instanceof

• instanceof（类型转换）引用类型，判断一个对象是什么类型

package OOP.Demo09;

public class Application {
    public static void main(String[] args) {
        //Object > String
        //Object  > Person > Student
        //Object  > Person > Teacher
        //System.out.println(X instanceof Y);//能不能编译通过！通过：X和Y之间是否存在父子关系
        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
        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
    }
}

类型转换

• 父类引用指向子类的对象
• 把子类转换为父类，向上转型；
• 把父类转换为子类，向下转型——需要强制转换（可能会丢失一些方法）
• 方便方法的调用，减少重复的代码

万物皆有裂隙，那是光照进来的地方。