Day15

package com.oop.demo06;

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

package com.oop.demo06;

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


/*
package com.oop;

        import com.oop.demo06.Person;
        import com.oop.demo06.Student;
        import com.oop.demo06.Teacher;

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);能不能編譯通過！就是看x和y之間是否存在父子關係


        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 Person();
        System.out.println(person instanceof Student);//flase
        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);//編譯報錯
        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);//編譯報錯
        //System.out.println(student instanceof String);//編譯報錯
    }
}
 */









/*
多態註意事項：
1、多態是方法的多態，屬性沒有多態
2、父類和子類有聯繫   類型轉換異常（ClassCastException）
3、存在條件：繼承關係，方法需要重寫，父類引用指向子類對象 Father f1=new son();


不能重寫，也沒有多態的方法
1、static 方法，屬於類，它不屬於示例
2、final 常量
3、private方法
 */

package com.oop.demo06;

public class Teacher extends  Person{
}

package com.oop;

import com.oop.demo06.Person;
import com.oop.demo06.Student;
import com.oop.demo06.Teacher;

public class Application {
    public static void main(String[] args) {
        //類型直接的轉換：基本類型轉換 父  子
        //高                低
        Person s1=new Student();
        //student這個對象轉換成Student類型,我們就可以使用Student類型的方法
       Student student= (Student)s1;//高轉低強制轉換
        //子類轉換成父類可能會丟失一些方法
        Student s2=new Student();
        s2.go();
        Person person=student;
    }
}
/*
1、父類引用指向子類對象
2、把子類轉換成父類，向上轉型
3、把父類轉換成子類，向下轉型，需強制轉換
4、方便方法的調用，減少重覆的代碼
 */