code: public void copy(int srcIdx, byte[] dst, int dstIdx, int length) {
          if (isOutOfBounds(srcIdx, length, length())) {
              throw new IndexOutOfBoundsException("expected: " + "0 <= srcIdx(" + srcIdx + ") <= srcIdx + length("
                              + length + ") <= srcLen(" + length() + ')');
          }
  
          System.arraycopy(value, srcIdx + offset, checkNotNull(dst, "dst"), dstIdx, length);
      }
docs: Copies the content of this string to a byte array.
  
  @param srcIdx the starting offset of characters to copy.
  @param dst the destination byte array.
  @param dstIdx the starting offset in the destination byte array.
  @param length the number of characters to copy.