instanceof与类型转换

instanceof与类型转换

package com.andy.base.oop.demo01.demo06;

public class Teacher extends Person {

}

package com.andy.base.oop.demo01.demo06;

public class Student extends Person {

    public  void go(){
        System.out.println("go");
    }

}

/*
   //Object > String
        //Object > Person >Teacher
        //Object > Person >Student
        Object object = new Student();

        System.out.println(object instanceof Student);//true
        System.out.println(object instanceof Person);//true
        System.out.println(object instanceof Object);//true
        System.out.println(object instanceof Teacher);//false
        System.out.println(object instanceof String);//false
        System.out.println("==============================");
        Person person = new Student();
        System.out.println(person instanceof Student);//true
        System.out.println(person instanceof Person);//true
        System.out.println(person instanceof Object);//true
        System.out.println(person instanceof Teacher);//false
        //System.out.println(person instanceof String);// 编译错误
        System.out.println("==============================");
        Student student = new Student();
        System.out.println(student instanceof Student);//true
        System.out.println(student instanceof Person);//true
        System.out.println(student instanceof Object);//true
        //System.out.println(student instanceof Teacher);// 编译错误
        //System.out.println(person instanceof String);// 编译错误
 */

package com.andy.base.oop.demo01.demo06;

public class Person {

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

}

main

package com.andy.base.oop.demo01;

import com.andy.base.oop.demo01.demo06.Person;
import com.andy.base.oop.demo01.demo06.Student;

public class Application {
    public static void main(String[] args) {

        //基本类型转换： 父（高）   子（低）

        //高                    低
        Person student = new Student();
       // student.go();    //student调用的是 Person ，Person类中没有go方法

        //student 将这个对象转换为Student类型，我们就可以使用Student类型的方法了！
        ((Student)student).go();

        Student student1 = new Student();
        student1.go();
        Person person = student;    //低 --->高 （自动）Student --->Person

    }
}

/*
1.父类引用指向子类的对象
2.把子类转换为父类，向上转型；
3.把父类转换为子类，向下转型；强制转换
4.放便方法的调用，减少重复的代码！简介

封装、继承 、多态    抽象类，接口
 */