How to store unique pair of strings in Java?

Question

I have written a simple test program in which I am trying to store unique pair of (String,String). Here below I mentioned my code part:

 public class Pair {
        private String cr_ts_hi;
        private String cr_ts_lo;

        //constructor and getter-setter
 }

 class Test{

     private static HashSet<Pair> caseExceptionReport = new LinkedHashSet<Pair>();

     public static void main(String[] args) {
        caseExceptionReport.add(new Pair("abc","itm1"));caseExceptionReport.add(new Pair("abc","itm2"));
        caseExceptionReport.add(new Pair("abc","itm1"));caseExceptionReport.add(new Pair("def","itm1"));
        caseExceptionReport.add(new Pair("def","itm2"));caseExceptionReport.add(new Pair("def","itm2"));
        caseExceptionReport.add(new Pair("xyz","itm1"));caseExceptionReport.add(new Pair("xyz","itm2"));

        for(Pair m:caseExceptionReport){
            System.out.println(m.getCr_ts_hi() + "   ***   " + m.getCr_ts_lo());
        }
 }

And output is:

  abc *** item1
  abc *** item2
  abc *** item1
  def *** item1
  def *** item2
  def *** item2
  xyz *** item1
  xyz *** item2

Expected output is:

 abc *** item1
 abc *** item2
 def *** item1
 def *** item2
 xyz *** item1
 xyz *** item2

I am not getting a way to store unique pairs. I though HashSet won't allow duplicate Pair's but it is not working. Any other idea for this?

override equals and hashcode method in Pair class – Balaji Krishnan Feb 12 '16 at 06:51 — Balaji Krishnan, Feb 12 '16 at 06:51

wX2qJ2hUdVhnMtWE · Answer 1 · 2016-02-12T07:29:17.443

1

You need to override hashCode() and equals() otherwise you're defaulting to Object's implementation.

See: docs.

edited Feb 12 '16 at 07:29

answered Feb 12 '16 at 06:55

wX2qJ2hUdVhnMtWE

46
6

score 1 · Answer 2 · edited May 23 '17 at 11:59

1

You need to override the equals() and hashCode() methods in your Pair class. Please follow the below related link for details:

HashSet does not seem to realize that two objects are the same

edited May 23 '17 at 11:59

Community

1
1

answered Feb 12 '16 at 06:55

niraj

17,498
4
33
48

score 1 · Accepted Answer · answered Feb 12 '16 at 07:34

You need to define the equality of the Pair

public class Pair {
    private String cr_ts_hi;
    private String cr_ts_lo;

    //constructor and getter-setter

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Pair pair = (Pair) o;

        if (cr_ts_hi != null ? !cr_ts_hi.equals(pair.cr_ts_hi) : pair.cr_ts_hi != null) return false;
        return cr_ts_lo != null ? cr_ts_lo.equals(pair.cr_ts_lo) : pair.cr_ts_lo == null;
    }

    @Override
    public int hashCode() {
        int result = cr_ts_hi != null ? cr_ts_hi.hashCode() : 0;
        result = 31 * result + (cr_ts_lo != null ? cr_ts_lo.hashCode() : 0);
        return result;
    }
}

Thanks for the solution :) – Madhusudan Feb 16 '16 at 04:22 — Madhusudan, Feb 16 '16 at 04:22

How to store unique pair of strings in Java?

3 Answers3