Package org.apache.commons.collections

Class LRUMap

java.lang.Object
org.apache.commons.collections.SequencedHashMap
org.apache.commons.collections.LRUMap
All Implemented Interfaces:
Externalizable, Serializable, Cloneable, Map
@Deprecated(since="2021-04-30") public class LRUMap extends SequencedHashMap implements Externalizable
Deprecated.
Moved to map subpackage. Due to be removed in v4.0.

An implementation of a Map which has a maximum size and uses a Least Recently Used algorithm to remove items from the Map when the maximum size is reached and new items are added.

A synchronized version can be obtained with: Collections.synchronizedMap( theMapToSynchronize ) If it will be accessed by multiple threads, you _must_ synchronize access to this Map. Even concurrent get(Object) operations produce indeterminate behaviour.

Unlike the Collections 1.0 version, this version of LRUMap does use a true LRU algorithm. The keys for all gets and puts are moved to the front of the list. LRUMap is now a subclass of SequencedHashMap, and the "LRU" key is now equivalent to LRUMap.getFirst().

Since:
Commons Collections 1.0
See Also:

  • Constructor Details

    • LRUMap

      public LRUMap()
      Deprecated.
      Default constructor, primarily for the purpose of de-externalization. This constructors sets a default LRU limit of 100 keys, but this value may be overridden internally as a result of de-externalization.

    • LRUMap

      public LRUMap(int i)
      Deprecated.
      Create a new LRUMap with a maximum capacity of i. Once i capacity is achieved, subsequent gets and puts will push keys out of the map. See .
      Parameters:
      i - Maximum capacity of the LRUMap

  • Method Details

    • get

      public Object get(Object key)
      Deprecated.

      Get the value for a key from the Map. The key will be promoted to the Most Recently Used position. Note that get(Object) operations will modify the underlying Collection. Calling get(Object) inside of an iteration over keys, values, etc. is currently unsupported.

      Specified by:
      get in interface Map
      Overrides:
      get in class SequencedHashMap
      Parameters:
      key - Key to retrieve
      Returns:
      Returns the value. Returns null if the key has a null value or if the key has no value.

    • put

      public Object put(Object key, Object value)
      Deprecated.

      Removes the key and its Object from the Map.

      (Note: this may result in the "Least Recently Used" object being removed from the Map. In that case, the removeLRU() method is called. See javadoc for removeLRU() for more details.)

      Specified by:
      put in interface Map
      Overrides:
      put in class SequencedHashMap
      Parameters:
      key - Key of the Object to add.
      value - Object to add
      Returns:
      Former value of the key

    • readExternal

      public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
      Deprecated.
      Description copied from class: SequencedHashMap
      Deserializes this map from the given stream.
      Specified by:
      readExternal in interface Externalizable
      Overrides:
      readExternal in class SequencedHashMap
      Parameters:
      in - the stream to deserialize from
      Throws:
      IOException - if the stream raises it
      ClassNotFoundException - if the stream raises it

    • writeExternal

      public void writeExternal(ObjectOutput out) throws IOException
      Deprecated.
      Description copied from class: SequencedHashMap
      Serializes this map to the given stream.
      Specified by:
      writeExternal in interface Externalizable
      Overrides:
      writeExternal in class SequencedHashMap
      Parameters:
      out - the stream to serialize to
      Throws:
      IOException - if the stream raises it

    • getMaximumSize

      public int getMaximumSize()
      Deprecated.
      Getter for property maximumSize.
      Returns:
      Value of property maximumSize.

    • setMaximumSize

      public void setMaximumSize(int maximumSize)
      Deprecated.
      Setter for property maximumSize.
      Parameters:
      maximumSize - New value of property maximumSize.