title: java collection of unique elements
body: <p>I have a Collection coll of myObject. I'd like to add an element to coll only if there is no such element in the collection.</p>
  
  <p>I have overriden the equals method of myObject. It checks for the equality of its 20 attributes.</p>
  
  <p>However in the case of the collection, I'd like to make the equality check (and hence the add) based only on one of these attributes.</p>
  
  <p>Maybe my architecture is flawed, and I shouldn't have two definitions of equals, and should instead have 2 different objects.</p>
  
  <p>However, is it possible, without too much refactoring, to achieve what I want from here ? That is to say, I'd like some sort of a Set collection, where I could tell how to make the comparison check. This would be similar to the Collection.sort() method, where you can provide the comparator to check for the comparison.</p>