 correct option.
a 2


b 5


c 6
At line 6, x starts pointing to a new MyClassObject and there remains no reference to the original MyClass object.

d 7


e Never till the program ends.

How come the answer is c? can someone explain please?

thanks,
Piya

[Ankit Garg]

Lets see what the memory representation would be for this program

when line 1 is executed, this will be the memory representation

     mc
     |
     V
+------------+
| instance of|
|  my class  |
+------------+

now this same object is returned to main method. Since mc was local to getMyClassObject method, so it would no longer exist after the method body completes. This object will be caught by reference variable x so the memory representation would be

     x
     |
     V
+------------+
| instance of|
|  my class  |
+------------+

After this at line 6, x will start pointing to a new instance of MyClass and thus this object will have no reference to it

                           x
                           |
                           V
+------------+      +------------+
| instance of|      |  another   |
|  my class  |      | instance of|
+------------+      |  my class  |
                    +------------+

[Pawan Arora]

Before line 6, x variable has the reference of MyClass instance

see line 4:

MyClass x = tc.getMyClassObject(); 

But in line 6, a new variable has been assigned to it.

x = new MyClass();  

So, only one object is elligible for garbage collection.