code: @SuppressWarnings("unchecked")
      public void openFiles() throws FileLockException, IOException {
          files = new HeaderIndexFile[numberOfBuckets];
          cumulativeElementsPerFile = new int[numberOfBuckets];
          int lastfile = 0;
          String path = drums.getDatabaseDirectory();
          for (int i = 0; i < numberOfBuckets; i++) {
              String filename = path + "/" + drums.getHashFunction().getFilename(i);
              if (!new File(filename).exists()) {
                  cumulativeElementsPerFile[i] = 0;
              } else {
                  lastfile = i;
                  files[i] = new HeaderIndexFile<Data>(filename, 10, drums.gp);
                  cumulativeElementsPerFile[i] = (int) (files[i].getFilledUpFromContentStart() / elementSize);
              }
              if (i > 0) {
                  cumulativeElementsPerFile[i] += cumulativeElementsPerFile[i - 1];
              }
          }
  
          destBuffer = ByteBuffer.allocate((int) files[lastfile].getChunkSize());
          filesAreOpened = true;
      }
docs: Opens all files used by the underlying HashFunction. The pointers are stored in <code>files</code>.
  
  @throws FileLockException
  @throws IOException