Person类：

public class Person {
    public void go(){
        System.out.println("go");
    }
}

Teacher类继承Person类：

public class Teacher extends Person {
}

Student类继承Person类：

public class Student extends Person {
}

主函数：

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

运行结果：

主函数：

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

运行结果：

主函数：

Student student = new Student();
System.out.println(student instanceof Student);
System.out.println(student instanceof Person);
System.out.println(student instanceof Object);
//System.out.println(student instanceof Teacher);//编译报错
//System.out.println(person instanceof String);//编译报错

运行结果：

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

instanceof用来判断两个类型之间是否存在父子关系
父转子需强制转换，子转父可能会丢失方法