Interface SequencedCollection<E>

Type Parameters:: E - the type of elements in this collection

All Superinterfaces:: Collection<E>, Iterable<E>

All Known Subinterfaces:: BlockingDeque<E>, Deque<E>, List<E>, NavigableSet<E>, SequencedSet<E>, SortedSet<E>

All Known Implementing Classes:: AbstractList, AbstractSequentialList, ArrayDeque, ArrayList, AttributeList, ConcurrentLinkedDeque, ConcurrentSkipListSet, CopyOnWriteArrayList, LinkedBlockingDeque, LinkedHashSet, LinkedList, RoleList, RoleUnresolvedList, Stack, TreeSet, Vector

public interface SequencedCollection<E> extends Collection<E>

A collection that has a well-defined encounter order, that supports operations at both ends, and that is reversible. The elements of a sequenced collection have an encounter order, where conceptually the elements have a linear arrangement from the first element to the last element. Given any two elements, one element is either before (closer to the first element) or after (closer to the last element) the other element.

(Note that this definition does not imply anything about physical positioning of elements, such as their locations in a computer's memory.)

Several methods inherited from the Collection interface are required to operate on elements according to this collection's encounter order. For instance, the iterator method provides elements starting from the first element, proceeding through successive elements, until the last element. Other methods that are required to operate on elements in encounter order include the following: forEach, parallelStream, spliterator, stream, and all overloads of the toArray method.

This interface provides methods to add, retrieve, and remove elements at either end of the collection.

This interface also defines the reversed method, which provides a reverse-ordered view of this collection. In the reverse-ordered view, the concepts of first and last are inverted, as are the concepts of successor and predecessor. The first element of this collection is the last element of the reverse-ordered view, and vice-versa. The successor of some element in this collection is its predecessor in the reversed view, and vice-versa. All methods that respect the encounter order of the collection operate as if the encounter order is inverted. For instance, the Collection.iterator() method of the reversed view reports the elements in order from the last element of this collection to the first. The availability of the reversed method, and its impact on the ordering semantics of all applicable methods, allow convenient iteration, searching, copying, and streaming of the elements of this collection in either forward order or reverse order.

This class is a member of the Java Collections Framework.

API Note:: This interface does not impose any requirements on the equals and hashCode methods, because requirements imposed by sub-interfaces List and SequencedSet (which inherits requirements from Set) would be in conflict. See the specifications for Collection.equals and Collection.hashCode for further information.
Since:: 21

Method Summary

Modifier and Type	Method	Description
`default void`	`addFirst(E e)`	Adds an element as the first element of this collection (optional operation).
`default void`	`addLast(E e)`	Adds an element as the last element of this collection (optional operation).
`default E`	`getFirst()`	Gets the first element of this collection.
`default E`	`getLast()`	Gets the last element of this collection.
`default E`	`removeFirst()`	Removes and returns the first element of this collection (optional operation).
`default E`	`removeLast()`	Removes and returns the last element of this collection (optional operation).
`SequencedCollection<E>`	`reversed()`	Returns a reverse-ordered view of this collection.

Methods declared in interface Collection

add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, parallelStream, remove, removeAll, removeIf, retainAll, size, spliterator, stream, toArray, toArray, toArray

