Problem with SingleTon

[jami siva]

Hi,

When I am trying to develop singleton class, It is not behaving like Singleton class.
Please check where I did wrong.
This is my SingleTon class.

public class SingleTon {
	private static SingleTon singleTon = null;
	private static int count = 0;
	private SingleTon() {
		
	}
	
	static SingleTon getSingleTon() {
		if (singleTon == null) {
			count++;
			return new SingleTon();
		} else {
			return singleTon;
		}
	}
	
	static void instanceCount() {
		System.out.println("Instance "+count);
	}
}

To test this singleton i wrote this class,

public class TestSingleTon {
	public static void main(String[] args) {
		TestSingleTon obj1 = new TestSingleTon();
		obj1.mOne();
		obj1.mTwo();
	}
	void mOne() {
		SingleTon  s = SingleTon.getSingleTon();
		System.out.println("SingleTon Obj>>"+s);
		s.instanceCount();
	}
	
	void mTwo() {
		SingleTon  s = SingleTon.getSingleTon();
		System.out.println("SingleTon Obj>>"+s);
		s.instanceCount();
	}
}

After the result it is printing below output. But i expeced Instance is always 1 and object is same.
SingleTon Obj>>SingleTon@19821f
Instance 1
SingleTon Obj>>SingleTon@addbf1
Instance 2

[Jeff Verdegan]

Where are you setting your member variable to be non-null? In other words, how do you think you'll ever get into the else block in

if (singleTon == null) {
  count++;
  return new SingleTon();
} else {
  return singleTon;
} 

Also, when posting code, please UseCodeTags(⇐click) so it will be readable.

And, finally, while this may be a useful academic exercise, the problem you're having only comes about because you're doing lazy instantiation. There is no good reason to do that. Simply instantiate at declaration time.

pubic class MySingleton {
  private static final MySingleton instance = new MySingleton();

  private MySingleton() {
  }

  public static MySingleton getInstance() {
    return instance;
  }
}

Or else just use the enum singleton approach.

[dennis deems]

If you really want singleton behavior, one of the first things you need to do is prevent the class from being instantiated by any other class.

[jami siva]

Thank Guys for your reply.

But If I do like this there is no singleton object, right?
Share your suggestions.

singletTonObj.clone();

[Matthew Brown]

Try it. As long as you haven't implemented Cloneable it won't work. And by default clone() is protected.

[Winston Gutkowski]

jami siva wrote:But If I do like this there is no singleton object, right?
singletTonObj.clone();

Depends on how you implement clone(); but if you think about it, the call is nonsensical.

Winston