Stack

import org.w3c.dom.Node;

public class Stack<T> {
    private Node head;
    private int count;
    private Node tail;

    //Retorna cantidad de elementos de la lista
    public int getCount() {
        return this.count;
    }
    public Stack() {
        this.head = null;
        this.count = 0;
        this.tail = null;
    }
    //agreg al principio
    public void AddFirst(T item) {
        Node temp = new Node(item, this.head);
        if(this.count==0) {
            this.tail=temp;
        }
        this.head=temp;
        ++this.count;
    }
    //agrega al final
    public void AddLast(T item) {
        Node temp=new Node(item,null);
        if(this.count==0) {
            this.head=temp;
        }else {
            this.tail.next=temp;
        }
        this.tail=temp;
        ++this.count;
    }
    //exttrae y devuelve el primer elemento
    public T RemoveFirst() {
        if(this.count==0) {
            throw new RuntimeException("La lista esta vacia...");
        }
        T item =this.head.item;
        this.head=this.head.next;
        if(this.head==null) {
            this.tail=null;
        }
        --this.count;
        return item;
    }
    //extrae y devuelve el ultimo elemntoo de la lista
    public T RemoveLast() {
        if(this.count==0) {
            throw new RuntimeException("La lista esta vacia...");
        }
        T item = this.tail.item;
        if(this.head.next==null) {
            this.head=this.tail=null;
        }else {
            Node skip=this.head;
            for(;skip.next.next != null;skip=skip.next) { }
            this.tail=skip;
            this.tail.next=null;
        }
        --this.count;
        return item;
    }
    public void Mostrar() {
        for (Node skip=this.head;skip != null;skip=skip.next) {
            System.out.printf("%s", skip.toString());
        }
    }
    private class Node{
        public T item;
        public Node next;
        public Node() {
            this(null,null);
        }
        public Node(T item) {
            this(item,null);

        }
        public Node(T item,Node next) {
            this.item=item;
            this.next=next;
        }
        public String toString() {
            return this.item.toString();
        }
    }

}