新手学习Java之instanceof

instanceof

A(对象) instcnaceof B(类)结果为boolean型

A和B比较之前会先判断A能不能转换成B类型，能则通过，不能则编译报错

编译通过后会把A和B比较，如果A是B本类或者子类的对象，结果就是true，反之就是flase

如

先创建三个类，其中Person是Student和Teacher的父类
public class Person {
}

public class Student extends Person {
}

public class Teacher extends Person {
}

        //Object > Person > Student
        //Object > String
        //Object > Person > Teacher
以下是比较及结果：
            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 || object instanceof String中object是Object类型，String是Object的子类也继承了Object类型，所有能类型转换，编译通过
===============================================
        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);//编译报错！ || person instanceof String之所以编译会报错是因为person是Person类型，而String是final类型，两者不能转换
================================================
            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);//编译报错！
        //System.out.println(student instanceof String);//编译报错！