org.apache.commons.collections.list

## Class LazyList

- java.lang.Object
- - org.apache.commons.collections.collection.AbstractCollectionDecorator
  - - org.apache.commons.collections.list.AbstractListDecorator
    - - org.apache.commons.collections.list.AbstractSerializableListDecorator
      - - org.apache.commons.collections.list.LazyList

- All Implemented Interfaces:
    Serializable, Iterable, Collection, List

      public class LazyList
      extends AbstractSerializableListDecorator

  Decorates another `List` to create objects in the list on demand.

  When the `get(int)` method is called with an index greater than the size of the list, the list will automatically grow in size and return a new object from the specified factory. The gaps will be filled by null. If a get method call encounters a null, it will be replaced with a new object from the factory. Thus this list is unsuitable for storing null objects.

  For instance:

       Factory factory = new Factory() {
           public Object create() {
               return new Date();
           }
       }
       List lazy = LazyList.decorate(new ArrayList(), factory);
       Object obj = lazy.get(3);

  After the above code is executed, `obj` will contain a new `Date` instance. Furthermore, that `Date` instance is the fourth element in the list. The first, second, and third element are all set to `null`.

  This class differs from `GrowthList` because here growth occurs on get, where `GrowthList` grows on set and add. However, they could easily be used together by decorating twice.

  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) $
  Author:
    Stephen Colebourne, Arron Bates, Paul Jack
  See Also:
    `GrowthList`, Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected Factory` | `factory` The factory to use to lazily instantiate the objects

    - ### Fields inherited from class org.apache.commons.collections.collection.AbstractCollectionDecorator

      `collection`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `LazyList(List list, Factory factory)` Constructor that wraps (not copies).

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static List` | `decorate(List list, Factory factory)` Factory method to create a lazily instantiating list.
    `Object` | `get(int index)` Decorate the get method to perform the lazy behaviour.
    `List` | `subList(int fromIndex, int toIndex)`

    - ### Methods inherited from class org.apache.commons.collections.list.AbstractListDecorator

      `add, addAll, getList, indexOf, lastIndexOf, listIterator, listIterator, remove, set`

    - ### Methods inherited from class org.apache.commons.collections.collection.AbstractCollectionDecorator

      `add, addAll, clear, contains, containsAll, equals, getCollection, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface java.util.List

      `add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray`

- - ### Field Detail

    - #### factory

          protected final Factory factory

      The factory to use to lazily instantiate the objects

  - ### Constructor Detail

    - #### LazyList

          protected LazyList(List list,
                  Factory factory)

      Constructor that wraps (not copies).
      Parameters:
        `list` - the list to decorate, must not be null
        `factory` - the factory to use for creation, must not be null
      Throws:
        `IllegalArgumentException` - if list or factory is null

  - ### Method Detail

    - #### decorate

          public static List decorate(List list,
                      Factory factory)

      Factory method to create a lazily instantiating list.
      Parameters:
        `list` - the list to decorate, must not be null
        `factory` - the factory to use for creation, must not be null
      Throws:
        `IllegalArgumentException` - if list or factory is null

    - #### get

          public Object get(int index)

      Decorate the get method to perform the lazy behaviour.

      If the requested index is greater than the current size, the list will grow to the new size and a new object will be returned from the factory. Indexes in-between the old size and the requested size are left with a placeholder that is replaced with a factory object when requested.

      Specified by:
        `get` in interface `List`
      Overrides:
        `get` in class `AbstractListDecorator`
      Parameters:
        `index` - the index to retrieve

    - #### subList

          public List subList(int fromIndex,
                     int toIndex)

      Specified by:
        `subList` in interface `List`
      Overrides:
        `subList` in class `AbstractListDecorator`

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