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 |
             +--------+
                 ^
                 |
     +-----------+--------------+
     |                          |
+--------+                  +-------+
|  Bull  |                  | Snake |
+--------+                  +-------+
|eating()|                  |eating()|
+--------+                  +-------+

             +--------+
             | Living |
             +--------+
             |toEating|
             +--------+

Animal.java

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

Bull.java

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

Snake.java

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

Living.java

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

测试代码：

public class Test {
    public static void main(String[] args) {
        Living living = new Living();
        Animal bull = new Bull();
        Animal snake = new Snake();
        living.toEating(bull, "草");
        living.toEating(snake, "老鼠");
    }
}

输出结果：

牛咀嚼草
蛇吞老鼠