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.AbstractSerializableListDecorator

org.apache.commons.collections.list.LazyList

All Implemented Interfaces:

java.io.Serializable, java.lang.Iterable, java.util.Collection, java.util.List

public class LazyList
extends AbstractSerializableListDecorator

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.

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

See Also:

GrowthList, Serialized Form

Method Summary

Modifier and Type	Method and Description
static java.util.List	decorate(java.util.List list, Factory factory) Factory method to create a lazily instantiating list.
java.lang.Object	get(int index) Decorate the get method to perform the lazy behaviour.
java.util.List	subList(int fromIndex, int toIndex)

Methods inherited from class org.apache.commons.collections.list.AbstractListDecorator

add, addAll, indexOf, lastIndexOf, listIterator, listIterator, remove, set

Methods inherited from class org.apache.commons.collections.collection.AbstractCollectionDecorator

add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.List

add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, replaceAll, retainAll, size, sort, spliterator, toArray, toArray

Methods inherited from interface java.util.Collection

parallelStream, removeIf, stream

Methods inherited from interface java.lang.Iterable

forEach

Method Detail

decorate

public static java.util.List decorate(java.util.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:

java.lang.IllegalArgumentException - if list or factory is null

get

public java.lang.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.

Specified by:

get in interface java.util.List

Overrides:

get in class AbstractListDecorator

Parameters:

index - the index to retrieve

subList

public java.util.List subList(int fromIndex,
                              int toIndex)

Specified by:

subList in interface java.util.List

Overrides:

subList in class AbstractListDecorator