Class DefaultMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

java.util.HashMap<K,V>

uk.ac.manchester.spinnaker.utils.DefaultMap<K,V>

Type Parameters:

K - The type of keys.

V - The type of values.

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>

public class DefaultMap<K,V>
extends HashMap<K,V>

A map that will extend itself with new values (on get) when the key is otherwise absent from the map. Note that this map is only safely serializable if the default value is literal and serializable, in addition to the usual constraints of maps.

Author:

Donal Fellows

See Also:

• Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	DefaultMap.KeyAwareFactory<K,V>	An advanced factory that has access to the key when it is creating the value to associate with it.

Nested classes/interfaces inherited from class AbstractMap

AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

Nested classes/interfaces inherited from interface Map

Map.Entry<K,V>

Constructor Summary

Constructors

Constructor	Description
DefaultMap(Supplier<? extends V> defaultFactory)	Create a new map.

Method Summary

Modifier and Type	Method	Description
V	compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
V	computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction)
V	computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
V	get(Object key)	Gets a value from the dictionary, inserting a newly manufactured value if the key has no mapping.
V	merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction)
static <K,V> DefaultMap<K,V>	newAdvancedDefaultMap(DefaultMap.KeyAwareFactory<? super K, ? extends V> keyAwareFactory)	Create a new map that manufactures new elements that are aware of their key from the beginning.
static <K,DV> DefaultMap<K,DV>	newMapWithDefault(DV defaultValue)	Create a new map.

Methods inherited from class HashMap

clear, clone, containsKey, containsValue, entrySet, forEach, getOrDefault, isEmpty, keySet, newHashMap, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values

Methods inherited from class AbstractMap

equals, hashCode, toString

Methods inherited from class Object

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

Methods inherited from interface Map

equals, hashCode

Constructor Details

DefaultMap

public DefaultMap(Supplier<? extends V> defaultFactory)

Create a new map.

The defaultFactory is a method to generate an object. If the default value is mutable it is highly recommended to pass in a method like this, and not an object. For example use ArrayList::new and not new ArrayList() otherwise the single value will be used every time and values added after one get will be in the default for the next get.

Parameters:

defaultFactory - A method to create a new value/object to insert in the map.

Method Details

newMapWithDefault

public static <K,DV> DefaultMap<K,DV> newMapWithDefault(DV defaultValue)

Create a new map.

Type Parameters:

K - The type of keys.

DV - The type of the default value.

Parameters:

defaultValue - The default value to use in the map. This should be an immutable value as it can be potentially inserted for many keys. Must not be null.

Returns:

The new default map.

newAdvancedDefaultMap

public static <K,V> DefaultMap<K,V> newAdvancedDefaultMap(DefaultMap.KeyAwareFactory<? super K, ? extends V> keyAwareFactory)

Create a new map that manufactures new elements that are aware of their key from the beginning. This is done through this method because otherwise it clashes with the more common case of the unaware factory.

The Factory can be a lambda method to create a me value based on the key.
For example:

DefaultMap.newAdvancedDefaultMap(i -> i*2);

The Factory can also be a Object of a class that implements the KeyAwareFactory interface.

Type Parameters:

K - The type of keys.

V - The type of values.

Parameters:

keyAwareFactory - Method or Object to create the default values.

Returns:

The new default map.

get

public V get(Object key)

Gets a value from the dictionary, inserting a newly manufactured value if the key has no mapping.

Specified by:

get in interface Map<K,V>

Overrides:

get in class HashMap<K,V>

compute

public V compute(K key,
 BiFunction<? super K, ? super V, ? extends V> remappingFunction)

NB: This converts nulls into the correct default value.

Specified by:

compute in interface Map<K,V>

Overrides:

compute in class HashMap<K,V>

computeIfAbsent

public V computeIfAbsent(K key,
 Function<? super K, ? extends V> mappingFunction)

NB: This converts nulls into the correct default value.

Specified by:

computeIfAbsent in interface Map<K,V>

Overrides:

computeIfAbsent in class HashMap<K,V>

computeIfPresent

public V computeIfPresent(K key,
 BiFunction<? super K, ? super V, ? extends V> remappingFunction)

NB: This converts nulls into the correct default value.

Specified by:

computeIfPresent in interface Map<K,V>

Overrides:

computeIfPresent in class HashMap<K,V>

merge

public V merge(K key,
 V value,
 BiFunction<? super V, ? super V, ? extends V> remappingFunction)

NB: This converts nulls into the correct default value.

Specified by:

merge in interface Map<K,V>

Overrides:

merge in class HashMap<K,V>