多态，instanceof

1.多态

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

public class Worker extends Person {
    @Override
    public void eat() {
        System.out.println("工人吃饭");
    }

    public void work(){
        System.out.println("工作");
    }
}

public class Student extends Person {
    @Override
    public void eat() {
        System.out.println("学生吃饭");
    }

    public  void study(){
        System.out.println("学习");
    }
}

public class Test02 {
    public static void main(String[] args) {
        //多态
        Person person = new Student();
        Person person1 = new Worker();

        person.eat();
        person1.eat();

        //强制类型转换
        Student student = (Student) person;
        student.study();
    }
}

2.instanceof：判断某个实例变量是否属于某种类的类型

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

public class Student extends Person {
    @Override
    public void eat() {
        System.out.println("学生吃饭");
    }

    public  void study(){
        System.out.println("学习");
    }
}

public class Worker extends Person {
    @Override
    public void eat() {
        System.out.println("工人吃饭");
    }

    public void work(){
        System.out.println("工作");
    }
}

public class Doctor {
    public void help(Person person) {
        person.eat();
        if (person instanceof Student) {
            Student student = (Student) person;
            student.study();
        } else if (person instanceof Worker) {
            Worker worker = (Worker) person;
            worker.work();
        }
    }
}

public class Test02 {
    public static void main(String[] args) {
        Student student = new Student();
        Worker worker = new Worker();
        Person person = new Person();

        Doctor doctor = new Doctor();
        doctor.help(student);
        doctor.help(worker);
        doctor.help(person);
    }
}