Implementation With only one SubClass

How can we make Singleton with subClass
The following implementation ensure there is only SubClass instance.

1. Create abstract SuperClass // forbid initiate




1. create protected instance field // only access by subclass


2. create protected constructor // only access by subclass


3. create public access to instance field //




2. defien subclassol
   
   
   
   1. create private constructor // only access by subclass
   
   
   2. override public method to access to instance field //
   
   
   
   

public abstract SuperClass{
    protected static SuperClass instance=null;
       protected SuperClass(){
         // interface to subclass
       }//:f
    public static SuperClass(){
       return instance;
    }//:f
}//:c
public SubClass1 extends SuperClass{
    private SubClass1(){
      //prevent initiation
    }//:f
    public static SuperClass(){
       if(instance==null){
           instance=new SubClass1();
       }//:if
    }//:f
}//:c