Java:多态 之 向上转型

知识总结：

父类：

Animal.java:

package com.imooc.animal;

public class Animal {
private String name;
private int month;

public Animal(){

}

public Animal(String name,int month){
this.setName(name);
this.setMonth(month);
}

//eat()
public void eat(){
System.out.println("动物都又吃东西的能力！");
}

//getter/setter
public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getMonth() {
return month;
}

public void setMonth(int month) {
this.month = month;
}

}

Cat.java:

package com.imooc.animal;

public class Cat extends Animal {

private String name;
private int month;
private double weight;

public Cat(){

}

public Cat(String name,int month,double weight){
super(name,month);//super父类属性构造方法赋值
setWeight(weight);
}

//run
public void run(){
System.out.println("猫会跑");
}

//方法重写
@Override
public void eat() {
System.out.println("猫吃鱼！");
}

//getter/setter
public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getMonth() {
return month;
}

public void setMonth(int month) {
this.month = month;
}

public double getWeight() {
return weight;
}

public void setWeight(double weight) {
this.weight = weight;
}

}

Dog.java:

package com.imooc.animal;

public class Dog extends Animal {
private String name;
private int month;
private String sex;

public Dog(){

}

public Dog(String name,int month,String sex){
super(name,month);
this.setSex(sex);
}

//sleep
public void sleep(){
System.out.println("小狗会午睡");
}

//方法重写
@Override
public void eat() {
System.out.println("狗吃肉！");
}

//getter/setter
public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getMonth() {
return month;
}

public void setMonth(int month) {
this.month = month;
}

public String getSex() {
return sex;
}

public void setSex(String sex) {
this.sex = sex;
}

}

test.java:

package com.imooc.test;

import com.imooc.animal.Animal;
import com.imooc.animal.Cat;
import com.imooc.animal.Dog;

public class test {

public static void main(String[] args) {
Animal one=new Animal();//1

/* * 向上转型（隐式转型），自动转型 * 父类引用指向子类的实例，可以调用子类重写父类的方法以及父类的派生方法，但是该对象无法调用子类独有的方法 * 注意：父类中的静态方法无法被子类重写，所以向上转型之后，只能调用父类原油的的静态方法 * 小类转大类 */

Animal two=new Cat();//2
Animal three=new Dog();//3

one.eat();
two.eat();
three.eat();

two.setMonth(3);
two.getMonth();
three.setName("花花");
three.getName();

//two.run();编译错误
//three.sleep();编译报错

}

}

向上转型也可以写成：



执行情况：