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org.apache.commons.collections.list

Class SetUniqueList

java.lang.Object
|
+--org.apache.commons.collections.collection.AbstractCollectionDecorator
   |
   +--org.apache.commons.collections.list.AbstractListDecorator
      |
      +--org.apache.commons.collections.list.SetUniqueList


public class SetUniqueList
extends AbstractListDecorator

Decorates a List to ensure that no duplicates are present much like a Set.

The List interface makes certain assumptions/requirements. This implementation breaks these in certain ways, but this is merely the result of rejecting duplicates. Each violation is explained in the method, but it should not affect you.

The org.apache.commons.collections.set.ListOrderedSet ListOrderedSet class provides an alternative approach, by wrapping an existing Set and retaining insertion order in the iterator.

Since:
Commons Collections 3.0
Authors:
Matthew Hawthorne
Stephen Colebourne

Field Summary

Set

set

Internal Set to maintain uniqueness.

Constructor Summary

SetUniqueList(List list, Set set)

Constructor that wraps (not copies) the List and specifies the set to use.

Method Summary

boolean

add(Object object)

Adds an element to the list if it is not already present.

void

add(int index, Object object)

Adds an element to a specific index in the list if it is not already present.

boolean

addAll(Collection coll)

Adds an element to the end of the list if it is not already present.

boolean

addAll(int index, Collection coll)

Adds a collection of objects to the end of the list avoiding duplicates.

Set

asSet()

Gets an unmodifiable view as a Set.

void

clear()

boolean

contains(Object object)

boolean

containsAll(Collection coll)

static SetUniqueList

decorate(List list)

Factory method to create a SetList using the supplied list to retain order.

Iterator

iterator()

ListIterator

listIterator()

ListIterator

listIterator(int index)

boolean

remove(Object object)

Object

remove(int index)

boolean

removeAll(Collection coll)

boolean

retainAll(Collection coll)

Object

set(int index, Object object)

Sets the value at the specified index avoiding duplicates.

List

subList(int fromIndex, int toIndex)

Field Details

set

protected final Set set

Internal Set to maintain uniqueness.

Constructor Details

SetUniqueList

protected SetUniqueList(List list, Set set)

Constructor that wraps (not copies) the List and specifies the set to use.

The set and list must both be correctly initialised to the same elements.

Parameters:
list - the set to decorate, must not be null
set - the list to decorate, must not be null
Throws:
- if set or list is null

Method Details

add

public void add(int index, Object object)

Adds an element to a specific index in the list if it is not already present.

(Violation) The List interface makes the assumption that the element is always inserted. This may not happen with this implementation.

Parameters:
index - the index to insert at
object - the object to add

add

public boolean add(Object object)

Adds an element to the list if it is not already present.

(Violation) The List interface requires that this method returns true always. However this class may return false because of the Set behaviour.

Parameters:
object - the object to add
Returns:
true if object was added

addAll

public boolean addAll(Collection coll)

Adds an element to the end of the list if it is not already present.

(Violation) The List interface makes the assumption that the element is always inserted. This may not happen with this implementation.

Parameters:
coll - the collection to add

addAll

public boolean addAll(int index, Collection coll)

Adds a collection of objects to the end of the list avoiding duplicates.

Only elements that are not already in this list will be added, and duplicates from the specified collection will be ignored.

(Violation) The List interface makes the assumption that the elements are always inserted. This may not happen with this implementation.

Parameters:
index - the index to insert at
coll - the collection to add in iterator order
Returns:
true if this collection changed

asSet

public Set asSet()

Gets an unmodifiable view as a Set.

Returns:
an unmodifiable set view

clear

public void clear()


contains

public boolean contains(Object object)

Parameters:
object

containsAll

public boolean containsAll(Collection coll)

Parameters:
coll

decorate

public static SetUniqueList decorate(List list)

Factory method to create a SetList using the supplied list to retain order.

If the list contains duplicates, these are removed (first indexed one kept). A HashSet is used for the set behaviour.

Parameters:
list - the list to decorate, must not be null
Throws:
- if list is null

iterator

public Iterator iterator()


listIterator

public ListIterator listIterator()


listIterator

public ListIterator listIterator(int index)

Parameters:
index

remove

public Object remove(int index)

Parameters:
index

remove

public boolean remove(Object object)

Parameters:
object

removeAll

public boolean removeAll(Collection coll)

Parameters:
coll

retainAll

public boolean retainAll(Collection coll)

Parameters:
coll

set

public Object set(int index, Object object)

Sets the value at the specified index avoiding duplicates.

The object is set into the specified index. Afterwards, any previous duplicate is removed If the object is not already in the list then a normal set occurs. If it is present, then the old version is removed and re-added at this index

Parameters:
index - the index to insert at
object - the object to set
Returns:
the previous object

subList

public List subList(int fromIndex, int toIndex)

Parameters:
fromIndex
toIndex