我写的关于继承的一个小练习，不清楚问什么出错，难道instanceof不该这么用吗？

[Euray_Kylin]

public class ExtendsDemo {
    public static void main(String[] args){
        Student s = new Student("张三",23);
        Teacher t = new Teacher("李四",35);
        Print(s);
        Print(t);
    }
    private static void Print(Person p){
        if(p instanceof Student){
            System.out.print(p.name+" "+p.age+" "+p.eat()+" ");
            p.learn();
        }
        else if(p instanceof Teacher){
            System.out.print(p.name+" "+p.age+" "+p.eat()+" ");
            p.teach();
        }
        else{ System.out.println("error");}
    }
}
class Person{
    public String name;
    public int age;
    public String eat(){
        return "吃饭";
    }
}
class Student extends Person{
    Student(String name,int age){
        this.name = name;
        this.age = age;
    }
    public void learn(){
        System.out.println("学习");
    }
}
class Teacher extends Person{
    Teacher(String name,int age){
        this.name = name;
        this.age = age;
    }
    public void teach(){
        System.out.println("教课");
    }
}

出错的提示


求教哪里用法不对啊

[Euray_Kylin]

[Jelly_Qin]

public class ExtendsDemo {
    public static void main(String[] args){
        Student s = new Student("张三",23);
        Teacher t = new Teacher("李四",35);
        Print(s);
        Print(t);
    }
    private static void Print(Person p){
        if(p instanceof Student){
            System.out.print(p.name+" "+p.age+" "+p.eat()+" ");
             Student student =(Student) p;
            student.learn();
        }
        else if(p instanceof Teacher){
            System.out.print(p.name+" "+p.age+" "+p.eat()+" ");
             Teacher teacher=(Teacher) p;
             teacher.teach();
        }
        else{ System.out.println("error");}
    }
}
class Person{
    public String name;
    public int age;
    public String eat(){
        return "吃饭";
    }
}
class Student extends Person{
    Student(String name,int age){
        this.name = name;
        this.age = age;
    }
    public void learn(){
        System.out.println("学习");
    }
}
class Teacher extends Person{
    Teacher(String name,int age){
        this.name = name;
        this.age = age;
    }
    public void teach(){
        System.out.println("教课");
    }
}

[wind_elf]

要向下转型把。（（Student）p）.learn(); （Teacher） p.teach();

[S117]

你父类中没有定义那么方法，当然访问不到了，把子类中的方法提到父类中去

[Jelly_Qin]

不过我不理解为什么不建立中间变量直接使用p=（Teacher）p和p=（Student）p不行

[qqZuok]

我记得好像父类不能转换成子类！

[bigdata-sb]

需要把p强制转换成Student或者Teacher类型啊

[郑涛]

用eclipse，保存直接编译，出错提示自己看，这个基本语法自己慢慢想吧

[白开水MD5]

引用 7 楼 qqZuok 的回复:

我记得好像父类不能转换成子类！

可以的，不过前提是这个父类是由子类转成的父类，比如他这个 Person(父类)是由Student和Teacher(子类)转的，所以可以转成父类

[Euray_Kylin]

忘记了强制转型，我已经懂了