org.apache.commons.collections.list
public class LazyList extends AbstractSerializableListDecorator
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) $
See Also: GrowthList
Field Summary | |
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protected Factory | factory The factory to use to lazily instantiate the objects |
Constructor Summary | |
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protected | LazyList(List list, Factory factory)
Constructor that wraps (not copies).
|
Method Summary | |
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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) |
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
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
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