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java.lang.Objectorg.apache.commons.collections4.collection.AbstractCollectionDecorator<E>
org.apache.commons.collections4.list.AbstractListDecorator<E>
org.apache.commons.collections4.list.AbstractSerializableListDecorator<E>
org.apache.commons.collections4.list.LazyList<E>
public class LazyList<E>
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<Date> factory = new Factory<Date>() { public Date create() { return new Date(); } } List<Date> lazy = LazyList.decorate(new ArrayList<Date>(), factory); Date date = lazy.get(3);After the above code is executed,
date
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.
GrowthList
,
Serialized FormConstructor Summary | |
---|---|
protected |
LazyList(List<E> list,
Factory<? extends E> factory)
Constructor that wraps (not copies). |
Method Summary | ||
---|---|---|
E |
get(int index)
Decorate the get method to perform the lazy behaviour. |
|
static
|
lazyList(List<E> list,
Factory<? extends E> factory)
Factory method to create a lazily instantiating list. |
|
List<E> |
subList(int fromIndex,
int toIndex)
|
Methods inherited from class org.apache.commons.collections4.list.AbstractListDecorator |
---|
add, addAll, decorated, indexOf, lastIndexOf, listIterator, listIterator, remove, set |
Methods inherited from class org.apache.commons.collections4.collection.AbstractCollectionDecorator |
---|
add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, setCollection, size, toArray, toArray, toString |
Methods inherited from class java.lang.Object |
---|
clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
Methods inherited from interface java.util.List |
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add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray |
Constructor Detail |
---|
protected LazyList(List<E> list, Factory<? extends E> factory)
list
- the list to decorate, must not be nullfactory
- the factory to use for creation, must not be null
IllegalArgumentException
- if list or factory is nullMethod Detail |
---|
public static <E> LazyList<E> lazyList(List<E> list, Factory<? extends E> factory)
E
- the type of the elements in the listlist
- the list to decorate, must not be nullfactory
- the factory to use for creation, must not be null
IllegalArgumentException
- if list or factory is nullpublic E get(int index)
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.
get
in interface List<E>
get
in class AbstractListDecorator<E>
index
- the index to retrieve
public List<E> subList(int fromIndex, int toIndex)
subList
in interface List<E>
subList
in class AbstractListDecorator<E>
|
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