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.LazyList
- All Implemented Interfaces:
- Collection, List
- public class LazyList
- extends AbstractListDecorator
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
.
- Since:
- Commons Collections 3.0
- Version:
- $Revision: 1.3 $ $Date: 2004/01/14 21:43:17 $
- Author:
- Stephen Colebourne, Arron Bates, Paul Jack
Field Summary |
protected Factory |
factory
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 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.collection.AbstractCollectionDecorator |
add, addAll, clear, contains, containsAll, equals, getCollection, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString |
Methods inherited from interface java.util.List |
add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray |
factory
protected final Factory factory
- The factory to use to lazily instantiate the objects
LazyList
protected LazyList(List list,
Factory factory)
- Constructor that wraps (not copies).
- Parameters:
list
- the list to decorate, must not be nullfactory
- the factory to use for creation, must not be null- Throws:
IllegalArgumentException
- if list or factory is null
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 nullfactory
- 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.
- Overrides:
get
in class AbstractListDecorator
- Parameters:
index
- the index to retrieve
subList
public List subList(int fromIndex,
int toIndex)
- Overrides:
subList
in class AbstractListDecorator
Copyright © 2001-2004 Apache Software Foundation. All Rights Reserved.