org.apache.commons.collections.list

Class LazyList

public class LazyList extends AbstractSerializableListDecorator

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

When the LazyList 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: 170244 $ $Date: 2005-05-15 19:30:49 +0100 (Sun, 15 May 2005) $

Author: Stephen Colebourne Arron Bates Paul Jack

See Also: GrowthList

Field Summary
protected Factoryfactory
The factory to use to lazily instantiate the objects
Constructor Summary
protected LazyList(List list, Factory factory)
Constructor that wraps (not copies).
Method Summary
static Listdecorate(List list, Factory factory)
Factory method to create a lazily instantiating list.
Objectget(int index)
Decorate the get method to perform the lazy behaviour.
ListsubList(int fromIndex, int toIndex)

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.

Parameters: index the index to retrieve

subList

public List subList(int fromIndex, int toIndex)
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