Package org.apache.commons.collections4.list

Class SetUniqueList<E>

java.lang.Object

org.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.SetUniqueList<E>

Type Parameters:

E - the type of the elements in the list.

All Implemented Interfaces:

Serializable, Iterable<E>, Collection<E>, List<E>

public class SetUniqueList<E>
extends AbstractSerializableListDecorator<E>

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. Bear in mind that Sets require immutable objects to function correctly.

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

This class is Serializable from Commons Collections 3.1.

Since:

3.0

See Also:

• Serialized Form

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	SetUniqueList(List<E> list, Set<E> set)	Constructor that wraps (not copies) the List and specifies the set to use.

Method Summary

Modifier and Type	Method	Description
void	add(int index, E object)	Adds an element to a specific index in the list if it is not already present.
boolean	add(E object)	Adds an element to the list if it is not already present.
boolean	addAll(int index, Collection<? extends E> coll)	Adds a collection of objects a specific index in the list avoiding duplicates.
boolean	addAll(Collection<? extends E> coll)	Adds a collection of objects to the end of the list avoiding duplicates.
Set<E>	asSet()	Gets an unmodifiable view as a Set.
void	clear()
boolean	contains(Object object)
boolean	containsAll(Collection<?> coll)
protected Set<E>	createSetBasedOnList(Set<E> set, List<E> list)	Create a new Set with the same type as the provided set and populate it with all elements of list.
Iterator<E>	iterator()
ListIterator<E>	listIterator()
ListIterator<E>	listIterator(int index)
E	remove(int index)
boolean	remove(Object object)
boolean	removeAll(Collection<?> coll)
boolean	removeIf(Predicate<? super E> filter)
boolean	retainAll(Collection<?> coll)
E	set(int index, E object)	Sets the value at the specified index avoiding duplicates.
static <E> SetUniqueList<E>	setUniqueList(List<E> list)	Factory method to create a SetList using the supplied list to retain order.
List<E>	subList(int fromIndex, int toIndex)

Methods inherited from class org.apache.commons.collections4.list.AbstractListDecorator

decorated, equals, get, hashCode, indexOf, lastIndexOf

Methods inherited from class org.apache.commons.collections4.collection.AbstractCollectionDecorator

isEmpty, 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.Collection

parallelStream, stream

Methods inherited from interface java.lang.Iterable

forEach

Methods inherited from interface java.util.List

isEmpty, replaceAll, size, sort, spliterator, toArray, toArray

Constructor Details

SetUniqueList

protected SetUniqueList(List<E> list,
 Set<E> set)

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

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

Parameters:

list - the list to decorate, must not be null

set - the set to decorate, must not be null

Throws:

NullPointerException - if set or list is null

Method Details

setUniqueList

public static <E> SetUniqueList<E> setUniqueList(List<E> 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 behavior.

Type Parameters:

E - the element type

Parameters:

list - the list to decorate, must not be null

Returns:

a new SetUniqueList

Throws:

NullPointerException - if list is null

Since:

4.0

add

public boolean add(E 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 behavior.

Specified by:

add in interface Collection<E>

Specified by:

add in interface List<E>

Overrides:

add in class AbstractCollectionDecorator<E>

Parameters:

object - the object to add

Returns:

true if object was added

add

public void add(int index,
 E 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.

Specified by:

add in interface List<E>

Overrides:

add in class AbstractListDecorator<E>

Parameters:

index - the index to insert at

object - the object to add

addAll

public boolean addAll(Collection<? extends E> 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.

Specified by:

addAll in interface Collection<E>

Specified by:

addAll in interface List<E>

Overrides:

addAll in class AbstractCollectionDecorator<E>

Parameters:

coll - the collection to add in iterator order

Returns:

true if this collection changed

addAll

public boolean addAll(int index,
 Collection<? extends E> coll)

Adds a collection of objects a specific index in 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.

Specified by:

addAll in interface List<E>

Overrides:

addAll in class AbstractListDecorator<E>

Parameters:

index - the index to insert at

coll - the collection to add in iterator order

Returns:

true if this collection changed

asSet

public Set<E> asSet()

Gets an unmodifiable view as a Set.

Returns:

an unmodifiable set view

clear

public void clear()

Specified by:

clear in interface Collection<E>

Specified by:

clear in interface List<E>

Overrides:

clear in class AbstractCollectionDecorator<E>

contains

public boolean contains(Object object)

Specified by:

contains in interface Collection<E>

Specified by:

contains in interface List<E>

Overrides:

contains in class AbstractCollectionDecorator<E>

containsAll

public boolean containsAll(Collection<?> coll)

Specified by:

containsAll in interface Collection<E>

Specified by:

containsAll in interface List<E>

Overrides:

containsAll in class AbstractCollectionDecorator<E>

createSetBasedOnList

protected Set<E> createSetBasedOnList(Set<E> set,
 List<E> list)

Create a new Set with the same type as the provided set and populate it with all elements of list.

Parameters:

set - the Set to be used as return type, must not be null

list - the List to populate the Set

Returns:

a new Set populated with all elements of the provided List

iterator

public Iterator<E> iterator()

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface List<E>

Overrides:

iterator in class AbstractCollectionDecorator<E>

listIterator

public ListIterator<E> listIterator()

Specified by:

listIterator in interface List<E>

Overrides:

listIterator in class AbstractListDecorator<E>

listIterator

public ListIterator<E> listIterator(int index)

Specified by:

listIterator in interface List<E>

Overrides:

listIterator in class AbstractListDecorator<E>

remove

public E remove(int index)

Specified by:

remove in interface List<E>

Overrides:

remove in class AbstractListDecorator<E>

remove

public boolean remove(Object object)

Specified by:

remove in interface Collection<E>

Specified by:

remove in interface List<E>

Overrides:

remove in class AbstractCollectionDecorator<E>

removeAll

public boolean removeAll(Collection<?> coll)

Specified by:

removeAll in interface Collection<E>

Specified by:

removeAll in interface List<E>

Overrides:

removeAll in class AbstractCollectionDecorator<E>

removeIf

public boolean removeIf(Predicate<? super E> filter)

Specified by:

removeIf in interface Collection<E>

Overrides:

removeIf in class AbstractCollectionDecorator<E>

Since:

4.4

retainAll

public boolean retainAll(Collection<?> coll)

This implementation iterates over the elements of this list, checking each element in turn to see if it's contained in coll. If it's not contained, it's removed from this list. As a consequence, it is advised to use a collection type for coll that provides a fast (e.g. O(1)) implementation of Collection.contains(Object).

Specified by:

retainAll in interface Collection<E>

Specified by:

retainAll in interface List<E>

Overrides:

retainAll in class AbstractCollectionDecorator<E>

set

public E set(int index,
 E 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.

Specified by:

set in interface List<E>

Overrides:

set in class AbstractListDecorator<E>

Parameters:

index - the index to insert at

object - the object to set

Returns:

the previous object

subList

public List<E> subList(int fromIndex,
 int toIndex)

NOTE: from 4.0, an unmodifiable list will be returned, as changes to the subList can invalidate the parent list.

Specified by:

subList in interface List<E>

Overrides:

subList in class AbstractListDecorator<E>