Apache Commons Collections 4.4 · org.apache.commons.collections4.map.LazyMap

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 java.util.Collections#synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

This class is Serializable from Commons Collections 3.1.

Field Summary

Modifier and Type	Field and Description
protected final Transformer<? super K, ? extends V>	factory The factory to use to construct elements
private static final long	serialVersionUID Serialization version

Inherited from org.apache.commons.collections4.map.AbstractMapDecorator:: map

Access	Constructor and Description
protected	LazyMap(final Map<K, V> the map to decorate, must not be null map, final Factory<? extends V> the factory to use, must not be null factory) Constructor that wraps (not copies).
protected	LazyMap(final Map<K, V> the map to decorate, must not be null map, final Transformer<? super K, ? extends V> the factory to use, must not be null factory) Constructor that wraps (not copies).

Method Summary

Modifier and Type	Method and Description
public V	get(final Object the key whose associated value is to be returned key) Overrides org.apache.commons.collections4.map.AbstractMapDecorator.get. Implements java.util.Map.get, org.apache.commons.collections4.Get.get. Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key.
public static < the key type K, the value type V> LazyMap<K, V>	Returns: a new lazy map lazyMap(final Map<K, V> the map to decorate, must not be null map, final Factory<? extends V> the factory to use, must not be null factory) Factory method to create a lazily instantiated map.
public static < the value type V, the key type K> LazyMap<K, V>	Returns: a new lazy map lazyMap(final Map<K, V> the map to decorate, must not be null map, final Transformer<? super K, ? extends V> the factory to use, must not be null factory) Factory method to create a lazily instantiated map.
private void	readObject(final ObjectInputStream the input stream in) Read the map in using a custom routine.
private void	writeObject(final ObjectOutputStream the output stream out) Write the map out using a custom routine.

Inherited from org.apache.commons.collections4.map.AbstractMapDecorator:: clear containsKey containsValue decorated entrySet equals hashCode isEmpty keySet put putAll remove size toString values

Field Detail

factory	back to summary
protected final Transformer<? super K, ? extends V> factory The factory to use to construct elements

serialVersionUID	back to summary
private static final long serialVersionUID Serialization version

Constructor Detail

LazyMap	back to summary
protected LazyMap(final Map<K, V> map, final Factory<? extends V> factory) Constructor that wraps (not copies). Parameters map:Map<K, V> the map to decorate, must not be null factory:Factory<? extends V> the factory to use, must not be null Exceptions NullPointerException: if map or factory is null

LazyMap

back to summary

protected LazyMap(final Map<K, V> map, final Factory<? extends V> factory)

Constructor that wraps (not copies).

Parameters

map:Map<K, V>: the map to decorate, must not be null
factory:Factory<? extends V>: the factory to use, must not be null

Exceptions

NullPointerException:: if map or factory is null

LazyMap	back to summary
protected LazyMap(final Map<K, V> map, final Transformer<? super K, ? extends V> factory) Constructor that wraps (not copies). Parameters map:Map<K, V> the map to decorate, must not be null factory:Transformer<? super K, ? extends V> the factory to use, must not be null Exceptions NullPointerException: if map or factory is null

LazyMap

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protected LazyMap(final Map<K, V> map, final Transformer<? super K, ? extends V> factory)

Constructor that wraps (not copies).

Parameters

map:Map<K, V>: the map to decorate, must not be null
factory:Transformer<? super K, ? extends V>: the factory to use, must not be null

Exceptions

NullPointerException:: if map or factory is null

Method Detail

get back to summary

get	back to summary
public V get(final Object key) Overrides org.apache.commons.collections4.map.AbstractMapDecorator.get. Implements java.util.Map.get, org.apache.commons.collections4.Get.get. Doc from java.util.Map.get. Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key. More formally, if this map contains a mapping from a key `k` to a value `v` such that `Objects.equals(key, k)`, then this method returns `v`; otherwise it returns `null`. (There can be at most one such mapping.) If this map permits null values, then a return value of `null` does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to `null`. The `containsKey` operation may be used to distinguish these two cases. Parameters key:Object the key whose associated value is to be returned Returns:V the value to which the specified key is mapped, or `null` if this map contains no mapping for the key Annotations @Override

public V get(final Object key)

Overrides org.apache.commons.collections4.map.AbstractMapDecorator.get.

Implements java.util.Map.get, org.apache.commons.collections4.Get.get.

Doc from java.util.Map.get.

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

More formally, if this map contains a mapping from a key k to a value v such that Objects.equals(key, k), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

If this map permits null values, then a return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Parameters

key:Object: the key whose associated value is to be returned

Returns:V

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

Annotations

@Override

lazyMap	back to summary
public static <K, V> LazyMap<K, V> lazyMap(final Map<K, V> map, final Factory<? extends V> factory) Factory method to create a lazily instantiated map. Parameters <K> the key type <V> the value type map:Map<K, V> the map to decorate, must not be null factory:Factory<? extends V> the factory to use, must not be null Returns:LazyMap<K, V> a new lazy map Exceptions NullPointerException: if map or factory is null Since 4.0

lazyMap

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

Factory method to create a lazily instantiated map.

Parameters

<K>: the key type
<V>: the value type
map:Map<K, V>: the map to decorate, must not be null
factory:Factory<? extends V>: the factory to use, must not be null

Returns:LazyMap<K, V>

a new lazy map

Exceptions

NullPointerException:: if map or factory is null

Since

4.0

lazyMap	back to summary
public static <V, K> LazyMap<K, V> lazyMap(final Map<K, V> map, final Transformer<? super K, ? extends V> factory) Factory method to create a lazily instantiated map. Parameters <V> the value type <K> the key type map:Map<K, V> the map to decorate, must not be null factory:Transformer<? super K, ? extends V> the factory to use, must not be null Returns:LazyMap<K, V> a new lazy map Exceptions NullPointerException: if map or factory is null Since 4.0

lazyMap

back to summary

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

Factory method to create a lazily instantiated map.

Parameters

<V>: the value type
<K>: the key type
map:Map<K, V>: the map to decorate, must not be null
factory:Transformer<? super K, ? extends V>: the factory to use, must not be null

Returns:LazyMap<K, V>

a new lazy map

Exceptions

NullPointerException:: if map or factory is null

Since

4.0

readObject	back to summary
private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException Read the map in using a custom routine. Parameters in:ObjectInputStream the input stream Annotations @SuppressWarnings:unchecked Exceptions IOException: if an error occurs while reading from the stream ClassNotFoundException: if an object read from the stream can not be loaded Since 3.1

readObject

back to summary

private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException

Read the map in using a custom routine.

Parameters

in:ObjectInputStream: the input stream

Annotations

@SuppressWarnings:unchecked

Exceptions

IOException:: if an error occurs while reading from the stream
ClassNotFoundException:: if an object read from the stream can not be loaded

Since

3.1

writeObject	back to summary
private void writeObject(final ObjectOutputStream out) throws IOException Write the map out using a custom routine. Parameters out:ObjectOutputStream the output stream Exceptions IOException: if an error occurs while writing to the stream Since 3.1

writeObject

back to summary

private void writeObject(final ObjectOutputStream out) throws IOException

Write the map out using a custom routine.

Parameters

out:ObjectOutputStream: the output stream

Exceptions

IOException:: if an error occurs while writing to the stream

Since

3.1

public Class LazyMap<K, V>

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail