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
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
.
- Commons Collections 3.0
- Stephen Colebourne
- Arron Bates
- Paul Jack
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).
- list - the list to decorate, must not be null
- factory - the factory to use for creation, must not be null
- if list or factory is null
decorate
public static List decorate(List list, Factory factory)
Factory method to create a lazily instantiating list.
- list - the list to decorate, must not be null
- factory - the factory to use for creation, must not be null
- 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.
- index - the index to retrieve
subList
public List subList(int fromIndex, int toIndex)
- fromIndex
- toIndex
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: After the above code is executed,obj
will contain a newDate
instance. Furthermore, thatDate
instance is the fourth element in the list. The first, second, and third element are all set tonull
.