public class LinkedStack<T> implements StackInterface<T>  {
 
 private Node topNode;
 
 public LinkedStack(){
  topNode = null;
 }
 
 public void push(T newEntry){
  
  Node newNode = new Node (newEntry, topNode);
  topNode = newNode;
  
 }
 
 public T peek(){
  T top = null;
  if(topNode != null)
   top = topNode.getData();
  return top;
 }
 
 public T pop(){
  T top = null;
  if(topNode != null)
   topNode = topNode.getNextNode();
  return top;
 }
 
 public boolean isEmpty(){
  return topNode == null;
 }
 
 public void clear(){
  topNode = null;
 }
 
 
 private class Node implements java.io.Serializable{
  
  private T data;
  private Node next;
  
  private Node(T dataPortion){
   
   data = dataPortion;
   next = null;
  }
  
  private Node(T dataPortion, Node linkPortion){
   data = dataPortion;
   next = linkPortion;
  }
  
  private T getData(){
   return data;
  }
  
  private void setData(T newData){
   data = newData;
  }
  
  private Node getNextNode(){
   return next;
  }
  
  private void setNextNode(Node nextNode){
   next = nextNode;
  }
  
  
 }

}