de.unkrig.commons.lang.protocol

Class Mapping<K,V>

java.lang.Object

de.unkrig.commons.lang.protocol.Mapping<K,V>

Type Parameters:

K - The 'key' type

V - The 'value' type

public abstract class Mapping<K,V>
extends java.lang.Object

A map that computes a value only when get(Object) is invoked. Consequently, in contrast with Map, it has no specific size(), and thus no entrySet(), keySet() and values() set. Also the modifying operations (put, putAll, remove and clear) are all missing, because a Mapping is not changed by "putting" key-value-pairs into it.

Actually Map should extend Mapping, but it doesn't - thus there are the asMap() and Mappings.fromMap(Map) helper methods.

The relationship between Mapping and Map is very much like that between Predicate and Collection.

IMPORTANT NOTICE:

When using this type in a variable, parameter or field declaration, never write:

Mapping<key-type, value-type>

, but always:

Mapping<? super key-type, ? extends value-type>

That way many type conversions are possible which otherwise aren't.

Constructor Summary

Constructors

Constructor and Description
Mapping()

Method Summary

Modifier and Type	Method and Description
java.util.Map<K,V>	asMap() Returns a proxy Map for a Mapping where all methods declared by Map but not by Mapping throw an UnsupportedOperationException.
abstract boolean	containsKey(java.lang.Object key)
abstract V	get(java.lang.Object key)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Mapping

public Mapping()

Method Detail

containsKey

public abstract boolean containsKey(@Nullable
                                    java.lang.Object key)

See Also:

Map.containsKey(Object)

get

@Nullable
public abstract V get(@Nullable
                                 java.lang.Object key)

See Also:

Map.get(Object)

asMap

public final java.util.Map<K,V> asMap()

Returns a proxy Map for a Mapping where all methods declared by Map but not by Mapping throw an UnsupportedOperationException.