java - Java关联数组列表

美好的一天，我与课程和学生有联系，该学生可以参加很多课程，并且一门课程有很多学生。学生班具有一个可比较的接口，该接口比较姓氏，因此在输出时，我可以使用collections.sort（）将名字排序为姓氏。因此，当我使用dirver类中的displayClassList（）方法将来自Courses类的学生放出时，输出不会显示任何内容。代码中缺少什么吗？

这些是类：

司机：

import java.util.*;
import java.beans.*;
import java.io.*;
import javax.swing.JOptionPane;
import java.beans.XMLDecoder;
import java.io.FileInputStream;
import java.util.*;
public class As3A_Driver
{
    public static void main(String[] args)
    throws IOException {
        // list of people
        Student harry = new Student("Harry", "Potter", 2, 3.65);
        Student ron = new Student("Ron", "Weasley", 2, 2.21);
        Student hermione = new Student("Hermione", "Granger", 2, 4.5);
        Student cho = new Student("Cho", "Chiang", 3, 4.05);
        Student ginny = new Student("Ginny", "Weasley", 1, 3.9);
        Instructor snape = new Instructor("Severus", "Snape", "M.Sc.");
        Instructor mcg = new Instructor("Minerva", "McGonigal", "Ph.D.");

        ArrayList<Person> people = new ArrayList<>();
        people.add(harry); people.add(ron); people.add(hermione);
        people.add(ginny); people.add(cho);

        // courses and associations
        Course course1 = new Course("WIZ-2666", "Potions II");
        Course course2 = new Course("WIZ-2989", "Transfiguration");
        course1.addInstructor(snape);
        harry.addCourse(course1);
        ron.addCourse(course1);
        hermione.addCourse(course1);
        cho.addCourse(course1);
        course2.addInstructor(mcg);
        harry.addCourse(course2);
        ron.addCourse(course2);
        hermione.addCourse(course2);
        ginny.addCourse(course2);

        // display class list
        course1.displayClassList();
        course2.displayClassList();


    }
}

培训班：

import java.util.*;
public class Course
{
    private String courseNumber;
    private String courseName;
    private ArrayList<Instructor> instructor;
    private ArrayList<Student> student;

    public Course(){
        courseNumber = courseName = "Unknown";
    }

    public Course (String courseName, String courseNumber){
        this.courseNumber=courseNumber;
        this.courseName=courseName;
        this.student=new ArrayList();
        this.instructor = new ArrayList();
    }

    public String getCourseNumber(){
        return courseNumber;
    }

    public String getCourseName(){
        return courseName;
    }

    public void setCourseNumber(){
        this.courseNumber=courseNumber;
    }

    public void setCourseName(){
        this.courseName=courseName;
    }

    public void setStudent(ArrayList<Student> student){
        this.student=student;
    }

    public ArrayList<Student> student(){
        return student;
    }

    public void addStudent(Student students){
        student.add(students);
    }

    public void addInstructor(Instructor i){
        instructor.add(i);
    }

    public void displayClassList(){
        System.out.println(getCourseName()+" "+ getCourseNumber());

        for(Instructor i: instructor){
            System.out.println("Instructor: "+i+", "+ i.getDegree());
        }

        System.out.println("Students:");

        for(Student s :student){
            Collections.sort(student);
            System.out.println(s.toString());
        }
    }
}

讲师：

import java.util.*;
public class Instructor extends Person
{
    private String degree;
    public ArrayList <Course> courses;
    public Instructor instructor;

    public Instructor(){
       firstName= lastName = degree= "unknown";
    }

    public Instructor (String F ,String L,String degree){
        super(F,L);
        this.degree=degree;
        this.courses=new ArrayList();
    }

    public void setCourses(ArrayList<Course> courses){
        this.courses=courses;
    }
    public ArrayList<Course> courses(){
        return courses;
    }

    public void addCourses (Course c){
        courses.add(c);
    }

    public String toString(){
        return lastName+","+firstName;
    }

    public String getDegree(){
        return degree;
    }
    public void setDegree(){
        this.degree=degree;
    }

}

人：

import java.util.*;
public abstract class Person
{
    protected String firstName;
    protected String lastName;

    public Person(){
        this.firstName=lastName = "Unknown";
    }

    public Person(String F ,String L){
        firstName=F;
        lastName=L;
    }

    public void setFirstName(){
        this.firstName=firstName;
    }
    public void setLastName(){
        this.lastName=lastName;
    }

    public String getFirstName(){
        return firstName;
    }
    public String getLastName(){
        return lastName;
    }

    public abstract String toString();

    public String getName(){
        return firstName+" "+lastName;
    }
}

学生：

import java.util.*;
public class Student extends Person  implements Comparable<Student>
{
    protected int year;
    protected double gpa;
    protected ArrayList<Course> course;

    public Student(){
        year = 0;
        gpa = 0.0;
        firstName= lastName= "unknown";
    }

    public Student(String F ,String L,int y, double g){
        super(F,L);
        this.year=y;
        this.gpa=g;
        course = new ArrayList();
    }

    public void setYear(){
        this.year=year;
    }

    public int getYear(){
        return year;
    }

    public void addCourse(Course c){
        course.add(c);
    }

    public void setCourses(ArrayList<Course> courses){
        this.course=courses;
    }

    public ArrayList<Course> course(){
        return course;
    }

    public void setGpa(){
        this.gpa=gpa;
    }

    public double getGpa(){
        return gpa;
    }

    public String getInfo(){
        return  getName()+" "+year+" "+gpa;
    }

    public String toString(){
        return lastName+","+firstName;
    }

    public int compareTo(Student lt){
       int lastName = this.lastName.compareTo(lt.lastName);
       return lastName == 0 ? this.firstName.compareTo(lt.firstName ): lastName;
    }
}

最佳答案

您可以尝试以下方法：

    // add students to courses
    course1.addStudent(harry);
    course1.addStudent(ron);
    course1.addStudent(hermione);
    course1.addStudent(cho);

    course2.addStudent(harry);
    course2.addStudent(ron);
    course2.addStudent(hermione);
    course2.addStudent(ginny);

    // display class list
    course1.displayClassList();
    course2.displayClassList();

输出：



注意：我已经将学生添加到课程中。除此之外，我还修改了displayClassList()方法，如下所示：

public void displayClassList(){
    System.out.println(getCourseName()+" "+ getCourseNumber());

    for(Instructor i: instructor){
        System.out.println("Instructor: "+i+", "+ i.getDegree());
    }

    System.out.println("Students:");

    Collections.sort(student);
    for(Student s :student){
        System.out.println(s.toString());
    }
}