public void addOption(T option,double weight){
  if (weight < 0)   throw new IllegalArgumentException("Negative weight not allowed.");
  options.add(option);
  weights.add(weight);
  weightSum+=weight;
}

public void addOption ( T option , double weight ) { if ( weight < 0 ) throw new IllegalArgumentException ( "Negative weight not allowed." ) ; options . add ( option ) ; weights . add ( weight ) ; weightSum += weight ; }
adds an option to the choice set .
