Day8-3 instanceof和类型转换

instanceof和类型转换

判断一个对象是什么类型：instanceof

x instanceof y

 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 object = new Student();
         System.out.println(object instanceof Student);
         System.out.println(object instanceof Person);
         System.out.println(object instanceof Object);
         System.out.println(object instanceof Teacher);
     }
 }

类型转换

1. 父类引用指向子类对象

2. 把子类对象转换为父类，向上转型，自动转换

3. 把父类对象转换为子类，向下转型，强制转换

4. 方便方法调用，减少重复代码

 package com.oop.demo06;
 ​
 public class Person {
     public void run(){
         System.out.println("run");
     }
 }

 

 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) {
         //类型之间的转换
         //高                  低
         Person obj = new Student();
 ​
         //将student转换为Student类型，就可以使用Student类型的方法了
         ((Student)obj).go();
         //Student student = (Student)obj;
         //student.go();
         //子类转父类，可能会丢失自己本来的一些方法
         Student s1 =new Student();
         Person s2=s1;
 ​
     }
 }