instanceof关键字实例与多态

实例代码如下：

Application类

package com.han.duotai;

/**
 * instanceof关键字实例，判断引用类型是否属于一个类型
 *
 * 关于多态
 * 1.父类的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，需要进行强制类型转换
 * 4.方便方法的调用，减少重复的代码
 */
public class Application {
    public static void main(String[] args) {
        Object obj = new Student();
        System.out.println(obj instanceof Person);//true
        System.out.println(obj instanceof Object);//true
        System.out.println(obj instanceof Student);//true
        System.out.println(obj instanceof Teacher);//false
        System.out.println(obj instanceof String);//false
        System.out.println("=======================================");
        Person person = new Student();
        System.out.println(person instanceof Person);//true
        System.out.println(person instanceof Object);//true
        System.out.println(person instanceof Student);//true
        System.out.println(person instanceof Teacher);//false
        //System.out.println(person instanceof String);//编译报错
        System.out.println("=======================================");
        Student student = new Student();
        System.out.println(student instanceof Person);//true
        System.out.println(student instanceof Object);//true
        System.out.println(student instanceof Student);//true
        //System.out.println(student instanceof Teacher);//编译报错
        //System.out.println(student instanceof String);//编译报错
        System.out.println("=======================================");
        Person person1 = new Student();
        ((Student) person1).go();//高转低-->强制类型转换
    }
}

Person类

package com.han.duotai;

public class Person {

}

Student类

package com.han.duotai;

public class Student extends Person{
    public void go(){

    }
}

Teacher类

package com.han.duotai;

public class Teacher extends Person{

}