Java面向对象系列（11）- instanceof和类型转换

instanceof

先看引用类型的类和instanceof比较的类有没有父子关系，有则可以编译，IDEA不报错
new一个对象，对象new所在的类和instanceof比较的类有没有父子关系，有则为True，无则为Fals
即编译看左边，运行结果True还是False看右边

例子关系

//Object > String
//Object > Person > Teacher
//Object > Person > Student

场景一

package demo01;

public class Application {
    public static void main(String[] args) {
        //Object > String
        //Object > Person > Teacher
        //Object > Person > Student
        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


    }
}

场景二

        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);//编译就报错了

场景三

        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);//编译就报错了
        System.out.println(student instanceof  String);//编译就报错了