Which collection should be used in this scenario?

Question

Can any one suggest me which collection to use for this scenario:

Every student has a payment history with details of payment made by the student / family. The system should ensure that no duplicate payments are there against a student account. The program should be able to add payment details for a student, and ensure that duplicate payment details are not getting registered.

I don't think the collection type is going to matter. I think you should perform the duplicate check against the collection yourself rather than relying on the collection to do it. — Rup, Sep 05 '11 at 19:16

score 6 · Accepted Answer · answered Sep 05 '11 at 19:16

6

Perhaps a Map<Student, Set<Payment>> would do.

(A Set won't allow for duplicates.)

If you override equals properly (and hashCode) you can do something like

Map<Student, Set<Payment>> studentPayments =new HashMap<Student, Set<Payment>>();

public void addStudentPayment(Student student, Payment payment) {

    if (!studentPayments.containsKey(student))
        studentPayments.put(student, new HashSet<Payment>());

    if (studentPayments.get(student).add(payment))
        System.out.println("Payment was added");
    else
        System.out.println("Duplicate found. Payment not added.");
}

answered Sep 05 '11 at 19:16

aioobe

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that requires me to see the rest of your person / payment clasess. Besides, I think you should post a new question for that, giving the details. If you post a link to the question here, I'll have a look at it. – aioobe Sep 05 '11 at 19:27
its just a employment program where there will be savings account and related account for that in the name of a student.And based on his saving every month there will be a credit of 75% in related employment program account. – satheesh Sep 05 '11 at 19:32
I think the best advice I can give you is to have a look at [this](http://stackoverflow.com/questions/27581/overriding-equals-and-hashcode-in-java) question, and post a more specific follow-up question if that doesn't provide enough info. – aioobe Sep 05 '11 at 19:42
ok Mr aioobe i will try working on that ..if i have anything to clarify i will post ... – satheesh Sep 05 '11 at 19:46

score 3 · Answer 2 · answered Sep 05 '11 at 19:15

3

whenever you have a requirement for no duplicates, Use a Set. If you use a HashSet, make sure to implement hashCode on the Objects you put in the set (and also equals).

answered Sep 05 '11 at 19:15

hvgotcodes

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score 1 · Answer 3 · edited Sep 05 '11 at 19:23

1

You might find a Map of students to a set of payments helpful

Map<Student, Set<Payment>> studenthistory;

edited Sep 05 '11 at 19:23

aioobe

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answered Sep 05 '11 at 19:17

Jonathan Weatherhead

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Jiri Kriz · Answer 4 · 2011-09-05T19:30:31.600

1

You can consider e.g.

Map<Student, HashSet<Payment>> students;

Student is the student, identified by name or some ID. HashSet<Payment> are the payments. A Payment contains an ID, amount, date, etc.

edited Sep 05 '11 at 19:30

answered Sep 05 '11 at 19:19

Jiri Kriz

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Surely two payments can be of the same amount. Besides, `Double` is a terrible type for storing currency. – aioobe Sep 05 '11 at 19:24
@aioobe: Agree. Improved now. – Jiri Kriz Sep 05 '11 at 19:31

score 0 · Answer 5 · edited Sep 05 '11 at 19:27

A set would be your best choice. A set is a collection that contains no duplicate elements.

Just remember to override the equals-method on your class: http://www.javapractices.com/topic/TopicAction.do?Id=17

In your case, it will be something like:

public boolean equals(Object obj) {
    if (!obj instanceof Payment)
        return false;
    }
    Payment p = (Payment) o;
    return p.getId().equals(getId());
}

.... or something like that :)

Which collection should be used in this scenario?

5 Answers5

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