用applet实现了四种级别的贪吃蛇玩法。通过方向键控制蛇的动向，吃掉前面的食物，当碰到墙壁时，失败。-Using applet to achieve four levels of play Snake. Through the arrow keys to control the movements of the snake, eaten in front of the food, when it comes to walls, the failure.