public long get(int idx) {
    Preconditions.checkElementIndex(idx, this.values.size());
    return this.values.get(idx);
  }
public long get ( int idx ) { Preconditions . checkElementIndex ( idx , this . values . size ( ) ) ; return this . values . get ( idx ) ; }
The idx'th value of this watermark. idx must be between 0 and size()-1.
@return