package stacks;

public class NodeStack<E> implements Stack<E>{
	private Node<E> top; //reference to the head node
	private int size; //number of elements in the stack
	
	public NodeStack(){//constructs an empty stack
		top = null;
		size=0;
	}
	
	public int size(){return size;}
	
	public boolean isEmpty(){
		if (top==null) return true;
		return false;
	}
	
	public void push(E elem){
		Node<E> v=new Node<E>(elem,top); //create and link-in a new node
		top = v;
		size++;
	}
	
	public E top() throws EmptyStackException {
		if (isEmpty()) throw new EmptyStackException("Stack is empty.");
		return top.getElement();
	}
	
	public E pop() throws EmptyStackException {
		if (isEmpty()) throw new EmptyStackException("Stack is empty.");
		E temp = top.getElement();
		top=top.getNext(); //link-out the former top node
		size--;
		return temp;
	}
	
	//AM added the following methods, to be more like ArrayStack implementation

	public String toString(){
		String s;
		s="[";
		if (size()>0){Node temp=top;
			while (temp!=null){
				s=s+temp.getElement()+", ";
				temp=temp.getNext();
			}
		}
			s=s+"]";
			return s;
		}
		
	
	// Prints status information about a recent operation and the stack
	public void status(String op, Object element){
		System.out.print("------> " + op); //print this operation
		System.out.println(", returns " + element); //what was returned
		System.out.print("result: size = " + size() + ", isEmpty= " +isEmpty());
		System.out.println(", stack: " + this); //contents of the stack
	}
}