set - Issue with "contains" hashset method (Java) -

the following code not giving me result i'm expecting:

public static void main (string[] args) {      set<pair> objpair = new linkedhashset<pair>();     objpair.add(new pair(1, 0));      system.out.println("does pair (1, 0) exists already? "+objpair.contains(new pair(1, 0)));  }  private static class pair {      private int source;     private int target;      public pair(int source, int target) {       this.source = source;       this.target = target;     }         } 

the result be:

does pair (1, 0) exists already? false 

i can't understand why it's not working. or maybe i'm using "contains" method wrong (or wrong reasons).

there issue, if add same value twice, accepted, being set

objpair.add(new pair(1, 0)); objpair.add(new pair(1, 0)); 

it won't accept/recognize class pair i've created?

thanks in advance.

without own hashcode() implementation, java considers 2 pair objects equal if exact same object , new, definition, creates 'new' object. in case, want pair objects consider equal if have same values source , target -- this, need tell java how should test pair objects equality. (and make hash maps work way expect, need generate hash code consistent equals -- loosely speaking, means equal objects must generate same hashcode, , unequal objects should generate different hash codes.

most ides generate decent hashcode() , equals() methods you. mine generated this:

  @override    public int hashcode() {       int hash = 3;       hash = 47 * hash + this.source;       hash = 47 * hash + this.target;       return hash;    }     @override    public boolean equals(object obj) {       if (obj == null) {          return false;       }       if (getclass() != obj.getclass()) {          return false;       }       final pair other = (pair) obj;       if (this.source != other.source) {          return false;       }       if (this.target != other.target) {          return false;       }       return true;    }