Object being garbage Collected by programmer or by JVM

[Ravi Kiran Va]

Hi

Please tell me who makes Garbage Collection .

IF i have a Object for example a Connection Object in JDBC with instance name as conn.

IF i say conn==null.


with this line conn==null

is the programmer making the Garbage collection ??

Or this will help JVM to make the conn Object Garbage Collected ??

share your knowledge .

Thanks in advance .

[marc weber]

Removing all references to an object (setting those variables to null) will make that object eligible, but there's no guarantee it will be collected while the program is running.

You can't force or guarantee garbage collection. (Note that calling System.gc() only "suggests that the Java Virtual Machine expend effort toward recycling unused objects.")

[sujith Acharya]

when you say conn=null, then its an indication to JVM is that, the object which conn is pointing is eligible for garbage collection(provided there no other reference to that object)

[Wouter Oet]

Objects are garbage collected when no live thread can access then. One way of achieving that is by nulling all the references to that object.
But that doesn't work always:

public class Test
{
	Test a;
	
	public static void main(String args[]) {
		Test a = new Test();
		Test b = new Test();
		Test c = new Test();
		a.a = b;
		b.a = c;
		c.a = a;
		
		a = null;
		b = null;
		c = null;
		
		System.out.println("Start");
		System.gc();
		try
		{
			Thread.sleep(2000); // Give some free time to gc
		} catch(InterruptedException ie){}
		System.out.println("End");
	}
}

There are still references to the Test objects however no live thread can access them. The JVM recognizes these Islands of Objects and GC'd them.
Run:

wouter@wouter-laptop:~/temp$ javac Test.java
wouter@wouter-laptop:~/temp$ java -verbose:gc Test
Start
[GC 232K->120K(32256K), 0.0009260 secs]
[Full GC 120K->103K(32256K), 0.0037630 secs]
End

[Siva Masilamani]

By making reference to null, you are telling JVM that i do not need this object anymore and you may garbage collect it at your own convenient time unless the no more reference is given to this object else where(this includes finalized method).

[David Newton]

Wouter Oet wrote:Objects are garbage collected when no live thread can access then.

Well, not necessarily--that's when they're *eligible*, but not necessarily when they're actually collected.

[Ravi Kiran Va]

Thank you all , for sharing knowledge.