Re: Singleton - Whether Cloneable overrides Singleton

From:

"Daniel Pitts" <googlegroupie@coloraura.com>

Newsgroups:

comp.lang.java.programmer

Date:

25 Mar 2007 23:48:31 -0700

Message-ID:

<1174891711.185555.292410@l75g2000hse.googlegroups.com>

On Mar 25, 11:43 pm, "Proton Projects - Moin"
<mohd.mohid...@gmail.com> wrote:

Hi all,

public class ChummaEx implements Cloneable
{
    private static ChummaEx moin = null;
    private String mName = null;
    private ChummaEx()
    {}

    public static ChummaEx getInstance()
    {
        if(moin == null)
        {
            createInstance();
        }
        return moin;
    }

    private static void createInstance()
    {
        if(moin == null)
        {
            moin = new ChummaEx();
        }
    }

    public void setName(String name)
    {
        mName = name;
    }

    public String getName()
    {
        return mName;
    }

    public static void main(String args[])
    {
        try
        {
         ChummaEx m1 = ChummaEx.getInstance();
         ChummaEx m2 = (ChummaEx)m1.clone();
            System.out.println(System.identityHashCode(m1));
            System.out.println(System.identityHashCode(m2));
            m1.setName("Moin");

            System.out.println(m2.getName());
            System.out.println(m1.getName());
        }
        catch(CloneNotSupportedException e)
        {
            System.out.println("In Catch");
            e.printStackTrace();
        }
    }

}

Output :

11394033
4384790
null
Moin

SIngleton has the functionality to create only instance...I was trying
to beak the singleton behavior and after a long research i achieved it
by using the Cloneable interface...

My Questions are:
1. Whether the singleton behavior is overriden by the Cloneable
behavior
2. By implementing the Cloneable interface, how to retain the
Singleton behavior...
3. I tried to use the final key at some place to retain the singleton
behavior....but i failed.
4. Some group mates might have a question in their mind, why i have
used the Cloneable interface....as i already told, i was doing some
research over the singleton...

Kindly help me in this regard
Thanks
Moin

You have to take steps toward making classes into singletons. One of
those steps is to prevent the use of Cloneable. Also, if your
singleton is serializable, you'll have to consider that as well.

public final class MySingleton implements Serializable {
  public static final MySingleton instance = new MySingleton();

  private MySignleton() {
  }

  protected final Object clone() throws CloneNotSupportedException {
     throw new CloneNotSupportedException();
  }
  protected final Object readResolve() {
    return instance;
  }
}