memory leaks in Java

[Navatha]

Hi All ,
Can you tell me .when we will have memory leaks in java.And how to avoid the memory leaks in java.

Thanks in Advance
Navatha

[Norm]

One sort of memory leak is an object that isn't being used but still has a reference to it being held somewhere. For example unused listeners can often be left attached when they should have been removed.
Avoid by good programming practices. If you open a file, close it. If you add a listener, remove it.

[Navatha]

Is this the only type of memory leak or there are any other type of memory leaks.One method is using garbage collection .The other one is as you said Norm. What type of memory leaks we encounter with collections.
Thanks in advance
Navatha

[Zack]

Garbage collection is not a method of creating memory leaks. Garbage collection removes unused blocks of memory so that memory does NOT leak.

How does garbage collection work?

[JosAH]

Garbage collection is not a method of creating memory leaks.

Have a look at this one:

import java.util.ArrayList;
import java.util.List;

public class Leak {
	private static List<Leak> zombies= new ArrayList<Leak>();
	
	protected void finalize() {
		zombies.add(this);
	}
}

kind regards,

Jos

[Tolls]

The solution to that is to never write stuff in a finalize()...:)
That really is a red flag warning during a code review.

[Zack]

Agreed with Tolls. That's not the garbage collector's fault, that's a bad coder's fault. ;)

[masijade]

You'd be surprised, however, how often people use finalize, though. And i almost always leads to these types of problems.

[JosAH]

Agreed with Tolls. That's not the garbage collector's fault, that's a bad coder's fault. ;)

It's called 'resurrection' and the JVM's weak defense against it is to call those finalizer methods only once by the gc; but I agree: finalizers are not of much use (except for resource deallocation (if it isn't too late yet)).

kind regards,

Jos