Class LRUMap

Method Details

• get

  public Object get(Object key)

  Gets the value mapped to the key specified.

  This operation changes the position of the key in the map to the most recently used position (first).

  Specified by:

  get in interface Map

  Overrides:

  get in class AbstractHashedMap

  Parameters:

  key - the key

  Returns:

  the mapped value, null if no match

• moveToMRU

  protected void moveToMRU(AbstractLinkedMap.LinkEntry entry)

  Moves an entry to the MRU position at the end of the list.

  This implementation moves the updated entry to the end of the list.

  Parameters:

  entry - the entry to update

• updateEntry

  protected void updateEntry(AbstractHashedMap.HashEntry entry, Object newValue)

  Updates an existing key-value mapping.

  This implementation moves the updated entry to the top of the list using moveToMRU(AbstractLinkedMap.LinkEntry).

  Overrides:

  updateEntry in class AbstractHashedMap

  Parameters:

  entry - the entry to update

  newValue - the new value to store

• addMapping

  protected void addMapping(int hashIndex, int hashCode, Object key, Object value)

  Adds a new key-value mapping into this map.

  This implementation checks the LRU size and determines whether to discard an entry or not using removeLRU(AbstractLinkedMap.LinkEntry).

  From Commons Collections 3.1 this method uses isFull() rather than accessing size and maxSize directly. It also handles the scanUntilRemovable functionality.

  Overrides:

  addMapping in class AbstractHashedMap

  Parameters:

  hashIndex - the index into the data array to store at

  hashCode - the hash code of the key to add

  key - the key to add

  value - the value to add

• reuseMapping

  protected void reuseMapping(AbstractLinkedMap.LinkEntry entry, int hashIndex, int hashCode, Object key, Object value)

  Reuses an entry by removing it and moving it to a new place in the map.

  This method uses AbstractLinkedMap.removeEntry(org.apache.commons.collections.map.AbstractHashedMap.HashEntry, int, org.apache.commons.collections.map.AbstractHashedMap.HashEntry), AbstractHashedMap.reuseEntry(org.apache.commons.collections.map.AbstractHashedMap.HashEntry, int, int, java.lang.Object, java.lang.Object) and AbstractLinkedMap.addEntry(org.apache.commons.collections.map.AbstractHashedMap.HashEntry, int).

  Parameters:

  entry - the entry to reuse

  hashIndex - the index into the data array to store at

  hashCode - the hash code of the key to add

  key - the key to add

  value - the value to add

• removeLRU

  protected boolean removeLRU(AbstractLinkedMap.LinkEntry entry)

  Subclass method to control removal of the least recently used entry from the map.

  This method exists for subclasses to override. A subclass may wish to provide cleanup of resources when an entry is removed. For example:

   protected boolean removeLRU(LinkEntry entry) {
     releaseResources(entry.getValue());  // release resources held by entry
     return true;  // actually delete entry
   }
   

  Alternatively, a subclass may choose to not remove the entry or selectively keep certain LRU entries. For example:

   protected boolean removeLRU(LinkEntry entry) {
     if (entry.getKey().toString().startsWith("System.")) {
       return false;  // entry not removed from LRUMap
     } else {
       return true;  // actually delete entry
     }
   }
   

  The effect of returning false is dependent on the scanUntilRemovable flag. If the flag is true, the next LRU entry will be passed to this method and so on until one returns false and is removed, or every entry in the map has been passed. If the scanUntilRemovable flag is false, the map will exceed the maximum size.

  NOTE: Commons Collections 3.0 passed the wrong entry to this method. This is fixed in version 3.1 onwards.

  Parameters:

  entry - the entry to be removed

• isFull

  public boolean isFull()

  Returns true if this map is full and no new mappings can be added.

  Specified by:

  isFull in interface BoundedMap

  Returns:

  true if the map is full

• maxSize

  public int maxSize()

  Gets the maximum size of the map (the bound).

  Specified by:

  maxSize in interface BoundedMap

  Returns:

  the maximum number of elements the map can hold

• isScanUntilRemovable

  public boolean isScanUntilRemovable()

  Whether this LRUMap will scan until a removable entry is found when the map is full.

  Returns:

  true if this map scans

  Since:

  Commons Collections 3.1

• clone

  public Object clone()

  Clones the map without cloning the keys or values.

  Overrides:

  clone in class AbstractHashedMap

  Returns:

  a shallow clone

• doWriteObject

  protected void doWriteObject(ObjectOutputStream out) throws IOException

  Writes the data necessary for put() to work in deserialization.

  Overrides:

  doWriteObject in class AbstractHashedMap

  Parameters:

  out - the output stream

  Throws:

  IOException

• doReadObject

  protected void doReadObject(ObjectInputStream in) throws IOException, ClassNotFoundException

  Reads the data necessary for put() to work in the superclass.

  Overrides:

  doReadObject in class AbstractHashedMap

  Parameters:

  in - the input stream

  Throws:

  IOException

  ClassNotFoundException