如何使用泛型限制子类中的方法参数类型？

Question

我有一个名为Teacher 的父类定义如下：

import java.util.LinkedList;
import java.util.List;

public class Teacher {
    public List<Student> list = null;

    public Teacher(String id) {
        list = new LinkedList<Student>();
    }

    public void addStudent(Student tb){
        list.add(tb);
    }
}

和Student:

public class Student {
    public String getStudentName(){
        return "student";
    }
}

还有一个扩展Teacher的子类和一个扩展Student的子类：

import java.util.List;

public class MathStudent extends Student{
    public String getStudentName(){
        return "math student";
    }
}

public class MathTeacher extends Teacher{

    public MathTeacher(String id) {
        super(id);
        // TODO Auto-generated constructor stub
    }
}

显然，MathTeacher 继承了方法addStudent。 但问题是，当我构造一个MathTeacher 对象并为其添加一个学生时，我只希望它是MathStudent 而不是Student，如下所示：

MathTeacher clc = new MathTeacher("a");
MathStudent tc = new MathStudent();
clc.add(tc);
Student student = new Student();
clc.add(student); // I want this line to throw compling error to avoid a Student object is added

我能做什么？我猜java泛型可能有用。

Answer 1

您可以通过以下方式实现它：

public class Teacher <T extends Student> {
    public List<T> list = null;

    public Teacher(String id) {
        list = new LinkedList<T>();
    }

    public void addStudent(T tb){
        list.add(tb);
    }
}

public class MathTeacher extends Teacher <MathStudent> {

    public MathTeacher(String id) {
        super(id);
        // TODO Auto-generated constructor stub
    }
}