instanceof关键字实例与多态

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{

}