抽象类练习： 不同动物进食的方式不同，例如蛇吞，牛咀嚼。（1）定义抽象的动物类Animal，包含抽象方法eating（String food）方法；(2)定义动物子类牛、蛇等，重写父类动物的eating()方法实现不同动物不同的进食方式;(3)定义Living类，定义方法toEating(Animal animal,String food)，测试不同动物的进食方式。测试结果如图所示。要求先画出类结构图，然后编写Java程序。

类结构图如下：

          +--------------+
          |    Animal    |
          +--------------+
          | + eating()   |
          +--------------+
                  ^
                  |
          +--------------+
          |    Snake     |
          +--------------+
          | + eating()   |
          +--------------+
                  ^
                  |
          +--------------+
          |     Cow      |
          +--------------+
          | + eating()   |
          +--------------+
                  ^
                  |
          +--------------+
          |    Living    |
          +--------------+
          | + toEating() |
          +--------------+

代码实现如下：

// Animal.java
public abstract class Animal {
    public abstract void eating(String food);
}

// Snake.java
public class Snake extends Animal {
    @Override
    public void eating(String food) {
        System.out.println("蛇吞" + food);
    }
}

// Cow.java
public class Cow extends Animal {
    @Override
    public void eating(String food) {
        System.out.println("牛咀嚼" + food);
    }
}

// Living.java
public class Living {
    public void toEating(Animal animal, String food) {
        animal.eating(food);
    }
}

// Main.java
public class Main {
    public static void main(String[] args) {
        Living living = new Living();
        Animal snake = new Snake();
        Animal cow = new Cow();

        living.toEating(snake, "老鼠");
        living.toEating(cow, "草");
    }
}

运行结果如下：

蛇吞老鼠
牛咀嚼草