@Override
      public List<HStoreFile> next() {
        List<HStoreFile> files = createStoreFileList(fileSizes[nextIndex]);
        nextIndex += 1;
        return files;
      }
The explicit files size lists to return.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/compactions/ExplicitFileListGenerator.java