将 ArrayList 对象添加到不同对象类型的现有 ArrayList

Question

Hopefully my title makes sense. What I am trying to do with my code is read a file line by line which has attributes about Students (Student ID, first name, last name, etc.) and the courses they've taken. I'm pretty confident my buffered reader is fine but I'm a little lost when it comes to the specifications of my program. The issue comes about when I am adding CourseList ArrayList objects to my Student ArrayList objects. The code runs fine, but does not add the courseLists to the student objects. Essentially I am making 2 Student ArrayLists that should have the courses stored in them relating to them. ie) Student1,Course1,Course2,etc..

Thank you in advance, here is my code:

import java.io.*;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.StringTokenizer;

public class studentDir {
    static int currentStudent = 0;
    public static void main(String args[]) throws IOException{
        ArrayList<Student> students = new ArrayList<Student>();

        Scanner input = new Scanner(new File("WarmUpData.txt"));

        while(input.hasNextLine()) {

            String line = input.nextLine();
            StringTokenizer st = new StringTokenizer(line,",");

                while(st.hasMoreTokens()){
                    String first, last, idNo;
                    last = st.nextToken();
                    first = st.nextToken();
                    System.out.println("Added student: "+last+", "+first);
                    idNo = st.nextToken();
                    System.out.println("Stored ID: "+idNo);
                    Student s = new Student(last, first, idNo);
                    students.add(s);
                    line = input.nextLine();
                    st = new StringTokenizer(line,",");
                    while(st.hasMoreTokens()){
                        String x = st.nextToken();
                        System.out.println("If controller read in: "+x);
                        if(x.equals("-999")){
                            line = input.nextLine();
                            st = new StringTokenizer(line, ",");
                            System.out.println("Added Credits & GPA");
                            Float totalCredits = Float.parseFloat(st.nextToken());
                            Float gpa = Float.parseFloat(st.nextToken());
                            students.get(currentStudent).storeGPA(totalCredits, gpa);
                            System.out.println("GPA Read In : "+students.get(currentStudent).getGPA());
                            currentStudent++;
                        }
                        else{
                            System.out.println("Adding course.");
                            String courseID = x;
                            float credits = Float.parseFloat(st.nextToken());
                            String grade = st.nextToken();
                            System.out.println(x+", "+grade);
                            CourseList cl = new CourseList(courseID,grade,credits);
                            s.add(cl);
                            System.out.println(cl.toString());
                            System.out.println(courseID+" "+credits+" "+grade+" added.");
                            line = input.nextLine();
                            st = new StringTokenizer(line,",");
                            }
                        }

                    for(Student x : students)
                        System.out.println(x.toString());                       
                }

        }
        input.close();      
        currentStudent = 0;
    }
}

import java.util.ArrayList;

public class Student {
    private String firstName;
    private String lastName;
    private String studentID;
    private float gpa;
    private float totalCredits;
    private ArrayList<CourseList> courses = new ArrayList<>();

    Student(String y, String x, String z){
            this.firstName = x;
            this.lastName = y;
            this.studentID = z;
    }

        public String toString(){
            String x = (this.firstName+" "+this.lastName+" "+this.studentID+".");
            return x;
        }
        public void setGPA(float x){
            this.gpa = x;
        }

        public float getGPA(){
            return gpa;
        }

        public String getID(){
            return this.studentID;
        }

        public void gpaCalc(Student stu, String id){
            totalCredits = 0;

        }

        public void storeGPA(float tcredits, float gpa){
            this.gpa = gpa;
            this.totalCredits = tcredits;
        }
        public void add(CourseList cl) {

        }

}

public class CourseList {
    String idNo, grade, courseID;
    float credits;
    float gpa;

    public CourseList(String x, String y, float z) {
        this.courseID = x;
        this.grade = y;
        this.credits = z;
    }

    public String toString(){
        String x = ("Course ID: "+this.courseID+", Grade : "+this.grade+", Credits Earned : "+this.credits+".");
        return x;
    }

    public float getCredits() {
        return this.credits;
    }
}


Input: 
Jones,Mary,903452
4342,2.5,A
3311,4,B+
-999
6.5,3.569
Martin,Joseph,312345
4598,3,C
1122,3,A-
2467,4,A
-999
10,3.31

Output: 
Added student: Jones, Mary
Stored ID: 903452
If controller read in: 4342
Adding course.
4342, A
Course ID: 4342, Grade : A, Credits Earned : 2.5.
4342 2.5 A added.
If controller read in: 3311
Adding course.
3311, B+
Course ID: 3311, Grade : B+, Credits Earned : 4.0.
3311 4.0 B+ added.
If controller read in: -999
Added Credits & GPA
GPA Read In : 3.569
Mary Jones 903452.
Added student: Martin, Joseph
Stored ID: 312345
If controller read in: 4598
Adding course.
4598, C
Course ID: 4598, Grade : C, Credits Earned : 3.0.
4598 3.0 C added.
If controller read in: 1122
Adding course.
1122, A-
Course ID: 1122, Grade : A-, Credits Earned : 3.0.
1122 3.0 A- added.
If controller read in: 2467
Adding course.
2467, A
Course ID: 2467, Grade : A, Credits Earned : 4.0.
2467 4.0 A added.
If controller read in: -999
Added Credits & GPA
GPA Read In : 3.31
Mary Jones 903452.
Joseph Martin 312345.

