instanceof关键字 2021-06-12

Posted 2021-07-14 超霸霸

• instanceof关键字用来对比左边的对象是否属于右边的对象

实例演练

• 定义一个Person父类和Student子类和Teacher子类

Object object=new Student();
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

运行结果为：

true
true
true
false
false

Person person=new Student();
System.out.println(person instanceof Student);//true
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);  编译报错

运行结果为：

true
true
true    
false     

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);  编译报错
//System.out.println(student instanceof String);  编译报错

运行结果为：

true
true    
true    

---

总结

1. 父类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：强制转换
4. 方便方法的调用，减少重复的代码