A linear collection that supports element insertion and removal at both ends. The name deque
is short for "double ended queue" and is usually pronounced "deck". Most
implementations place no fixed limits on the number of elements they may contain, but this interface supports capacity-restricted deques as well as those with no fixed size limit.
This interface defines methods to access the elements at both ends of the deque. Methods are provided to insert, remove, and examine the element. Each of these methods exists in two forms: one throws an exception if the operation fails, the other returns a special value (either
false, depending on the operation). The latter form of the insert operation is designed specifically for use with capacity-restricted
Deque implementations; in most implementations, insert operations cannot fail.
The twelve methods described above are summarized in the following table:
This interface extends the
Queue interface. When a deque is used as a queue, FIFO (First-In-First-Out) behavior results. Elements are added at the end of the deque and removed from the beginning. The methods inherited from the
Queue interface are precisely equivalent to
Deque methods as indicated in the following table:
Deques can also be used as LIFO (Last-In-First-Out) stacks. This interface should be used in preference to the legacy
Stack class. When a deque is used as a stack, elements are pushed and popped from the beginning of the deque. Stack methods are precisely equivalent to
Deque methods as indicated in the table below:
Note that the
peek method works equally well when a deque is used as a queue or a stack; in either case, elements are drawn from the beginning of the deque.
This interface provides two methods to remove interior elements,
List interface, this interface does not provide support for indexed access to elements.
Deque implementations are not strictly required to prohibit the insertion of null elements, they are strongly encouraged to do so. Users of any
Deque implementations that do allow null elements are strongly encouraged not to take advantage of the ability to insert nulls. This is so because
null is used as a special return value by various methods to indicate that the deque is empty.
Deque implementations generally do not define element-based versions of the
hashCode methods, but instead inherit the identity-based versions from class
This interface is a member of the Java Collections Framework .