Creating your Own Marker Interface

Here we are going to Create our own marker Interface."SingleTon". If any class implements this interface,then its object will be created only 1 time.
Folder Structure

SingleTon.java 

public interface SingleTon

{

}

FrameWorkContainer.java

import java.lang.reflect.Constructor;
import java.util.HashMap;                 
                                                            
class FrameWorkContainer               
{                                                          
static Object obj=null;                       

//HashMap will Only store those objects whose class has implemented SingleTon interface
static HashMap hmap=new HashMap();

public static Object createObject(Class cls)
 {
    //Get the Exact className,from cls
    String objName=cls.getCanonicalName();
     try
     {//get access to constructor and make it accessible
      Constructor construct=cls.getDeclaredConstructor();
      construct.setAccessible(true);
      //if hmap doesnot contain object with this key,create the object,
      //and store it in hashmap only if that object has implemented SingleTon interface
      //If the object has not implemented singleton,simple return the object without storing in hashmap
   
      if(!hmap.containsKey(objName))
      {
          obj=construct.newInstance();
          if(obj instanceof SingleTon )
              hmap.put(objName, obj);
          return obj;
      }
      else //if hashMap contains that object,return that object
      {   
            obj=hmap.get(objName);
            return obj;
      }
     
     
     }catch(Exception e){return null;}
   
}
}

Client.java 
------------

public class Client
{
    public static void main(String[] args)
    {       
        //Test class has implemented Singleton interface
        Test t1=(Test)FrameWorkContainer.createObject(Test.class);
        Test t2=(Test)FrameWorkContainer.createObject(Test.class);
        Demo d1=(Demo)FrameWorkContainer.createObject(Demo.class);
        Test t3=(Test)FrameWorkContainer.createObject(Test.class);
        Demo d2=(Demo)FrameWorkContainer.createObject(Demo.class);
        t1.sayHello();
       
        System.out.println(t1.hashCode());
        System.out.println(t2.hashCode());
        System.out.println(t3.hashCode());
        System.out.println(d1.hashCode());
        System.out.println(d2.hashCode());
      }
}

Demo.java
------------

public class Demo  
{
    private Demo(){}
}

Test.java
--------------------------------------------------------------------------------------------------------
public class Test implements SingleTon
{
    private Test(){System.out.println("Constructor::Test");}
    public void  sayHello()
    {
        System.out.println("Test::sayHello()");
    }
}