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

I am having trouble understanding your question but hashCode() and equals() sematics are important only when you are planning to use an object as the key. And you cant have two objects evaluating to same hash in a Map...one will override the other

Answer 2

You didn't override equals and hashCode in your class properly. Here's how to write it and test it :

http://java.sun.com/developer/Books/effectivejava/Chapter3.pdf

Answer 3

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.