Class LazyMap

  • All Implemented Interfaces:
    java.io.Serializable, java.util.Map
    Direct Known Subclasses:
    LazySortedMap

    public class LazyMap
    extends AbstractMapDecorator
    implements java.util.Map, 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 factory = new Factory() {
         public Object create() {
             return new Date();
         }
     }
     Map lazy = Lazy.map(new HashMap(), factory);
     Object obj = lazy.get("NOW");
     
    After the above code is executed, obj will contain 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:
    Commons Collections 3.0
    Version:
    $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
    See Also:
    Serialized Form
    • Nested Class Summary

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

        java.util.Map.Entry<K extends java.lang.Object,​V extends java.lang.Object>
    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      protected LazyMap​(java.util.Map map, Factory factory)
      Constructor that wraps (not copies).
      protected LazyMap​(java.util.Map map, Transformer factory)
      Constructor that wraps (not copies).
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static java.util.Map decorate​(java.util.Map map, Factory factory)
      Factory method to create a lazily instantiated map.
      static java.util.Map decorate​(java.util.Map map, Transformer factory)
      Factory method to create a lazily instantiated map.
      java.lang.Object get​(java.lang.Object key)  
      private void readObject​(java.io.ObjectInputStream in)
      Read the map in using a custom routine.
      private void writeObject​(java.io.ObjectOutputStream out)
      Write the map out using a custom routine.
      • Methods inherited from class java.lang.Object

        clone, finalize, getClass, notify, notifyAll, wait, wait, wait
      • Methods inherited from interface java.util.Map

        clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, equals, forEach, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values
    • Field Detail

      • serialVersionUID

        private static final long serialVersionUID
        Serialization version
        See Also:
        Constant Field Values
      • factory

        protected final Transformer factory
        The factory to use to construct elements
    • Constructor Detail

      • LazyMap

        protected LazyMap​(java.util.Map map,
                          Factory factory)
        Constructor that wraps (not copies).
        Parameters:
        map - the map to decorate, must not be null
        factory - the factory to use, must not be null
        Throws:
        java.lang.IllegalArgumentException - if map or factory is null
      • LazyMap

        protected LazyMap​(java.util.Map map,
                          Transformer factory)
        Constructor that wraps (not copies).
        Parameters:
        map - the map to decorate, must not be null
        factory - the factory to use, must not be null
        Throws:
        java.lang.IllegalArgumentException - if map or factory is null
    • Method Detail

      • decorate

        public static java.util.Map decorate​(java.util.Map map,
                                             Factory factory)
        Factory method to create a lazily instantiated map.
        Parameters:
        map - the map to decorate, must not be null
        factory - the factory to use, must not be null
        Throws:
        java.lang.IllegalArgumentException - if map or factory is null
      • decorate

        public static java.util.Map decorate​(java.util.Map map,
                                             Transformer factory)
        Factory method to create a lazily instantiated map.
        Parameters:
        map - the map to decorate, must not be null
        factory - the factory to use, must not be null
        Throws:
        java.lang.IllegalArgumentException - if map or factory is null
      • writeObject

        private void writeObject​(java.io.ObjectOutputStream out)
                          throws java.io.IOException
        Write the map out using a custom routine.
        Parameters:
        out - the output stream
        Throws:
        java.io.IOException
        Since:
        Commons Collections 3.1
      • readObject

        private void readObject​(java.io.ObjectInputStream in)
                         throws java.io.IOException,
                                java.lang.ClassNotFoundException
        Read the map in using a custom routine.
        Parameters:
        in - the input stream
        Throws:
        java.io.IOException
        java.lang.ClassNotFoundException
        Since:
        Commons Collections 3.1
      • get

        public java.lang.Object get​(java.lang.Object key)
        Specified by:
        get in interface java.util.Map
        Overrides:
        get in class AbstractMapDecorator