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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.AbstractSerializableListDecorator
                  org.apache.commons.collections.list.SetUniqueList

All Implemented Interfaces:
  java.io.Serializable, java.lang.Iterable, java.util.Collection, java.util.List

    public class SetUniqueList

extends AbstractSerializableListDecorator

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:
  Commons Collections 3.0
Version:
  $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
Author:
  Matthew Hawthorne, Stephen Colebourne, Tom Dunham
See Also:
  Serialized Form

Field Summary
`protected java.util.Set` | `set` Internal Set to maintain uniqueness.

Fields inherited from class org.apache.commons.collections.collection.AbstractCollectionDecorator
`collection`

Constructor Summary
`protected` | `SetUniqueList(java.util.List list, java.util.Set set)` Constructor that wraps (not copies) the List and specifies the set to use.

Method Summary
`void` | `add(int index, java.lang.Object object)` Adds an element to a specific index in the list if it is not already present.
`boolean` | `add(java.lang.Object object)` Adds an element to the list if it is not already present.
`boolean` | `addAll(java.util.Collection coll)` Adds an element to the end of the list if it is not already present.
`boolean` | `addAll(int index, java.util.Collection coll)` Adds a collection of objects to the end of the list avoiding duplicates.
`java.util.Set` | `asSet()` Gets an unmodifiable view as a Set.
`void` | `clear()`
`boolean` | `contains(java.lang.Object object)`
`boolean` | `containsAll(java.util.Collection coll)`
`static SetUniqueList` | `decorate(java.util.List list)` Factory method to create a SetList using the supplied list to retain order.
`java.util.Iterator` | `iterator()`
`java.util.ListIterator` | `listIterator()`
`java.util.ListIterator` | `listIterator(int index)`
`java.lang.Object` | `remove(int index)`
`boolean` | `remove(java.lang.Object object)`
`boolean` | `removeAll(java.util.Collection coll)`
`boolean` | `retainAll(java.util.Collection coll)`
`java.lang.Object` | `set(int index, java.lang.Object object)` Sets the value at the specified index avoiding duplicates.
`java.util.List` | `subList(int fromIndex, int toIndex)`

Methods inherited from class org.apache.commons.collections.list.AbstractListDecorator
`get, getList, indexOf, lastIndexOf`

Methods inherited from class org.apache.commons.collections.collection.AbstractCollectionDecorator
`equals, getCollection, hashCode, isEmpty, 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
`equals, hashCode, isEmpty, size, toArray, toArray`

Field Detail

### set

    protected final java.util.Set set

  Internal Set to maintain uniqueness.

Constructor Detail

### SetUniqueList

    protected SetUniqueList(java.util.List list,
                            java.util.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:
    `set` - the set to decorate, must not be null
    `list` - the list to decorate, must not be null
  Throws:
    `java.lang.IllegalArgumentException` - if set or list is null

Method Detail

### decorate

    public static SetUniqueList decorate(java.util.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:
    `java.lang.IllegalArgumentException` - if list is null

### asSet

    public java.util.Set asSet()

  Gets an unmodifiable view as a Set.

  Returns:
    an unmodifiable set view

### add

    public boolean add(java.lang.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.

  Specified by:
    `add` in interface `java.util.Collection`
  Specified by:
    `add` in interface `java.util.List`
  Overrides:
    `add` in class `AbstractCollectionDecorator`
  Parameters:
    `object` - the object to add
  Returns:
    true if object was added

### add

    public void add(int index,
                    java.lang.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.

  Specified by:
    `add` in interface `java.util.List`
  Overrides:
    `add` in class `AbstractListDecorator`
  Parameters:
    `index` - the index to insert at
    `object` - the object to add

### addAll

    public boolean addAll(java.util.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.

  Specified by:
    `addAll` in interface `java.util.Collection`
  Specified by:
    `addAll` in interface `java.util.List`
  Overrides:
    `addAll` in class `AbstractCollectionDecorator`
  Parameters:
    `coll` - the collection to add

### addAll

    public boolean addAll(int index,
                          java.util.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.

  Specified by:
    `addAll` in interface `java.util.List`
  Overrides:
    `addAll` in class `AbstractListDecorator`
  Parameters:
    `index` - the index to insert at
    `coll` - the collection to add in iterator order
  Returns:
    true if this collection changed

### set

    public java.lang.Object set(int index,
                                java.lang.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.

  Specified by:
    `set` in interface `java.util.List`
  Overrides:
    `set` in class `AbstractListDecorator`
  Parameters:
    `index` - the index to insert at
    `object` - the object to set
  Returns:
    the previous object

### remove

    public boolean remove(java.lang.Object object)

  Specified by:
    `remove` in interface `java.util.Collection`
  Specified by:
    `remove` in interface `java.util.List`
  Overrides:
    `remove` in class `AbstractCollectionDecorator`

### remove

    public java.lang.Object remove(int index)

  Specified by:
    `remove` in interface `java.util.List`
  Overrides:
    `remove` in class `AbstractListDecorator`

### removeAll

    public boolean removeAll(java.util.Collection coll)

  Specified by:
    `removeAll` in interface `java.util.Collection`
  Specified by:
    `removeAll` in interface `java.util.List`
  Overrides:
    `removeAll` in class `AbstractCollectionDecorator`

### retainAll

    public boolean retainAll(java.util.Collection coll)

  Specified by:
    `retainAll` in interface `java.util.Collection`
  Specified by:
    `retainAll` in interface `java.util.List`
  Overrides:
    `retainAll` in class `AbstractCollectionDecorator`

### clear

    public void clear()

  Specified by:
    `clear` in interface `java.util.Collection`
  Specified by:
    `clear` in interface `java.util.List`
  Overrides:
    `clear` in class `AbstractCollectionDecorator`

### contains

    public boolean contains(java.lang.Object object)

  Specified by:
    `contains` in interface `java.util.Collection`
  Specified by:
    `contains` in interface `java.util.List`
  Overrides:
    `contains` in class `AbstractCollectionDecorator`

### containsAll

    public boolean containsAll(java.util.Collection coll)

  Specified by:
    `containsAll` in interface `java.util.Collection`
  Specified by:
    `containsAll` in interface `java.util.List`
  Overrides:
    `containsAll` in class `AbstractCollectionDecorator`

### iterator

    public java.util.Iterator iterator()

  Specified by:
    `iterator` in interface `java.lang.Iterable`
  Specified by:
    `iterator` in interface `java.util.Collection`
  Specified by:
    `iterator` in interface `java.util.List`
  Overrides:
    `iterator` in class `AbstractCollectionDecorator`

### listIterator

    public java.util.ListIterator listIterator()

  Specified by:
    `listIterator` in interface `java.util.List`
  Overrides:
    `listIterator` in class `AbstractListDecorator`

### listIterator

    public java.util.ListIterator listIterator(int index)

  Specified by:
    `listIterator` in interface `java.util.List`
  Overrides:
    `listIterator` in class `AbstractListDecorator`

### subList

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

  Specified by:
    `subList` in interface `java.util.List`
  Overrides:
    `subList` in class `AbstractListDecorator`

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