code: public void prepare(StringDistance[] innerDistances) {
  		if (!fieldsPrepared) {
  			for (int i=0; i<size(); i++) {
  				StringDistance d = innerDistances[ getDistanceLearnerIndex(i) ];
  				set( i, d.prepare( get(i).unwrap() ) );
  			}
  		}
  	}
docs: Prepare each field with the appropriate distance