Package org.apache.commons.collections.map

Class MultiKeyMap

java.lang.Object
org.apache.commons.collections.map.MultiKeyMap
All Implemented Interfaces:
Serializable, Map, IterableMap
public class MultiKeyMap extends Object implements IterableMap, Serializable
A Map implementation that uses multiple keys to map the value.

This class is the most efficient way to uses multiple keys to map to a value. The best way to use this class is via the additional map-style methods. These provide get, containsKey, put and remove for individual keys which operate without extra object creation.

The additional methods are the main interface of this map. As such, you will not normally hold this map in a variable of type Map.

The normal map methods take in and return a MultiKey. If you try to use put() with any other object type a ClassCastException is thrown. If you try to use null as the key in put() a NullPointerException is thrown.

This map is implemented as a decorator of a AbstractHashedMap which enables extra behaviour to be added easily.

  • MultiKeyMap.decorate(new LinkedMap()) creates an ordered map.
  • MultiKeyMap.decorate(new LRUMap()) creates an least recently used map.
  • MultiKeyMap.decorate(new ReferenceMap()) creates a garbage collector sensitive map.
Note that IdentityMap and ReferenceIdentityMap are unsuitable for use as the key comparison would work on the whole MultiKey, not the elements within.

As an example, consider a least recently used cache that uses a String airline code and a Locale to lookup the airline's name: 

 private MultiKeyMap cache = MultiKeyMap.decorate(new LRUMap(50));
 
 public String getAirlineName(String code, String locale) {
   String name = (String) cache.get(code, locale);
   if (name == null) {
     name = getAirlineNameFromDB(code, locale);
     cache.put(code, locale, name);
   }
   return name;
 }

Note that MultiKeyMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:
Commons Collections 3.1
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
Author:
Stephen Colebourne
See Also:

  • Field Details

  • Constructor Details

    • MultiKeyMap

      public MultiKeyMap()
      Constructs a new MultiKeyMap that decorates a HashedMap.

    • MultiKeyMap

      protected MultiKeyMap(AbstractHashedMap map)
      Constructor that decorates the specified map and is called from decorate(AbstractHashedMap). The map must not be null and should be empty or only contain valid keys. This constructor performs no validation.
      Parameters:
      map - the map to decorate

  • Method Details

    • decorate

      public static MultiKeyMap decorate(AbstractHashedMap map)
      Decorates the specified map to add the MultiKeyMap API and fast query. The map must not be null and must be empty.
      Parameters:
      map - the map to decorate, not null
      Throws:
      IllegalArgumentException - if the map is null or not empty

    • get

      public Object get(Object key1, Object key2)
      Gets the value mapped to the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      Returns:
      the mapped value, null if no match

    • containsKey

      public boolean containsKey(Object key1, Object key2)
      Checks whether the map contains the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      Returns:
      true if the map contains the key

    • put

      public Object put(Object key1, Object key2, Object value)
      Stores the value against the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      value - the value to store
      Returns:
      the value previously mapped to this combined key, null if none

    • removeMultiKey

      public Object removeMultiKey(Object key1, Object key2)
      Removes the specified multi-key from this map.
      Parameters:
      key1 - the first key
      key2 - the second key
      Returns:
      the value mapped to the removed key, null if key not in map

    • hash

      protected int hash(Object key1, Object key2)
      Gets the hash code for the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      Returns:
      the hash code

    • isEqualKey

      protected boolean isEqualKey(AbstractHashedMap.HashEntry entry, Object key1, Object key2)
      Is the key equal to the combined key.
      Parameters:
      entry - the entry to compare to
      key1 - the first key
      key2 - the second key
      Returns:
      true if the key matches

    • get

      public Object get(Object key1, Object key2, Object key3)
      Gets the value mapped to the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      Returns:
      the mapped value, null if no match

    • containsKey

      public boolean containsKey(Object key1, Object key2, Object key3)
      Checks whether the map contains the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      Returns:
      true if the map contains the key

    • put

      public Object put(Object key1, Object key2, Object key3, Object value)
      Stores the value against the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      value - the value to store
      Returns:
      the value previously mapped to this combined key, null if none

    • remove

      public Object remove(Object key1, Object key2, Object key3)
      Removes the specified multi-key from this map.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      Returns:
      the value mapped to the removed key, null if key not in map

    • hash

      protected int hash(Object key1, Object key2, Object key3)
      Gets the hash code for the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      Returns:
      the hash code

    • isEqualKey

      protected boolean isEqualKey(AbstractHashedMap.HashEntry entry, Object key1, Object key2, Object key3)
      Is the key equal to the combined key.
      Parameters:
      entry - the entry to compare to
      key1 - the first key
      key2 - the second key
      key3 - the third key
      Returns:
      true if the key matches

    • get

      public Object get(Object key1, Object key2, Object key3, Object key4)
      Gets the value mapped to the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      Returns:
      the mapped value, null if no match

    • containsKey

      public boolean containsKey(Object key1, Object key2, Object key3, Object key4)
      Checks whether the map contains the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      Returns:
      true if the map contains the key

    • put

      public Object put(Object key1, Object key2, Object key3, Object key4, Object value)
      Stores the value against the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      value - the value to store
      Returns:
      the value previously mapped to this combined key, null if none

    • remove

      public Object remove(Object key1, Object key2, Object key3, Object key4)
      Removes the specified multi-key from this map.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      Returns:
      the value mapped to the removed key, null if key not in map

