LinkedStack.java

package Graphs;


/**
   A class of stacks whose entries are stored in a chain of nodes.

   @author Frank M. Carrano
   @author Timothy M. Henry
   @version 4.0
   UPDATED by C. Lee-Klawender
*/
public class LinkedStack<T> implements StackInterface<T>
{
	private Node topNode; // References the first node in the chain
	// ADD A PRIVATE INT FOR COUNTER THAT INDICATES HOW MANY NODES ARE IN THE STACK
	private int count=0;  // ADDED FOR EXERCISE 2.2*****************

	public LinkedStack()
	{
		topNode = null;
	} // end default constructor

	public boolean push(T newEntry)
	{
		topNode = new Node(newEntry, topNode);
		++count;  // ADDED FOR EXERCISE 2.2*****************
		return true;
	} // end push

	public T peek()
	{
		if (isEmpty())
			return null;
		else
			return topNode.getData();
	} // end peek

	public T pop()
	{
		T top = peek();
		if(topNode != null)
		{
			topNode = topNode.getNextNode();
			--count; // ADDED FOR EXERCISE 2.2*****************
		}
		return top;
	} // end pop

	public boolean isEmpty()
	{
		return topNode == null; // FINISH FOR EXERCISE 2.2
	} // end isEmpty

//  WRITE THE "MISSING" METHOD, REQUIRED FOR THIS CLASS SO IT'S NOT ABSTRACT (also Ex. 2.2):
	public int size(){ return count; }



	private class Node
	{
      private T    data; // Entry in stack
      private Node next; // Link to next node

      private Node(T dataPortion)
      {
         this(dataPortion, null);
      } // end constructor

      private Node(T dataPortion, Node linkPortion)
      {
         data = dataPortion;
         next = linkPortion;
      } // end constructor

      private T getData()
      {
         return data;
      } // end getData

      private void setData(T newData)
      {
         data = newData;
      } // end setData

      private Node getNextNode()
      {
         return next;
      } // end getNextNode

      private void setNextNode(Node nextNode)
      {
         next = nextNode;
      } // end setNextNode
	} // end Node



} // end LinkedStack