public void addApple() {
    accomplishedSnake = false;
    accomplishedApples = false;
    while(!accomplishedSnake && !accomplishedApples) {
        xApple = 20 * MathUtils.random(0, 23);
        yApple = 20 * MathUtils.random(0, 39);
        for(int i=0; i<snake.getSize(); i++) {
            if(snake.getPart(i).getX() == xApple && yApple == snake.getPart(i).getY())
                break;
            if(i == snake.getSize()-1) {
                accomplishedSnake = true;
                break;
            }
        }
        for(int i=0; i<apples.size; i++) {
            if(apples.get(i).getX() == xApple && yApple == apples.get(i).getY())
                break;
            if(i == apples.size-1) {
                accomplishedApples = true;
                break;
            }
        }
    }
    apples.add(new Apple(xApple, yApple));
}