Java Variable Issue

public Entity(boolean hostile, String name, int hp, int def, int atk, int exp, int gold)
    {
        this.hostile = hostile;
        this.name = name;
        this.hp = hp;
        this.def = def;
        this.atk = atk;
        this.exp = exp;
        this.gold = gold;

        if (this.hp != 125) {
            oldName = this.name;
            oldHp = this.hp;
            oldAtk = this.atk;
            oldDef = this.def;
            oldExp = this.exp;
            oldGold = this.gold;
        }

public String toString()

    {
        return "\nA " + this.name.toUpperCase() + " HAS APPEARED!\n\n "
                + this.name + " HP: " + this.hp + "\n " + this.name + " DEF: "
                + this.def + "\n " + this.name + " ATK: " + this.randomATK + " ";

private static Random randomGenerator;
    private static ArrayList<Entity> hostiles;
    private static boolean gameStop = false;

    public static void main (String[] args)
    {
        hostiles = new ArrayList<Entity>();
        randomGenerator = new Random();

        hostiles.add(new Cyclops());
        hostiles.add(new Golem());
        hostiles.add(new Revenant());
        hostiles.add(new Vampire());
        hostiles.add(new Werewolf());
        hostiles.add(new Zombie());

        int index = randomGenerator.nextInt(hostiles.size());
        Entity entity = hostiles.get(index);
        Player player = new Player();
        player.gameStart();

        do {
                gameStop = true;
            player.gameStory();
            System.out.println(entity.toString());
            player.gameATK();

        } while (gameStop == false);

    }