面向对象13：instanceof和类型转换

最新推荐文章于 2025-05-02 10:05:35 发布

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本文深入探讨Java中多态的概念，包括父类引用指向子类对象、向上转型与向下转型的具体操作，以及如何利用多态特性提高代码的灵活性和复用性。

package com.oop.demo06;

public class Application2 {
    public static void main(String[] args) {
//        Object --> String
//        Object --> Person --> Student
//        Object --> Person --> Teacher
        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);   编译不通过

        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);  编译不通过
//        System.out.println(person instanceof String);   编译不通过

        // 高转低需要强制转换   低转高不需要  低转高可能会损失方法
        Person person1 = new Student();
        person1.say();
        //分开写
        Student student2 = (Student) person1;
        student2.study();
        //合上写
        ((Student)person1).study();

        Student student1 = new Student();
        //分开写
        Person person2 = student1;
        person2.say();
//        person2.study();

        //合上写
        ((Student)person2).study();

    }
}

/*
1、父类引用指向子类的对象
2、把子类转成父类，向上转型；
3、把父类转成子类，向下转型； 需要强制转换
4、方便方法的调用，减少重复的代码

抽象： 封装、继承、多态！

 */