org.apache.commons.collections4.list
Class LazyList<E>

java.lang.Object
  extended by org.apache.commons.collections4.collection.AbstractCollectionDecorator<E>
      extended by org.apache.commons.collections4.list.AbstractListDecorator<E>
          extended by org.apache.commons.collections4.list.AbstractSerializableListDecorator<E>
              extended by org.apache.commons.collections4.list.LazyList<E>
All Implemented Interfaces:
Serializable, Iterable<E>, Collection<E>, List<E>

public class LazyList<E>
extends AbstractSerializableListDecorator<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.

Since:
3.0
Version:
$Id: LazyList.java 1479405 2013-05-05 21:58:52Z tn $
See Also:
GrowthList, Serialized Form

Constructor 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
<E> LazyList<E>
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
add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray
 

Constructor Detail

LazyList

protected LazyList(List<E> list,
                   Factory<? extends E> factory)
Constructor that wraps (not copies).

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
Method Detail

lazyList

public static <E> LazyList<E> lazyList(List<E> list,
                                       Factory<? extends E> factory)
Factory method to create a lazily instantiating list.

Type Parameters:
E - the type of the elements in the list
Parameters:
list - the list to decorate, must not be null
factory - the factory to use for creation, must not be null
Returns:
a new lazy list
Throws:
IllegalArgumentException - if list or factory is null
Since:
4.0

get

public E 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 List<E>
Overrides:
get in class AbstractListDecorator<E>
Parameters:
index - the index to retrieve
Returns:
the element at the given index

subList

public List<E> subList(int fromIndex,
                       int toIndex)
Specified by:
subList in interface List<E>
Overrides:
subList in class AbstractListDecorator<E>


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