instanceof 类型转换-蒲公英云

instanceof 类型转换

叁歲伎倆 2024-03-27 15:09 128阅读 0赞

instanceof （类型转换）引用类型判断一个对象是什么类型

1. 父类引用指向子类对象
2. 把子类转化为父类，向上转型；
3. 把父类转化为子类，向下转型，强制转换
4. 方便方法的调用，减少重复的代码！简洁
public class Application {
    public static void main(String[] args) {
        //Object-->String
        //Object-->Person-->Teacher
        //Object-->Person-->Student
        Object object = new Student();
        //System.out.println(x instanceof y);//会不会编译报错！要看有没有关系
        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);//编译报错！
        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);//编译报错！
        //System.out.println(student instanceof String);//编译报错！
    }
}
package com.oop;
import com.oop.demo06.Person;
import com.oop.demo06.Student;
public class Application {
    public static void main(String[] args) {
    //类型之间的转化：父     子
        //高                 低
        Person obj = new Student();
        //obj 将这个对象转化为Student类型，这样我们就能使用Student类型的方法了
       /* Student student = (Student) obj;
        student.go();*/
        ((Student)obj).go();
        //子类转化为父类，可能丢失自己本来的一些方法
        Student student = new Student();
        Person person = student;
    }
    /*
    1. 父类引用指向子类对象
    2. 把子类转化为父类，向上转型；
    3. 把父类转化为子类，向下转型，强制转换
    4.方便方法的调用，减少重复的代码！简洁
     */
}
package com.oop.demo06;
public class Student extends Person{
    public void go(){
        System.out.println("go");
    }
}
package com.oop.demo06;
public class Person {
    public void run() {
        System.out.println("run");
    }
}