code: private int allocDataBlock() 
      {
          int newBlock = m_dataLength_;
          int newTop = newBlock + DATA_BLOCK_LENGTH;
          if (newTop > m_dataCapacity_) {
              // out of memory in the data array
              return -1;
          }
          m_dataLength_ = newTop;
          return newBlock;
      }
docs: private methods ------------------------------------------------------