org.apache.commons.collections.list

Class LazyList

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.

Version:
$Revision: 1.6 $ $Date: 2004/06/03 22:02:13 $
Authors:
Stephen Colebourne
Arron Bates
Paul Jack
Since:
Commons Collections 3.0

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

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, get, getList, indexOf, lastIndexOf, listIterator, listIterator, remove, set, subList

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

Field Details

factory

protected final Factory factory
The factory to use to lazily instantiate the objects

Constructor Details

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

Method Details

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

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.

Overrides:
get in interface AbstractListDecorator
Parameters:
index - the index to retrieve

subList

public List subList(int fromIndex,
                    int toIndex)
Overrides:
subList in interface AbstractListDecorator

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