HashSet with two equals object?

Question

I created an object HashSet, and the value is an object (Triple) which is my own class. But I get a strange thing, when there are two equal objects on my HashSet, is it possible? Here is my overriding method for the equals in the class Triple

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

 if(otherTriple.getSubject().equals(getSubject()) &&
   otherTriple.getPredicate().equals(getPredicate()) &&
   otherTriple.getObject().equals(getObject()))
  return true;
 return false;

}

Answer 1

You need to be sure to implement hashCode() as well, and when two Triples are equal, their hashCodes must also be equal. If you don't do that, you will get strange behavior.