title: Add optional params to methods in a trait scala
body: <p>I have a trait with a method that's being used by 3 different classes, in one of the classes, I would like to override the method to accept an additional param, is this possible? how would one go about this in scala?</p>
  <p>PS: I am new to Scala</p>
  <p>Desired example:</p>
  <pre><code>trait Iterator {
      def hasNext(a : String): 
  }
  class Iterator extends Iterator {
     override def hasNext(a : String, b: String) = {
       ...
     }
  }
  </code></pre>