how java singleton can extends other classes?

public class Singleton extends Parent{
  private Ui ui;
  private Store store;

  // Static field to hold the singleton instance 
  private static final singleton INSTANCE;

  // This is a static constructor. It will be executed once, when the class is 
  // loaded.  Use this to create an instance of your class for the singleton
  static {

     INSTANCE =  new Singleton(Ui.getInstance(), Store.getInstance());
  }

  // This is the constructor. You HAVE to pass the parameters to the base 
  // class (Parent), See the static constructor above.
  private Singleton(Ui ui, Store store) {
      super(ui, store);
  }

  public static singleton getInstance() {

      return INSTANCE;
  }
 
  protected Object readResolve() {

      return getInstance();
  }

  public void SetStore(Store dstore){

      store = dstore;
  }

  public void SetUi(Ui uid){

      ui = uid;
  } 
}