instanceof關鍵字例項與多型

例項程式碼如下：

Application類

package com.han.duotai;

/**
 * instanceof關鍵字例項，判斷引用型別是否屬於一個型別
 *
 * 關於多型
 * 1.父類的引用指向子類的物件
 * 2.把子類轉換為父類，向上轉型
 * 3.把父類轉換為子類，向下轉型，需要進行強制型別轉換
 * 4.方便方法的呼叫，減少重複的程式碼
 */
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);//編譯報錯
        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);//編譯報錯
        //System.out.println(student instanceof String);//編譯報錯
        System.out.println("=======================================");
        Person person1 = new Student();
        ((Student) person1).go();//高轉低-->強制型別轉換
    }
}
 

Person類

package com.han.duotai;

public class Person {

}

Student類

package com.han.duotai;

public class Student extends Person{
    public void go(){

    }
}

Teacher類

package com.han.duotai;

public class Teacher extends Person{

}