org.apache.commons.collections4.map

Class LazyMap<K,V>

java.lang.Object

org.apache.commons.collections4.map.AbstractIterableMap<K,V>

org.apache.commons.collections4.map.AbstractMapDecorator<K,V>

org.apache.commons.collections4.map.LazyMap<K,V>

Type Parameters:

K - the type of the keys in this map

V - the type of the values in this map

All Implemented Interfaces:

java.io.Serializable, java.util.Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Put<K,V>

Direct Known Subclasses:

LazySortedMap

public class LazyMap<K,V>
extends AbstractMapDecorator<K,V>
implements java.io.Serializable

Decorates another Map to create objects in the map on demand.

When the get(Object) method is called with a key that does not exist in the map, the factory is used to create the object. The created object will be added to the map using the requested key.

For instance:

 Factory<Date> factory = new Factory<Date>() {
     public Date create() {
         return new Date();
     }
 }
 Map<String, Date> lazy = LazyMap.lazyMap(new HashMap<String, Date>(), factory);
 Date date = lazy.get("NOW");
 

After the above code is executed, date will refer to a new Date instance. Furthermore, that Date instance is mapped to the "NOW" key in the map.

Note that LazyMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

This class is Serializable from Commons Collections 3.1.

Since:

3.0

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Method Summary

Modifier and Type	Method and Description
V	get(java.lang.Object key)
static <K,V> LazyMap<K,V>	lazyMap(java.util.Map<K,V> map, Factory<? extends V> factory) Factory method to create a lazily instantiated map.
static <V,K> LazyMap<K,V>	lazyMap(java.util.Map<K,V> map, Transformer<? super K,? extends V> factory) Factory method to create a lazily instantiated map.

Methods inherited from class org.apache.commons.collections4.map.AbstractMapDecorator

clear, containsKey, containsValue, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values

Methods inherited from class org.apache.commons.collections4.map.AbstractIterableMap

mapIterator

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

Method Detail

lazyMap

public static <K,V> LazyMap<K,V> lazyMap(java.util.Map<K,V> map,
                                         Factory<? extends V> factory)

Factory method to create a lazily instantiated map.

Type Parameters:

K - the key type

V - the value type

Parameters:

map - the map to decorate, must not be null

factory - the factory to use, must not be null

Returns:

a new lazy map

Throws:

java.lang.NullPointerException - if map or factory is null

Since:

4.0

lazyMap

public static <V,K> LazyMap<K,V> lazyMap(java.util.Map<K,V> map,
                                         Transformer<? super K,? extends V> factory)

Factory method to create a lazily instantiated map.

Type Parameters:

K - the key type

V - the value type

Parameters:

map - the map to decorate, must not be null

factory - the factory to use, must not be null

Returns:

a new lazy map

Throws:

java.lang.NullPointerException - if map or factory is null

Since:

4.0

get

public V get(java.lang.Object key)

Specified by:

get in interface java.util.Map<K,V>

Specified by:

get in interface Get<K,V>

Overrides:

get in class AbstractMapDecorator<K,V>

Parameters:

key - the key whose associated value is to be returned

Returns:

the value to which the specified key is mapped, or null if this map contains no mapping for the key

See Also:

Map.get(Object)