    • hash

      protected int hash(Object key1, Object key2, Object key3, Object key4)
      Gets the hash code for the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      Returns:
      the hash code

    • isEqualKey

      protected boolean isEqualKey(AbstractHashedMap.HashEntry entry, Object key1, Object key2, Object key3, Object key4)
      Is the key equal to the combined key.
      Parameters:
      entry - the entry to compare to
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      Returns:
      true if the key matches

    • get

      public Object get(Object key1, Object key2, Object key3, Object key4, Object key5)
      Gets the value mapped to the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      key5 - the fifth key
      Returns:
      the mapped value, null if no match

    • containsKey

      public boolean containsKey(Object key1, Object key2, Object key3, Object key4, Object key5)
      Checks whether the map contains the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      key5 - the fifth key
      Returns:
      true if the map contains the key

    • put

      public Object put(Object key1, Object key2, Object key3, Object key4, Object key5, Object value)
      Stores the value against the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      key5 - the fifth key
      value - the value to store
      Returns:
      the value previously mapped to this combined key, null if none

    • remove

      public Object remove(Object key1, Object key2, Object key3, Object key4, Object key5)
      Removes the specified multi-key from this map.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      key5 - the fifth key
      Returns:
      the value mapped to the removed key, null if key not in map

    • hash

      protected int hash(Object key1, Object key2, Object key3, Object key4, Object key5)
      Gets the hash code for the specified multi-key.
      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      key5 - the fifth key
      Returns:
      the hash code

    • isEqualKey

      protected boolean isEqualKey(AbstractHashedMap.HashEntry entry, Object key1, Object key2, Object key3, Object key4, Object key5)
      Is the key equal to the combined key.
      Parameters:
      entry - the entry to compare to
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      key5 - the fifth key
      Returns:
      true if the key matches

    • removeAll

      public boolean removeAll(Object key1)
      Removes all mappings where the first key is that specified.

      This method removes all the mappings where the MultiKey has one or more keys, and the first matches that specified.

      Parameters:
      key1 - the first key
      Returns:
      true if any elements were removed

    • removeAll

      public boolean removeAll(Object key1, Object key2)
      Removes all mappings where the first two keys are those specified.

      This method removes all the mappings where the MultiKey has two or more keys, and the first two match those specified.

      Parameters:
      key1 - the first key
      key2 - the second key
      Returns:
      true if any elements were removed

    • removeAll

      public boolean removeAll(Object key1, Object key2, Object key3)
      Removes all mappings where the first three keys are those specified.

      This method removes all the mappings where the MultiKey has three or more keys, and the first three match those specified.

      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      Returns:
      true if any elements were removed

    • removeAll

      public boolean removeAll(Object key1, Object key2, Object key3, Object key4)
      Removes all mappings where the first four keys are those specified.

      This method removes all the mappings where the MultiKey has four or more keys, and the first four match those specified.

      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      Returns:
      true if any elements were removed

    • checkKey

      protected void checkKey(Object key)
      Check to ensure that input keys are valid MultiKey objects.
      Parameters:
      key - the key to check

    • clone

      public Object clone()
      Clones the map without cloning the keys or values.
      Overrides:
      clone in class Object
      Returns:
      a shallow clone

    • put

      public Object put(Object key, Object value)
      Puts the key and value into the map, where the key must be a non-null MultiKey object.
      Specified by:
      put in interface Map
      Parameters:
      key - the non-null MultiKey object
      value - the value to store
      Returns:
      the previous value for the key
      Throws:
      NullPointerException - if the key is null
      ClassCastException - if the key is not a MultiKey

    • putAll

      public void putAll(Map mapToCopy)
      Copies all of the keys and values from the specified map to this map. Each key must be non-null and a MultiKey object.
      Specified by:
      putAll in interface Map
      Parameters:
      mapToCopy - to this map
      Throws:
      NullPointerException - if the mapToCopy or any key within is null
      ClassCastException - if any key in mapToCopy is not a MultiKey

    • mapIterator

      public MapIterator mapIterator()
      Description copied from interface: IterableMap
      Obtains a MapIterator over the map.

      A map iterator is an efficient way of iterating over maps. There is no need to access the entry set or cast to Map Entry objects. 

       IterableMap map = new HashedMap();
 MapIterator it = map.mapIterator();
 while (it.hasNext()) {
   Object key = it.next();
   Object value = it.getValue();
   it.setValue("newValue");
 }
      Specified by:
      mapIterator in interface IterableMap
      Returns:
      a map iterator

    • size

      public int size()
      Specified by:
      size in interface Map

    • isEmpty

      public boolean isEmpty()
      Specified by:
      isEmpty in interface Map

    • containsKey

      public boolean containsKey(Object key)
      Specified by:
      containsKey in interface Map

    • containsValue

      public boolean containsValue(Object value)
      Specified by:
      containsValue in interface Map

    • get

      public Object get(Object key)
      Specified by:
      get in interface Map

    • remove

      public Object remove(Object key)
      Specified by:
      remove in interface Map

    • clear

      public void clear()
      Specified by:
      clear in interface Map

    • keySet

      public Set keySet()
      Specified by:
      keySet in interface Map

    • values

      public Collection values()
      Specified by:
      values in interface Map

    • entrySet

      public Set entrySet()
      Specified by:
      entrySet in interface Map

    • equals

      public boolean equals(Object obj)
      Specified by:
      equals in interface Map
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Specified by:
      hashCode in interface Map
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object