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GC ... Explain Code....

 
Greenhorn
Posts: 12
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A progmmer has written the following class to prevent garbage collection of the objects of this class. Is he mistaken?

class SelfReferencingClassToPreventGC
{
private SelfReferencingClassToPreventGC a;
Object obj = new Vector();
public SelfReferencingClassToPreventGC()
{
a = this; //reference itself to make sure that this is not garbage collected.
}

public void finalize()
{
System.out.println("Object GCed");
}
}


Answer provided :

Explanation:
Yes, he is definitely mistake. Because, all he is creating is a circular reference, but such references do not prevent an object from garbage collection. Basically, if B is only refereded to by A and A is eligible for GC, then B iseligible for GC to. So, if A refers to B and B refers back to A, this arrangement does not prevent them from being garbage collected

Could anyone explain the actual concept ..
 
Ranch Hand
Posts: 252
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Hema..refer to island of isolation objects in KnB ..nice explanation was given ..
 
Ranch Hand
Posts: 99
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GC Rule:

Collect any objects which are not reachable by any part of code. Try the below...

import java.util.*;

class SelfReferencingClassToPreventGC
{
private SelfReferencingClassToPreventGC a;
Object obj = new Vector();
public SelfReferencingClassToPreventGC()
{
a = this; //Cyclic Reference !!!. But this cant stop the object from being garbage collected.
}

public void finalize()
{
System.out.println("Object GCed");
}
}

class SimpleGCThread extends Thread
{
public void run()
{
System.out.println("I will collect the objects which are not reachable by any code");
while (true)
{
System.gc();
try
{
Thread.sleep(100);
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
}
class GCTester {

void aMethod()
{
SelfReferencingClassToPreventGC aObj = new SelfReferencingClassToPreventGC();
}

public static void main (String args []) {
new GCTester().aMethod();
SimpleGCThread gcThread = new SimpleGCThread();
gcThread.start();

}
}
 
Greenhorn
Posts: 20
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hi,Lakshmanan
Look the follow code that i modified you code a litter .but can let everybody see lightly when and why the gc working.
import java.util.*;

class SelfReferencingClassToPreventGC
{
private SelfReferencingClassToPreventGC a;
Object obj = new Vector();
public SelfReferencingClassToPreventGC()
{
a = this; //Cyclic Reference !!!. But this cant stop the object from being garbage collected.
}

public void finalize()
{
System.out.println("SelfReferencingClassToPreventGC Object GCed");
}
}

class SimpleGCThread extends Thread
{
private SelfReferencingClassToPreventGC s ;
public void run()
{
System.out.println("I will collect the objects which are not reachable by any code");
while (true)
{
System.gc();
try
{
Thread.sleep(100);
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
public void setInstance(SelfReferencingClassToPreventGC sgc){
s = sgc;
}
public void finalize()
{
System.out.println("SimpleGCThread Object GCed");
}
}
class GCTester {

SelfReferencingClassToPreventGC aMethod()
{
SelfReferencingClassToPreventGC aObj = new SelfReferencingClassToPreventGC();
return aObj;
}

public static void main (String args []) {
SelfReferencingClassToPreventGC sgc = new GCTester().aMethod();
SimpleGCThread gcThread = new SimpleGCThread();

gcThread.setInstance(sgc);//if commented ,sgc will garbage collected.

gcThread.start();

}
}
 
Lakshmanan Arunachalam
Ranch Hand
Posts: 99
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Hi enter,

Thanks for your input.

I modified the main method to have more FUN ))
 
Don't get me started about those stupid light bulbs.
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