一.多态
1.1 多态：一个事物的多种形态
1.2 多态的表现
行为(方法)多态：重写和重载。
引用多态(动态绑定):编译时的类型和运行时不一致的这种现象
例：父类 = 子类
Pet p = new Dog();
向上转型；父类=子类
例：Pet p = new Dog();
向下转型：子类 = （子类）父类
例: Dog d = (Dog)p;
public abstract class Pet {
private String name;
private int health=100;
private int age;
private int love=50;
public Pet(){
}
public Pet(String name,int health,int age,int love){
this.name = name;
this.health = health;
this.age = age;
this.love = love;
}
public String getName(){
return name;
}
public void setName(String name){
this.name= name;
}
public int getHealth(){
return health;
}
public void setHealth(int health){
this.health = health;
}
public int getAge(){
return age;
}
public void setAge(int age){
this.age = age;
}
public int getLove(){
return love;
}
public void setLove(int love){
this.love = love;
}
public void ji(){
System.out.println("宠物的自白：我的名字叫："+this.name+",年龄为："+this.age+"和主人的亲密度为："+this.love);
}
public abstract void eat();
}
宠物抽象类
public class Dog extends Pet{
private String strain;
public Dog(){
}
public Dog(String name,int health,int age,int love,String strain){
super(name,health,age,love);
this.strain = strain;
}
public void catchingFlyDisc(){
System.out.println("接飞盘");
int health = getHealth();
health = health-10;
setHealth(health);
int love = getLove();
love = love+5;
setLove(love);
}
public void eat(){
System.out.println("狗狗吃鱼");
}
public String getStrain(){
return strain;
}
public void setStrain(String strain){
this.strain = strain;
}
}
狗狗类继承宠物类
public class Penguin extends Pet {
private String sex;
public Penguin(){
}
public Penguin(String name,int health,int age,int love,String sex){
super(name,health,age,love);
this.sex = sex;
}
public void swimming(){
System.out.println("游泳");
int health = getHealth();
health = health-10;
setHealth(health);
int love = getLove();
love = love+5;
setLove(love);
}
public void eat(){
System.out.println("企鹅喝水");
}
public String getSex(){
return sex;
}
public void setSex(String sex){
this.sex = sex;
}
}
企鹅类继承宠物类
public class Master {
public void feed(Pet p){
p.eat();
}
public void play(Pet p){
if(p instanceof Dog ){
Dog d = (Dog) p;
d.catchingFlyDisc();
}else if(p instanceof Penguin){
Penguin pe = (Penguin) p;
pe.swimming();
}
}
}
主人类
public class TestPMPD {
public static void main(String[] args){
Master m= new Master();
//向下转型
Pet p = new Dog();
Dog d = (Dog) p;
m.feed(d);
// Pet p = new Penguin();
// m.feed(p);
}
}
测试类
运行结果为：
注意：java.lang.ClassCastException:类型转换异常
父类的运行时类型跟要转成的子类的类型不一致
注意：引用多态存在继承关系
二.instanceof
语法： 对象A instanceof 类型B
判断对象A的类型是否是类型B，是就返回true，否则返回false
例：d instanceof Dog
三.实现多态的2种形式
a.使用父类作为方法形参实现多态
public void play(Pet p){...}
b.使用父类作为方法返回值实现多态
public Pet getPet(int type){...}