sample

import java.util.ArrayList;
import java.util.LinkedList;

public class Main {

    public static void main(String[] args) {


        MyStack s = new MyStack();

    }
}

class Person {

    private static final int DEAD_AGE = 100;

    int age;
    String name;

    public Person(String name) {
        this.name = name;
    }

    public void birthday(){
        System.out.println("Happy birthday");
        if (age < DEAD_AGE)
            age++;
    }

    public void makeBaby() {
        age = 0;
    }
}

abstract class Weapon {

    private String name;
    protected int range, speed, power, rechargeTime;

    public Weapon(String name) {
        this.name = name;
    }

    public abstract void fire();
}

class BFG extends Weapon {
    public BFG() {
        super("BFG");
        range = 100;
        speed = 1;
        power = 1000;
        rechargeTime = 2;
    }

    public void fire(){
        System.out.println(power + " * Kaboom !");
    }

    public void bfgKillAll(){
        System.out.println("BFG extra juice");
    }
}

public class Hero {
    private Weapon hpn;
//    composition
    private String name;

    public Hero(String name) {
        this.name = name;
    }

    public void shoot() {
//        delegation
        hpn.fire();
    }
}

class MyStack extends LinkedList {

    public boolean isEmpty(){
        return isEmpty();
    }

    public void push(Object o) {
        add(o);
    }

    public Object pop(){
        return removeLast();
    }
}