@Override
  public void init(Map<String, Object> params) {
    // subclass could override it if needed.
  }
Base class for file cleaners which allows subclasses to implement a simple isFileDeletable method
(which used to be the FileCleanerDelegate contract).
hbase-server/src/main/java/org/apache/hadoop/hbase/master/cleaner/BaseFileCleanerDelegate.java