Pilas

Interfaz a utilizar

package Pila;

/**
 * @author Daniel Cataño Restrepo
 */
public interface IPila<E&gt{
    public boolean isEmpty();
    public E peek();
    public E pop();
    public void print();
    public void push(E target);
}

La clase Pila

package Pila;
/**
 * @author Daniel Cataño Restrepo <dasniel199410@gmail.com>
 */
public class Pila<E> implements IPila<E>{
    E[] data;
    
    public Pila(){
        data=(E[])new Object[0];
    }
    
    public boolean isEmpty() {
        return data.length==0;
    }

    public E peek() {
        return data[0];
    }
    
    /**
     * Remueve el primer elemento de la pila, y lo retorna
     */
    public E pop() {
        E firstElement=data[0];
        E[] temp=(E[])new Object[data.length-1];
        for(int i=0; i<data.length-1; i++)
            temp[i]=data[i+1];
        data=temp;
        return firstElement;
    }

    public void print() {
        System.out.print("[");
        for(int i=0; i<data.length; i++){
            if(i==data.length-1)
                System.out.print(data[i]);
            else
                System.out.print(data[i]+", ");
        }
        System.out.println("]");
    }
    
    /**
     * Agrega un nuevo elemento a la pila
     */
    public void push(E target) {
        E[] temp=(E[])new Object[data.length+1];
        for(int i=data.length-1; i>=0; i--){
            temp[i+1]=data[i];
        }
        temp[0]=target;
        data=temp;
    }
}

La clase Principal

package Pila;

/**
 * @author Daniel Cataño Restrepo <dasniel199410@gmail.com>
 */
public class Main {
    
    public static void main(String[] args) {
       Pila p=new Pila();
       p.push(1);
       p.push(2);
       p.push(3);
       p.push(4);
       p.push(1);
       p.push(2);
       p.push(3);
       p.push(4);
       p.print();
       p.pop();
       p.pop();
       p.pop();
       p.pop();
       p.print();
    }
}