Modifier and Type	Method	Description
`boolean`	`add(E e)`	Ensures that this collection contains the specified element (optional operation).
`boolean`	`addAll(Collection<? extends E> c)`	Adds all of the elements in the specified collection to this collection (optional operation).
`void`	`clear()`	Removes all of the elements from this collection (optional operation).
`boolean`	`contains(Object o)`	Returns `true` if this collection contains the specified element.
`boolean`	`containsAll(Collection<?> c)`	Returns `true` if this collection contains all of the elements in the specified collection.
`boolean`	`equals(Object o)`	Compares the specified object with this collection for equality.
`int`	`hashCode()`	Returns the hash code value for this collection.
`boolean`	`isEmpty()`	Returns `true` if this collection contains no elements.
`Iterator<E>`	`iterator()`	Returns an iterator over the elements in this collection.
`default Stream<E>`	`parallelStream()`	Returns a possibly parallel `Stream` with this collection as its source.
`boolean`	`remove(Object o)`	Removes a single instance of the specified element from this collection, if it is present (optional operation).
`boolean`	`removeAll(Collection<?> c)`	Removes all of this collection's elements that are also contained in the specified collection (optional operation).
`default boolean`	`removeIf(Predicate<? super E> filter)`	Removes all of the elements of this collection that satisfy the given predicate (optional operation).
`boolean`	`retainAll(Collection<?> c)`	Retains only the elements in this collection that are contained in the specified collection (optional operation).
`int`	`size()`	Returns the number of elements in this collection.
`default Spliterator<E>`	`spliterator()`	Creates a `Spliterator` over the elements in this collection.
`default Stream<E>`	`stream()`	Returns a sequential `Stream` with this collection as its source.
`Object[]`	`toArray()`	Returns an array containing all of the elements in this collection.
`default <T> T[]`	`toArray(IntFunction<T[]> generator)`	Returns an array containing all of the elements in this collection, using the provided `generator` function to allocate the returned array.
`<T> T[]`	`toArray(T[] a)`	Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.

Methods declared in interface Iterable

forEach

Modifier and Type	Method	Description
`default void`	`forEach(Consumer<? super E> action)`	Performs the given action for each element of the `Iterable` until all elements have been processed or the action throws an exception.

Method Details

reversed

SequencedCollection<E> reversed()

Returns a reverse-ordered view of this collection. The encounter order of elements in the returned view is the inverse of the encounter order of elements in this collection. The reverse ordering affects all order-sensitive operations, including those on the view collections of the returned view. If the collection implementation permits modifications to this view, the modifications "write through" to the underlying collection. Changes to the underlying collection might or might not be visible in this reversed view, depending upon the implementation.

Returns:: a reverse-ordered view of this collection

addFirst

default void addFirst(E e)

Adds an element as the first element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the first element in encounter order.

Implementation Requirements:: The implementation in this interface always throws UnsupportedOperationException.
Parameters:: e - the element to be added
Throws:: NullPointerException - if the specified element is null and this collection does not permit null elements; UnsupportedOperationException - if this collection implementation does not support this operation

addLast

default void addLast(E e)

Adds an element as the last element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the last element in encounter order.

Implementation Requirements:: The implementation in this interface always throws UnsupportedOperationException.
Parameters:: e - the element to be added.
Throws:: NullPointerException - if the specified element is null and this collection does not permit null elements; UnsupportedOperationException - if this collection implementation does not support this operation

getFirst

default E getFirst()

Gets the first element of this collection.

Implementation Requirements:: The implementation in this interface obtains an iterator of this collection, and then it obtains an element by calling the iterator's next method. Any NoSuchElementException thrown is propagated. Otherwise, it returns the element.
Returns:: the retrieved element
Throws:: NoSuchElementException - if this collection is empty

getLast

default E getLast()

Gets the last element of this collection.

Implementation Requirements:: The implementation in this interface obtains an iterator of the reversed view of this collection, and then it obtains an element by calling the iterator's next method. Any NoSuchElementException thrown is propagated. Otherwise, it returns the element.
Returns:: the retrieved element
Throws:: NoSuchElementException - if this collection is empty

removeFirst

default E removeFirst()

Removes and returns the first element of this collection (optional operation).

Implementation Requirements:: The implementation in this interface obtains an iterator of this collection, and then it obtains an element by calling the iterator's next method. Any NoSuchElementException thrown is propagated. It then calls the iterator's remove method. Any UnsupportedOperationException thrown is propagated. Then, it returns the element.
Returns:: the removed element
Throws:: NoSuchElementException - if this collection is empty; UnsupportedOperationException - if this collection implementation does not support this operation

removeLast

default E removeLast()

Removes and returns the last element of this collection (optional operation).

Implementation Requirements:: The implementation in this interface obtains an iterator of the reversed view of this collection, and then it obtains an element by calling the iterator's next method. Any NoSuchElementException thrown is propagated. It then calls the iterator's remove method. Any UnsupportedOperationException thrown is propagated. Then, it returns the element.
Returns:: the removed element
Throws:: NoSuchElementException - if this collection is empty; UnsupportedOperationException - if this collection implementation does not support this operation

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