这个练习我用到了继承，多态和封装。

1.继承：
Animal 类是一个抽象类，它有两个子类 Dog 和 Cat。
Dog 和 Cat 分别继承自 Animal 类，因此它们可以使用 Animal 类中定义的属性和方法，同时也可以有自己特有的属性和方法。

2.多态：
在 Person 类的 keepPet 方法中，通过 instanceof 关键字判断传入的动物对象是 Dog 还是 Cat 类型，然后进行相应的操作。这就是多态的体现，即相同的方法调用可以根据不同对象的实际类型执行不同的操作。

3.封装：
Animal 类中的 color 和 age 属性被设置为私有（private），只能通过公共的 getter 和 setter 方法访问和修改。

package com.animal.java;public abstract class Animal {private String color;private int age;public Animal() {}public Animal(String color, int age) {this.color = color;this.age = age;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public abstract void eat(String str);}

package com.animal.java;public class Dog extends Animal{public Dog() {}public Dog(String color, int age) {super(color, age);}public void lookHouse(){System.out.println("小狗正在看家");}@Overridepublic void eat(String str) {System.out.println(getAge() + "岁的" + getColor() + "小狗正在猛吃" + str);}
}

package com.animal.java;public class Cat extends Animal{public Cat() {}public Cat(String color, int age) {super(color, age);}public void catchMouse(){System.out.println( getColor() +"的猫正在抓小老鼠");}@Overridepublic void eat(String str) {System.out.println(getAge() + "岁的" + getColor() + "小猫正在吃" + str);}}

package com.animal.java;public class Person {private String name;private int age;public Person() {}public Person(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}/**饲养狗public void keepPet(Dog dog,String str){System.out.println("年龄为" + this.age + "岁的" + this.name + "养了一只年龄为" +dog.getAge() +"岁的" + dog.getColor() +"小狗");dog.eat(str);}饲养猫public void keepPet(Cat cat,String str){System.out.print("年龄为" + this.age + "岁的" + this.name + "养了一只年龄为" +cat.getAge() +"岁的" + cat.getColor() +"小猫");cat.catchMouse();}*/public void keepPet(Animal animal,String str) {if(animal instanceof Dog){Dog dog = (Dog) animal;System.out.println("年龄为" + this.age + "岁的" + this.name + "养了一只年龄为" +dog.getAge() +"岁的" + dog.getColor() +"小狗");dog.eat(str);}else if(animal instanceof Cat){Cat cat = (Cat) animal;System.out.println("年龄为" + this.age + "岁的" + this.name + "养了一只年龄为" +cat.getAge() +"岁的" + cat.getColor() +"小猫");cat.eat(str);}else {System.out.println("没有这种动物");}}
}

package com.animal;import com.animal.java.Animal;
import com.animal.java.Cat;
import com.animal.java.Dog;
import com.animal.java.Person;public class Test {public static void main(String[] args) {Person person1 = new Person("老王",30);Animal dog = new Dog("黑色",2);person1.keepPet(dog,"骨头");Dog dog1 = new Dog("橘色",4);System.out.print(dog1.getAge() + "岁的" + dog1.getColor());dog1.lookHouse();Person person2 = new Person("老李",25);Cat cat = new Cat("灰色",3);person2.keepPet(cat,"小鱼干");cat.catchMouse();}
}

结果展示：