By default, if no container class is specified for a particular queue class instantiation, the standard container deque is used. The standard container classes deque and list fulfill these requirements. This underlying container shall support at least the following operations: The underlying container may be one of the standard container class template or some other specifically designed container class. Elements are pushed into the "back" of the specific container and popped from its "front". Queues are implemented as containers adaptors, which are classes that use an encapsulated object of a specific container class as its underlying container, providing a specific set of member functions to access its elements. The associated exception is thrown.FIFO queue queues are a type of container adaptor, specifically designed to operate in a FIFO context (first-in first-out), where elements are inserted into one end of the container and extracted from the other. In only some of the elements having been successfully added when To call offer separately on each element.Īn exception encountered while trying to add an element may result When using a capacity-restricted deque, it is generally preferable In the order that they are returned by the collection's iterator. Of this deque, as if by calling addLast(E) on each one, Prevents it from being added to this deque NullPointerException - if the specified element is null and thisĭeque does not permit null elements IllegalArgumentException - if some property of the specifiedĮlement prevents it from being added to this dequeĪdds all of the elements in the specified collection at the end Time due to capacity restrictions ClassCastException - if the class of the specified element Specified by: add in interface Collection Specified by: add in interface Queue Parameters: e - the element to add Returns: true (as specified by Collection.add(E)) Throws: IllegalStateException - if the element cannot be added at this When using a capacity-restricted deque, it is generally preferable to IllegalStateException if no space is currently available. Immediately without violating capacity restrictions, returning (in other words, at the tail of this deque) if it is possible to do so Inserts the specified element into the queue represented by this deque Methods, but instead inherit the identity-based versions from class Null is used as a special return value by various methodsĭeque implementations generally do not defineĮlement-based versions of the equals and hashCode Take advantage of the ability to insert nulls. That do allow null elements are strongly encouraged not to To prohibit the insertion of null elements, they are stronglyĮncouraged to do so. While Deque implementations are not strictly required Provide support for indexed access to elements. Unlike the List interface, this interface does not This interface provides two methods to remove interior Note that the peek method works equally well whenĪ deque is used as a queue or a stack in either case, elements are Stack methods are equivalent to DequeĬomparison of Stack and Deque methods Stack Method When a deque is used as a stack, elements are pushed and popped from theīeginning of the deque. Interface should be used in preference to the legacy Stack class. Inherited from the Queue interface are precisely equivalent toĭeque methods as indicated in the following table:Ĭomparison of Queue and Deque methods Queue Methodĭeques can also be used as LIFO (Last-In-First-Out) stacks. Elements areĪdded at the end of the deque and removed from the beginning. Used as a queue, FIFO (First-In-First-Out) behavior results. This interface extends the Queue interface. The twelve methods described above are summarized in the The latter form of the insert operation isĭesigned specifically for use with capacity-restrictedĭeque implementations in most implementations, insert Special value (either null or false, depending on One throws an exception if the operation fails, the other returns a Each of these methods exists in two forms: Methods are provided to insert, remove, andĮxamine the element. This interface defines methods to access the elements at bothĮnds of the deque. They may contain, but this interface supports capacity-restrictedĭeques as well as those with no fixed size limit. Implementations place no fixed limits on the number of elements The name deque is short for "double ended queue"Īnd is usually pronounced "deck". A linear collection that supports element insertion and removal atīoth ends.
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