How to destroy Singleton Object ?

[Ashwin Kumar]

Can anybody tell me how to destroy Singleton Object with out closing the application ??

[James Carman]

You could use a clear() method...

  
public class Singleton
{
  private static Singleton instance;
 
  public Singleton getInstance()
  {
    if( instance == null )
    {
      instance = new Singleton();
    }
    return instance;
  }
 
  public void clear()
  {
    instance = null;
  }
}

[Roger Chung-Wee]

You cannot destroy an object, only the JVM can do that.

Once an object is inaccessible by any live threads, it then becomes eligible for garbage collection.

[David O'Meara]

Sounds like something which possibly shouldn't be a Singleton.

You can unload a Class by removing any references to its ClassLoader and allowing both to be garbage collected. It's easier to redesign the Class so this isn't required though.

Dave

[Ilja Preuss]

I agree with Dave - sounds like you probably shouldn't use the Singleton pattern.

[David O'Meara]

Although James' solution works. If that's what you need you'd probably better with a factory to hand out the various instances - ie not a Singleton.

[Geoffrey Falk]

The clear() idea will not work, because some other class may have already obtained a reference. Then if it is cleared, the next caller will get a different instance and you will have two instances of your "Singleton".

There is no way to destroy a Singleton without breaking the Singleton property.

Geoffrey

[Ryan McGuire]

As others have said, maybe a Singleton isn't appropriate here. If the number of instances of the class can go down to zero, then it's not a Singleton.

Instead of destroying the existing object and instantiating a new one, could you just change the internal state of the one that already exists? Or would that mess up any client objects that already have a reference to it?

What is this class/object used for?

Ryan

[Stan James]

What behavior do you expect? How would you know that it's been destroyed? What would happen?

I kinda liked James Carman's first response that when you ask for the instance you get nothing. That's a sign that it's no longer there even though it may be in memory a while before GC. If you had to load it from the class file again for some reason you could just use a new classloader (maybe a custom one) and populate your "theOnlyInstance" variable again.

[Henry Wong]

Here's an interesting option... For the clear() method, move the instance to a weak reference. When the factory is called, it can try to get the reference back first. If it can't, then it can create a new one.

Henry