code: @Override
      public void setRoundingMode(RoundingMode roundingMode) {
          if (roundingMode == null) {
              throw new NullPointerException();
          }
  
          this.roundingMode = roundingMode;
          digitList.setRoundingMode(roundingMode);
          fastPathCheckNeeded = true;
      }
docs: Sets the {@link java.math.RoundingMode} used in this DecimalFormat.
  
  @param roundingMode The <code>RoundingMode</code> to be used
  @see #getRoundingMode()
  @exception NullPointerException if <code>roundingMode</code> is null.
  @since 1.6