public String toString(){
  StringBuffer sb=new StringBuffer();
  for (  Pair next : mapping) {
    sb.append(next.getKey() + ':' + next.getValue()+ ',');
  }
  return sb.toString();
}

public String toString ( ) { StringBuffer sb = new StringBuffer ( ) ; for ( Pair next : mapping ) { sb . append ( next . getKey ( ) + ':' + next . getValue ( ) + ',' ) ; } return sb . toString ( ) ; }
return the list of values as a single string separated by a colon , comma