Thank you in advance guys!

Answer 1

IMHO, using ArrayList of two different types is not a good idea here. You should be using something like Map<Student, ArrayList<Course>> . It is:

1. Human readable and thus maintainable.
2. Its type safe.
3. Enables operations like searching for all courses taken by any student to complete in O(1).

Answer 2

In your code snipped your addCourse Method is empty

        public void add(CourseList cl) {

    }

I guess that is your problem here

Answer 3

Just set the ArrayList of CourseList to Student Class then it will work

public class studentDir {
                static int currentStudent = 0;
                public static void main(String args[]) throws IOException{
                    ArrayList<Student> students = new ArrayList<Student>();
    ArrayList<CourseList> courseLists=new ArrayList<>();
                    Scanner input = new Scanner(new File("WarmUpData.txt"));

                    while(input.hasNextLine()) {

                        String line = input.nextLine();
                        StringTokenizer st = new StringTokenizer(line,",");

                            while(st.hasMoreTokens()){
                                String first, last, idNo;
                                last = st.nextToken();
                                first = st.nextToken();
                                System.out.println("Added student: "+last+", "+first);
                                idNo = st.nextToken();
                                System.out.println("Stored ID: "+idNo);
                                Student s = new Student(last, first, idNo);

                                line = input.nextLine();
                                st = new StringTokenizer(line,",");
                                while(st.hasMoreTokens()){
                                    String x = st.nextToken();
                                    System.out.println("If controller read in: "+x);
                                    if(x.equals("-999")){
                                        line = input.nextLine();
                                        st = new StringTokenizer(line, ",");
                                        System.out.println("Added Credits & GPA");
                                        Float totalCredits = Float.parseFloat(st.nextToken());
                                        Float gpa = Float.parseFloat(st.nextToken());
                                        students.get(currentStudent).storeGPA(totalCredits, gpa);
                                        System.out.println("GPA Read In : "+students.get(currentStudent).getGPA());
                                        currentStudent++;
                                    }
                                    else{
                                        System.out.println("Adding course.");
                                        String courseID = x;

                                        float credits = Float.parseFloat(st.nextToken());
                                        String grade = st.nextToken();
                                        System.out.println(x+", "+grade);
                                        CourseList cl = new CourseList(courseID,grade,credits);
                                       courseLists.add(cl);
                                        s.setCourses(courseLists);
                                        System.out.println(cl.toString());
                                        System.out.println(courseID+" "+credits+" "+grade+" added.");
                                        line = input.nextLine();
                                        st = new StringTokenizer(line,",");

                                    }
                                    students.add(s);

                                    }

                                for(Student x : students)
                                    System.out.println(x);                       
                            }

                    }
                    input.close();      
                    currentStudent = 0;
                }
            }



     class Student {
        private String firstName;
        private String lastName;
        private String studentID;
        private float gpa;
        private float totalCredits;
        private ArrayList<CourseList> courses = new ArrayList<>();

        Student(String y, String x, String z) {
            this.firstName = x;
            this.lastName = y;
            this.studentID = z;
        }

        public String toString() {
            String x = (this.firstName + " " + this.lastName + " " + this.studentID + ".");
            return x;
        }

        public void setGPA(float x) {
            this.gpa = x;
        }

        public float getGPA() {
            return gpa;
        }

        public String getID() {
            return this.studentID;
        }

        public void gpaCalc(Student stu, String id) {
            totalCredits = 0;

        }

        public void storeGPA(float tcredits, float gpa) {
            this.gpa = gpa;
            this.totalCredits = tcredits;
        }



        public ArrayList<CourseList> getCourses() {
            return courses;
        }

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

    }

    class CourseList {
        String idNo, grade, courseID;
        float credits;
        float gpa;

        public CourseList(String x, String y, float z) {
            this.courseID = x;
            this.grade = y;
            this.credits = z;
        }

        public String toString() {
            String x = ("Course ID: " + this.courseID + ", Grade : " + this.grade + ", Credits Earned : " + this.credits
                    + ".");
            return x;
        }

        public float getCredits() {
            return this.credits;
        }
    }