对象-多态

多态

课堂笔记

代码

package com.oop;

import com.oop.demo06.Person;
import com.oop.demo06.Student;

public class Application {
    public static void main(String[] args) {
        
        //一个对象的实际类型是确定的
        //new Student();
        //new Person();

        //可以指向的引用类型就不确定了：父类的引用指向了子类

        //能调用的方法都是自己的或继承父类的
        Student s1 = new Student();
        Person s2 = new Student();
        Object s3 = new Student();

        s2.run();//子类重写了父类的方法，执行子类的方法
        s1.run();
        
        //对象能执行哪些方法，主要看对象左边的类型，和右边关系不大
    }
}

Student类

package com.oop.demo06;

public class Student extends Person{
    
    public void run() {
        System.out.println("陈ying");
    }
}

Person类

package com.oop.demo06;

public class Person {
    public void run() {
        System.out.println("chenying");
    }
}

---

instance of类型转换

课堂截图

代码

package com.oop;

import com.oop.demo04.Teacher;
import com.oop.demo06.Person;
import com.oop.demo06.Student;

public class Application {
    public static void main(String[] args) {
        
        Object object = new Student();

        //System.out.println(X instanceof Y);// 能不能编译通过 ，取决于X和Y是否是父子关系或更远，但需为一条直线

        System.out.println(object instanceof Student); //true
        System.out.println(object instanceof Teacher);//false
        System.out.println(object instanceof Person);//true
        System.out.println(object instanceof Object);//true
        System.out.println(object instanceof String);//false
    }
}