Package org.apache.commons.collections4.keyvalue

Class MultiKey<K>

java.lang.Object
org.apache.commons.collections4.keyvalue.MultiKey<K>
Type Parameters:
K - the type of keys
All Implemented Interfaces:
Serializable
public class MultiKey<K> extends Object implements Serializable
A MultiKey allows multiple map keys to be merged together.

The purpose of this class is to avoid the need to write code to handle maps of maps. An example might be the need to look up a file name by key and locale. The typical solution might be nested maps. This class can be used instead by creating an instance passing in the key and locale.

Example usage: 

 // populate map with data mapping key+locale to localizedText
 Map map = new HashMap();
 MultiKey multiKey = new MultiKey(key, locale);
 map.put(multiKey, localizedText);

 // later retrieve the localized text
 MultiKey multiKey = new MultiKey(key, locale);
 String localizedText = (String) map.get(multiKey);
Since:
3.0
See Also:

  • Constructor Summary

    Constructors
    Constructor
    Description
    MultiKey(K[] keys)
    Constructor taking an array of keys which is cloned.
    MultiKey(K[] keys, boolean makeClone)
    Constructor taking an array of keys, optionally choosing whether to clone.
    MultiKey(K key1, K key2)
    Constructor taking two keys.
    MultiKey(K key1, K key2, K key3)
    Constructor taking three keys.
    MultiKey(K key1, K key2, K key3, K key4)
    Constructor taking four keys.
    MultiKey(K key1, K key2, K key3, K key4, K key5)
    Constructor taking five keys.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    equals(Object other)
    Compares this object to another.
    K
    getKey(int index)
    Gets the key at the specified index.
    K[]
    getKeys()
    Gets a clone of the array of keys.
    int
    hashCode()
    Gets the combined hash code that is computed from all the keys.
    protected Object
    readResolve()
    Recalculate the hash code after deserialization.
    int
    size()
    Gets the size of the list of keys.
    String
    toString()
    Gets a debugging string version of the key.

    Methods inherited from class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

  • Constructor Details

    • MultiKey

      public MultiKey(K key1, K key2)
      Constructor taking two keys.

      The keys should be immutable. If they are not then they must not be changed after adding to the MultiKey.

      Parameters:
      key1 - the first key
      key2 - the second key

    • MultiKey

      public MultiKey(K key1, K key2, K key3)
      Constructor taking three keys.

      The keys should be immutable If they are not then they must not be changed after adding to the MultiKey.

      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key

    • MultiKey

      public MultiKey(K key1, K key2, K key3, K key4)
      Constructor taking four keys.

      The keys should be immutable. If they are not then they must not be changed after adding to the MultiKey.

      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key

    • MultiKey

      public MultiKey(K key1, K key2, K key3, K key4, K key5)
      Constructor taking five keys.

      The keys should be immutable. If they are not then they must not be changed after adding to the MultiKey.

      Parameters:
      key1 - the first key
      key2 - the second key
      key3 - the third key
      key4 - the fourth key
      key5 - the fifth key

    • MultiKey

      public MultiKey(K[] keys)
      Constructor taking an array of keys which is cloned.

      The keys should be immutable. If they are not then they must not be changed after adding to the MultiKey.

      This is equivalent to new MultiKey(keys, true).

      Parameters:
      keys - the array of keys, not null
      Throws:
      NullPointerException - if the key array is null

    • MultiKey

      public MultiKey(K[] keys, boolean makeClone)
      Constructor taking an array of keys, optionally choosing whether to clone.

      If the array is not cloned, then it must not be modified.

      This method is public for performance reasons only, to avoid a clone. The hash code is calculated once here in this method. Therefore, changing the array passed in would not change the hash code but would change the equals method, which is a bug.

      This is the only fully safe usage of this constructor, as the object array is never made available in a variable: 

       new MultiKey(new Object[] {...}, false);

      The keys should be immutable. If they are not then they must not be changed after adding to the MultiKey.

      Parameters:
      keys - the array of keys, not null
      makeClone - true to clone the array, false to assign it
      Throws:
      NullPointerException - if the key array is null
      Since:
      3.1

  • Method Details

    • equals

      public boolean equals(Object other)
      Compares this object to another.

      To be equal, the other object must be a MultiKey with the same number of keys which are also equal.

      Overrides:
      equals in class Object
      Parameters:
      other - the other object to compare to
      Returns:
      true if equal

    • getKey

      public K getKey(int index)
      Gets the key at the specified index.

      The key should be immutable. If it is not then it must not be changed.

      Parameters:
      index - the index to retrieve
      Returns:
      the key at the index
      Throws:
      IndexOutOfBoundsException - if the index is invalid
      Since:
      3.1

    • getKeys

      public K[] getKeys()
      Gets a clone of the array of keys.

      The keys should be immutable If they are not then they must not be changed.

      Returns:
      the individual keys

    • hashCode

      public int hashCode()
      Gets the combined hash code that is computed from all the keys.

      This value is computed once and then cached, so elements should not change their hash codes once created (note that this is the same constraint that would be used if the individual keys elements were themselves Map keys).

      Overrides:
      hashCode in class Object
      Returns:
      the hash code

    • readResolve

      protected Object readResolve()
      Recalculate the hash code after deserialization. The hash code of some keys might have change (hash codes based on the system hash code are only stable for the same process).
      Returns:
      the instance with recalculated hash code

    • size

      public int size()
      Gets the size of the list of keys.
      Returns:
      the size of the list of keys
      Since:
      3.1

    • toString

      public String toString()
      Gets a debugging string version of the key.
      Overrides:
      toString in class Object
      Returns:
      a debugging string