## 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:
  Collection, List, Serializable

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 is Serializable from Commons Collections 3.1.

Since:
  Commons Collections 3.0
Version:
  $Revision: 1.6 $ $Date: 2004/06/03 22:02:13 $
Author:
  Stephen Colebourne, Arron Bates, Paul Jack
See Also:
  Serialized Form

Field Summary
`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
`protected` `LazyList(List list, Factory factory)` Constructor that wraps (not copies).

Method Summary
`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`

Copyright © 2001-2005 Apache Software Foundation. All Rights Reserved.