instanceo

instanceo就是判斷前面是不是後面的型別

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，需要強制轉換，可能會丟失方法
4.方便方法的呼叫，減少重複的程式碼，簡潔
​
抽象: 封裝，繼承，多型！   抽象類:介面

package com.instanceo;
​
import com.duotai.Student;
​
public class Demo40 {
   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
​
     System.out.println(object instanceof Student);//ture
     System.out.println(object instanceof Person);//false
     System.out.println(object instanceof Object);//ture
     System.out.println(object instanceof Teacher);//false
     System.out.println(object instanceof String);//false
     System.out.println("===================================");
​
      Person person = new com.instanceo.Student();
     System.out.println(person instanceof com.instanceo.Student);//ture
     System.out.println(person instanceof Person);//true
     System.out.println(person instanceof Object);//ture
     System.out.println(person instanceof Teacher);//false
//     System.out.println(person instanceof String);//false
​
     System.out.println("===================================");
     com.instanceo.Student student = new com.instanceo.Student();
     System.out.println(student instanceof com.instanceo.Student);//ture
     System.out.println(student instanceof Person);//true
     System.out.println(student instanceof Object);//ture
//     System.out.println(student instanceof Teacher);//false
//     System.out.println(student instanceof String);//false
​
     //型別之間的轉換，基本型別轉換，高-低  父-子
     //父-子
     Person person1 = new com.instanceo.Student();
​
     //將person1這個物件轉換為Student型別，我們就可以使用student型別的方法了
     com.instanceo.Student student1 = (com.instanceo.Student)person1;
     student1.go();
​
     //子類轉換為父類;可能丟失自己的本來的一些方法
     com.instanceo.Student student2 = new com.instanceo.Student();
     student2.go();
     Person person2 = student2;
​
   }
}
/*
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，需要強制轉換，可能會丟失方法
4.方便方法的呼叫，減少重複的程式碼，簡潔
​
抽象: 封裝，繼承，多型！   抽象類:介面
​
 */
 

package com.instanceo;
​
public class Person {
   public void run(){
     System.out.println("run");
   }
}
​

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