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>

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

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `add(E object)` Adds an element to the list if it is not already present.
    `void` | `add(int index, E object)` Adds an element to a specific index in the list if it is not already present.
    `boolean` | `addAll(Collection<? extends E> coll)` Adds a collection of objects to the end of the list avoiding duplicates.
    `boolean` | `addAll(int index, Collection<? extends E> coll)` Adds a collection of objects a specific index in 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` | `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.List

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

    - ### Methods inherited from interface java.util.Collection

      `parallelStream, removeIf, stream`

    - ### Methods inherited from interface java.lang.Iterable

      `forEach`

- - ### Constructor Detail

    - #### 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 initialised to the same elements.

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

  - ### Method Detail

    - #### 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 behaviour.

      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

    - #### asSet

          public Set<E> asSet()

      Gets an unmodifiable view as a Set.
      Returns:
        an unmodifiable set view

    - #### 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` behaviour.

      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

    - #### 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

    - #### 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>`

    - #### remove

          public E remove(int index)

      Specified by:
        `remove` in interface `List<E>`
      Overrides:
        `remove` in class `AbstractListDecorator<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>`

    - #### 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>`

    - #### 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>`

    - #### iterator

          public Iterator<E> iterator()

      Specified by:
        `iterator` in interface `Iterable<E>`
      Specified by:
        `iterator` in interface `Collection<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>`

    - #### 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>`

    - #### 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`

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