Class ListOrderedSet<E>

Type Parameters:
E - the type of the elements in this set
All Implemented Interfaces:
Serializable, Iterable<E>, Collection<E>, Set<E>

public class ListOrderedSet<E> extends AbstractSerializableSetDecorator<E>
Decorates another Set to ensure that the order of addition is retained and used by the iterator.

If an object is added to the set for a second time, it will remain in the original position in the iteration. The order can be observed from the set via the iterator or toArray methods.

The ListOrderedSet also has various useful direct methods. These include many from List, such as get(int), remove(int) and indexOf(int). An unmodifiable List view of the set can be obtained via asList().

This class cannot implement the List interface directly as various interface methods (notably equals/hashCode) are incompatible with a set.

This class is Serializable from Commons Collections 3.1.

Since:
3.0
See Also:
  • Field Details

    • serialVersionUID

      private static final long serialVersionUID
      Serialization version
      See Also:
    • setOrder

      private final List<E> setOrder
      Internal list to hold the sequence of objects
  • Constructor Details

    • ListOrderedSet

      public ListOrderedSet()
      Constructs a new empty ListOrderedSet using a HashSet and an ArrayList internally.
      Since:
      3.1
    • ListOrderedSet

      protected ListOrderedSet(Set<E> set)
      Constructor that wraps (not copies).
      Parameters:
      set - the set to decorate, must not be null
      Throws:
      IllegalArgumentException - if set is null
    • ListOrderedSet

      protected ListOrderedSet(Set<E> set, List<E> list)
      Constructor that wraps (not copies) the Set and specifies the list 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 Details

    • listOrderedSet

      public static <E> ListOrderedSet<E> listOrderedSet(Set<E> set, List<E> list)
      Factory method to create an ordered set specifying the list and set to use.

      The list and set must both be empty.

      Type Parameters:
      E - the element type
      Parameters:
      set - the set to decorate, must be empty and not null
      list - the list to decorate, must be empty and not null
      Returns:
      a new ordered set
      Throws:
      NullPointerException - if set or list is null
      IllegalArgumentException - if either the set or list is not empty
      Since:
      4.0
    • listOrderedSet

      public static <E> ListOrderedSet<E> listOrderedSet(Set<E> set)
      Factory method to create an ordered set.

      An ArrayList is used to retain order.

      Type Parameters:
      E - the element type
      Parameters:
      set - the set to decorate, must not be null
      Returns:
      a new ordered set
      Throws:
      NullPointerException - if set is null
      Since:
      4.0
    • listOrderedSet

      public static <E> ListOrderedSet<E> listOrderedSet(List<E> list)
      Factory method to create an ordered set using the supplied list to retain order.

      A HashSet is used for the set behaviour.

      NOTE: If the list contains duplicates, the duplicates are removed, altering the specified list.

      Type Parameters:
      E - the element type
      Parameters:
      list - the list to decorate, must not be null
      Returns:
      a new ordered set
      Throws:
      NullPointerException - if list is null
      Since:
      4.0
    • asList

      public List<E> asList()
      Gets an unmodifiable view of the order of the Set.
      Returns:
      an unmodifiable list view
    • clear

      public void clear()
      Specified by:
      clear in interface Collection<E>
      Specified by:
      clear in interface Set<E>
      Overrides:
      clear in class AbstractCollectionDecorator<E>
    • iterator

      public OrderedIterator<E> iterator()
      Specified by:
      iterator in interface Collection<E>
      Specified by:
      iterator in interface Iterable<E>
      Specified by:
      iterator in interface Set<E>
      Overrides:
      iterator in class AbstractCollectionDecorator<E>
    • add

      public boolean add(E object)
      Specified by:
      add in interface Collection<E>
      Specified by:
      add in interface Set<E>
      Overrides:
      add in class AbstractCollectionDecorator<E>
    • addAll

      public boolean addAll(Collection<? extends E> coll)
      Specified by:
      addAll in interface Collection<E>
      Specified by:
      addAll in interface Set<E>
      Overrides:
      addAll in class AbstractCollectionDecorator<E>
    • remove

      public boolean remove(Object object)
      Specified by:
      remove in interface Collection<E>
      Specified by:
      remove in interface Set<E>
      Overrides:
      remove 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
    • removeAll

      public boolean removeAll(Collection<?> coll)
      Specified by:
      removeAll in interface Collection<E>
      Specified by:
      removeAll in interface Set<E>
      Overrides:
      removeAll in class AbstractCollectionDecorator<E>
    • retainAll

      public boolean retainAll(Collection<?> coll)

      This implementation iterates over the elements of this set, checking each element in turn to see if it's contained in coll. If it's not contained, it's removed from this set. 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 Set<E>
      Overrides:
      retainAll in class AbstractCollectionDecorator<E>
    • toArray

      public Object[] toArray()
      Specified by:
      toArray in interface Collection<E>
      Specified by:
      toArray in interface Set<E>
      Overrides:
      toArray in class AbstractCollectionDecorator<E>
    • toArray

      public <T> T[] toArray(T[] a)
      Specified by:
      toArray in interface Collection<E>
      Specified by:
      toArray in interface Set<E>
      Overrides:
      toArray in class AbstractCollectionDecorator<E>
    • get

      public E get(int index)
      Returns the element at the specified position in this ordered set.
      Parameters:
      index - the position of the element in the ordered Set.
      Returns:
      the element at position index
      See Also:
    • indexOf

      public int indexOf(Object object)
      Returns the index of the first occurrence of the specified element in ordered set.
      Parameters:
      object - the element to search for
      Returns:
      the index of the first occurrence of the object, or -1 if this ordered set does not contain this object
      See Also:
    • add

      public void add(int index, E object)
      Inserts the specified element at the specified position if it is not yet contained in this ordered set (optional operation). Shifts the element currently at this position and any subsequent elements to the right.
      Parameters:
      index - the index at which the element is to be inserted
      object - the element to be inserted
      See Also:
    • addAll

      public boolean addAll(int index, Collection<? extends E> coll)
      Inserts all elements in the specified collection not yet contained in the ordered set at the specified position (optional operation). Shifts the element currently at the position and all subsequent elements to the right.
      Parameters:
      index - the position to insert the elements
      coll - the collection containing the elements to be inserted
      Returns:
      true if this ordered set changed as a result of the call
      See Also:
    • remove

      public E remove(int index)
      Removes the element at the specified position from the ordered set. Shifts any subsequent elements to the left.
      Parameters:
      index - the index of the element to be removed
      Returns:
      the element that has been remove from the ordered set
      See Also:
    • toString

      public String toString()
      Uses the underlying List's toString so that order is achieved. This means that the decorated Set's toString is not used, so any custom toStrings will be ignored.
      Overrides:
      toString in class AbstractCollectionDecorator<E>
      Returns:
      a string representation of the ordered set