Lecture 7 - slide 19 : 41

class DoubleLinkable extends Linkable {

   private DoubleLinkable prev;
   
   public DoubleLinkable(){
     super();
     prev = null;
   }

   public DoubleLinkable(Object data){
     super(data);
     this.prev = null;
   }


   public DoubleLinkable(Object data, Linkable next){
     super(data,next);
     this.prev = null;
   }

   public DoubleLinkable(Object data, Linkable next, DoubleLinkable prev){
     super(data,next);
     this.prev = prev;
   }

   public Linkable prev(){
     return(prev);
   }

   public void setPrev(DoubleLinkable prev){
     this.prev = prev;
   }

 } // end DoubleLinkable