# Package org.apache.hadoop.hdfs.util

- Interface Summary
  Interface | Description
  --- | ---
  Diff.Element<K> | An interface for the elements in a `Diff`.
  Diff.Processor<E> | An interface for passing a method in order to process elements.
  ReferenceCountMap.ReferenceCounter | Interface for the reference count holder
  RwLock | Read-write lock interface.

- Class Summary
  Class | Description
  --- | ---
  AtomicFileOutputStream | A FileOutputStream that has the property that it will only show up at its destination once it has been entirely written and flushed to disk.
  ConstEnumCounters<E extends Enum<E>> | Const Counters for an enum type.
  DataTransferThrottler | a class to throttle the data transfers.
  Diff<K,E extends Diff.Element<K>> | The difference between the current state and a previous state of a list.
  Diff.Container<E> | Containing exactly one element.
  Diff.UndoInfo<E> | Undo information for some operations such as delete(E) and `Diff.modify(Element, Element)`.
  EnumCounters<E extends Enum<E>> | Counters for an enum type.
  EnumDoubles<E extends Enum<E>> | Similar to `EnumCounters` except that the value type is double.
  Holder<T> | A Holder is simply a wrapper around some other object.
  LightWeightHashSet<T> | A low memory linked hash set implementation, which uses an array for storing the elements and linked lists for collision resolution.
  LightWeightLinkedSet<T> | A low memory linked hash set implementation, which uses an array for storing the elements and linked lists for collision resolution.
  MD5FileUtils | Static functions for dealing with files of the same format that the Unix "md5sum" utility writes.
  ReadOnlyList.Util | Utilities for `ReadOnlyList`
  XMLUtils.Stanza | Represents a bag of key-value pairs encountered during parsing an XML file.

- Exception Summary
  Exception | Description
  --- | ---
  ConstEnumCounters.ConstEnumException | An exception class for modification on ConstEnumCounters.
  XMLUtils.InvalidXmlException | Exception that reflects an invalid XML document.
  XMLUtils.UnmanglingError | Exception that reflects a string that cannot be unmangled.

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