instanceof 类型转换

叁歲伎倆 2024-03-27 15:09 66阅读 0赞

### instanceof （类型转换）引用类型 判断一个对象是什么类型 ###

1. 父类引用指向子类对象
    2. 把子类转化为父类，向上转型；
    3. 把父类转化为子类，向下转型，强制转换
    4. 方便方法的调用，减少重复的代码！简洁

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);//会不会编译报错！要看有没有关系
    
            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 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！
    
            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);//编译报错！
            //System.out.println(student instanceof String);//编译报错！
    
        }
    }

package com.oop;
    
    import com.oop.demo06.Person;
    import com.oop.demo06.Student;
    
    public class Application {
        
        public static void main(String[] args) {
        
        //类型之间的转化：父     子
            //高                 低
            Person obj = new Student();
    
            //obj 将这个对象转化为Student类型，这样我们就能使用Student类型的方法了
           /* Student student = (Student) obj;
            student.go();*/
            ((Student)obj).go();
    
            //子类转化为父类，可能丢失自己本来的一些方法
            Student student = new Student();
            Person person = student;
        }
        /*
        1. 父类引用指向子类对象
        2. 把子类转化为父类，向上转型；
        3. 把父类转化为子类，向下转型，强制转换
        4.方便方法的调用，减少重复的代码！简洁
         */
    }

package com.oop.demo06;
    
    public class Student extends Person{
        
    
        public void go(){
        
            System.out.println("go");
        }
    }

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