instanceof和类型转换

1.Instanceof作用

    用来判断两个两个类之间是否存在父子关系 代码及详解如下： Application类代码

点击查看代码

package com.Tang.oop.demo06;

public class Application {
    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);编译就报错
        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
        /*
            总结：看编译能否通过主要是看对象左边的类型与instanceof 右边的类是否有父子关系
            看运行结果为true或false主要是看对象所指向的引用（右边的类）与instanceof右边的类是否存在父子关系
         */
    }
}

此时Student和Teacher类只是都继承了Person类所以并没有什么代码，就不在分别展示

2.强制转换

Application类代码

点击查看代码

package com.Tang.oop.demo06;

public class Application {
    public static void main(String[] args) {
        Person person = new Student();
        //Person相较于Student类是比较高的类，由高到低需要强制转换
        //也就是将person对象强制转化为Student类，才能调用go方法
        ((Student)person).go();
        Student student = new Student();
        student.go();
        //由低向高转则不需要强转，但是转化为高之后可能就会丢失一些方法
        Person person1 = student;
        // person1.go();
    }
}

Student类代码

点击查看代码

package com.Tang.oop.demo06;

public class Student extends Person{
    public void go(){
        System.out.println("go");
    }
}

Person类代码

点击查看代码

package com.Tang.oop.demo06;

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