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