Getting values from one Array List using objects of another array list java

Question

I have 3 ArrayLists.

Students (ID, Name, Program)
Courses (ID, Name, Credit Hours)
StudentCourses (StudentId, CourseID)

I am searching from StudentCourses by passing the StudentID and getting the courses registered with his/her name. My StudentCourse ArrayLIst has objects like this

49 (Student ID) CS233(Course ID)

49 (Student ID) CS231(Course ID)

When a user searches for a student, say I'm searching for Johnna with her registration number 49. The result is

Reg ID: 49 Name : Johnna Program: BSCS Courses Registered: CS233 CS231

Which is fine. But, what I really need to do is get the name of the course using the course IDs that appear in the search info of Johnna. The Course ArrayList looks like this:

CS233 OOP BSCS

CS231 ALgorithms BSCS

I tried this code but it didn't seem to work. It keeps giving either garbage values or it just prints all Course names until there is a null exception:

if (myStudent == null) {
    System.out.print("No Record Was Found");
} else {
    System.out.print("Student ID: " + myStudent.getID() + "\nFull Name: " + myStudent.getName() + "\nProgram: " + myStudent.getProgram() +

    "\nTotal Credit Hours: " + (Integer.parseInt(myStudent.getTotalCreds())) * 3420 + "Rs" + "\nCourses Registered:\n");
}
for (int i = 0; i < studCourseList.size(); i++) {
    if (studCourseList.get(i).getSid().equals(ID)) {

        System.out.print("- " + studCourseList.get(i).getCid() + "\n");
        for (int j = 0; j < CoursesList.size(); j++) {
        if(CoursesList.get(i).getID().equals(studCourseList.get(i).getCid())){
                System.out.print("- " + CoursesList.get(i).getName() + "\n");
                break;
            }

        }

    }

}

The upper portion is bringing the Student info, the first loop is for the Courses registered against the student ID, and the second loop is not working. Note that all objects are on different lines.

Tyler Gaona · Accepted Answer · 2014-04-13 16:50:37Z

1

Well for starters, remove the semicolon after this if statement! if(CoursesList.get(i).getID().equals(studCourseList.get(i).getCid()))

If that doesn't solve your problem, we're going to need more information about what studCourseList and CoursesList is. My inclination would be to guess that in your second loop you should use j like so: if (CoursesList.get(j).getID().equals(studCourseList.get(i).getCid()))

But without explicit knowledge of your classes I can't be sure if that is correct.

answered Apr 13, 2014 at 16:50

Tyler Gaona

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1 Comment

Tyler Gaona Over a year ago

I'm glad it helped. Please don't forget to accept an answer to close the question.

yitzih · Accepted Answer · 2014-04-13 16:50:02Z

1

In your nested for loop you use 'j' as a counter but inside that loop you reference 'i'.

for (int j = 0;j<CoursesList.size(); j++){
    if (CoursesList.get(i).getID().equals(studCourseList.get(i).getCid()));
    {
        System.out.print("- " + CoursesList.get(i).getName() + "\n");
        break;
    }

It looks like

.equals(studCourseList.get(i).getCid()

should use 'j' as a reference otherwise you are not actually going through the studCourseList and are just comparing the same two items over and over.

answered Apr 13, 2014 at 16:50

yitzih

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1 Comment

momal Over a year ago

Oh yeah I realized this too. Changed it and removed the semi colon from the if statement

Braj · Accepted Answer · 2014-04-13 16:52:58Z

1

I suggest you to use Map in place of List in this situation where Id is treated as key and POJO as its value.

HashMap is more faster than List in search.

Sample code:

class Student {
    private String id;
    private String name;
    private String program;
    // getter setter
}

class Course {
    private String id;
    private String name;
    private int creditHours;
    // getter setter
}

class StudentCourses {
    private String studentId;
    private String courseId;
    // getter setter
}

Map<String, Student> students = new HashMap<String, Student>();
Map<String, Course> courses = new HashMap<String, Course>();

edited Apr 13, 2014 at 16:52

answered Apr 13, 2014 at 16:46

Braj

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3 Comments

momal Over a year ago

My whole project is based on ArrayLists. I've never used Map before.

Braj Over a year ago

No issue. Its not too late. Just use it for good performance. If possible :)

momal Over a year ago

I have to submit it tomorrow, otherwise i would have used it :) I hope this answer helps other newbies like me

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