package series01;

public class Stack<T> {

	private Node<T> top;


	public Stack() {
		top=null;
	}

	public boolean isEmpty() {
		return top==null;
	}



	public void push(T e) {
		Node<T> newTop = new Node<T>(e, null);
		if (top == null) {
			top = newTop;}
		else {
			top.next=top;
			top=newTop;
		}

	}

	public T pop() {

		if(isEmpty()) {
			throw new IllegalStateException();
		}

		T current = this.top.value;
		top=top.next;

		return current;

	}

	public T peek() {

		if(isEmpty()) {
			throw new IllegalStateException();
		}

		return top.value;

	}




}