Calculate Audio Level

How to calculate audio level from PCM sample data:

http://en.wikipedia.org/wiki/Root_mean_square
Sample Code

  protected void updateLevelAndPeak(ByteBuffer bytebuffer, int bufferLen) {
    int numFrame = bufferLen / frameSizeInBytes;
    long sampleSqureTotal = 0L;
    long peak = 0L;
    ShortBuffer shortbuffer = bytebuffer.asShortBuffer();
    for (int indexFrame = 0; indexFrame < numFrame; indexFrame++) {
      int sampleValue = 0;
      for (int indexChannel = 0; indexChannel < channels; indexChannel++) {
        sampleValue += shortbuffer.get(channels * indexFrame + indexChannel);
      }

      sampleValue /= channels;
      int k = Math.abs(sampleValue);
      sampleSqureTotal += sampleValue * sampleValue;
      if ((long) k > peak) {
        peak = k;
      }
    }

    currentLevel = numFrame <= 0 ? 0.0D : Math.sqrt(sampleSqureTotal / (long) numFrame);
    currentPeak = peak;
  }

Reference:
http://wiki.hydrogenaudio.org/index.php?title=Replaygain