OpenJDK 27 · java.util.Deque · APIdia, the JavaDoc alternative

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 Deque 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 null or 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:

Summary of Deque methods
	Throws exception	Special value	Throws exception	Special value
	First Element (Head)		Last Element (Tail)
Insert	`addFirst(e)`	`offerFirst(e)`	`addLast(e)`	`offerLast(e)`
Remove	`removeFirst()`	`pollFirst()`	`removeLast()`	`pollLast()`
Examine	`getFirst()`	`peekFirst()`	`getLast()`	`peekLast()`

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:

Comparison of Queue and Deque methods
`Queue` Method	Equivalent `Deque` Method
`add(e)`	`addLast(e)`
`offer(e)`	`offerLast(e)`
`remove()`	`removeFirst()`
`poll()`	`pollFirst()`
`element()`	`getFirst()`
`peek()`	`peekFirst()`

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 equivalent to Deque methods as indicated in the table below:

Comparison of Stack and Deque methods
Stack Method	Equivalent `Deque` Method
`push(e)`	`addFirst(e)`
`pop()`	`removeFirst()`
`peek()`	`peekFirst()`

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, removeFirstOccurrence and removeLastOccurrence.

Unlike the List interface, this interface does not provide support for indexed access to elements.

While 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 equals and hashCode methods, but instead inherit the identity-based versions from class Object.

This interface is a member of the Java Collections Framework.

Method Summary

Modifier and Type	Method and Description
public boolean	Returns: `true` (as specified by `Collection#add`) add(E the element to add e) Redeclares java.util.Queue.add, java.util.Collection.add. Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and throwing an `IllegalStateException` if no space is currently available.
public boolean	Returns: `true` if this deque changed as a result of the call addAll(Collection<? extends E> the elements to be inserted into this deque c) Redeclares java.util.Collection.addAll. Adds all of the elements in the specified collection at the end of this deque, as if by calling `addLast` on each one, in the order that they are returned by the collection's iterator.
public void	addFirst(E the element to add e) Redeclares as abstract: java.util.SequencedCollection.addFirst. Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available.
public void	addLast(E the element to add e) Redeclares as abstract: java.util.SequencedCollection.addLast. Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available.
public boolean	Returns: `true` if this deque contains the specified element contains(Object element whose presence in this deque is to be tested o) Redeclares java.util.Collection.contains. Returns `true` if this deque contains the specified element.
public Iterator<E>	Returns: an iterator over the elements in this deque in reverse sequence descendingIterator() Returns an iterator over the elements in this deque in reverse sequential order.
public E	Returns: the head of the queue represented by this deque element() Redeclares java.util.Queue.element. Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).
public E	Returns: the head of this deque getFirst() Redeclares as abstract: java.util.SequencedCollection.getFirst. Retrieves, but does not remove, the first element of this deque.
public E	Returns: the tail of this deque getLast() Redeclares as abstract: java.util.SequencedCollection.getLast. Retrieves, but does not remove, the last element of this deque.
public Iterator<E>	Returns: an iterator over the elements in this deque in proper sequence iterator() Redeclares java.util.Collection.iterator. Returns an iterator over the elements in this deque in proper sequence.
public boolean	Returns: `true` if the element was added to this deque, else `false` offer(E the element to add e) Redeclares java.util.Queue.offer. Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and `false` if no space is currently available.
public boolean	Returns: `true` if the element was added to this deque, else `false` offerFirst(E the element to add e) Inserts the specified element at the front of this deque unless it would violate capacity restrictions.
public boolean	Returns: `true` if the element was added to this deque, else `false` offerLast(E the element to add e) Inserts the specified element at the end of this deque unless it would violate capacity restrictions.
public E	Returns: the head of the queue represented by this deque, or `null` if this deque is empty peek() Redeclares java.util.Queue.peek. Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty.
public E	Returns: the head of this deque, or `null` if this deque is empty peekFirst() Retrieves, but does not remove, the first element of this deque, or returns `null` if this deque is empty.
public E	Returns: the tail of this deque, or `null` if this deque is empty peekLast() Retrieves, but does not remove, the last element of this deque, or returns `null` if this deque is empty.
public E	Returns: the first element of this deque, or `null` if this deque is empty poll() Redeclares java.util.Queue.poll. Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty.
public E	Returns: the head of this deque, or `null` if this deque is empty pollFirst() Retrieves and removes the first element of this deque, or returns `null` if this deque is empty.
public E	Returns: the tail of this deque, or `null` if this deque is empty pollLast() Retrieves and removes the last element of this deque, or returns `null` if this deque is empty.
public E	Returns: the element at the front of this deque (which is the top of the stack represented by this deque) pop() Pops an element from the stack represented by this deque.
public void	push(E the element to push e) Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available.
public E	Returns: the head of the queue represented by this deque remove() Redeclares java.util.Queue.remove. Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).
public boolean	Returns: `true` if an element was removed as a result of this call remove(Object element to be removed from this deque, if present o) Redeclares java.util.Collection.remove. Removes the first occurrence of the specified element from this deque.
public E	Returns: the head of this deque removeFirst() Redeclares as abstract: java.util.SequencedCollection.removeFirst. Retrieves and removes the first element of this deque.
public boolean	Returns: `true` if an element was removed as a result of this call removeFirstOccurrence(Object element to be removed from this deque, if present o) Removes the first occurrence of the specified element from this deque.
public E	Returns: the tail of this deque removeLast() Redeclares as abstract: java.util.SequencedCollection.removeLast. Retrieves and removes the last element of this deque.
public boolean	Returns: `true` if an element was removed as a result of this call removeLastOccurrence(Object element to be removed from this deque, if present o) Removes the last occurrence of the specified element from this deque.
public default Deque<E>	Returns: a reverse-ordered view of this collection, as a `Deque` reversed() Implements java.util.SequencedCollection.reversed. Returns a reverse-ordered view of this collection.
public int	Returns: the number of elements in this deque size() Redeclares java.util.Collection.size. Returns the number of elements in this deque.

Method Detail

add back to summary

add	back to summary
public boolean add(E e) Redeclares java.util.Queue.add, java.util.Collection.add. Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and throwing an `IllegalStateException` if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use `offer`. This method is equivalent to `addLast`. Parameters e:E the element to add Returns:boolean `true` (as specified by `Collection#add`) Exceptions IllegalStateException: if the element cannot be added at this time due to capacity restrictions ClassCastException: if the class of the specified element prevents it from being added to this deque NullPointerException: if the specified element is null and this deque does not permit null elements IllegalArgumentException: if some property of the specified element prevents it from being added to this deque

public boolean add(E e)

Redeclares java.util.Queue.add, java.util.Collection.add.

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use offer.

This method is equivalent to addLast.

Parameters

e:E: the element to add

Returns:boolean

true (as specified by Collection#add)

Exceptions

IllegalStateException:: if the element cannot be added at this time due to capacity restrictions
ClassCastException:: if the class of the specified element prevents it from being added to this deque
NullPointerException:: if the specified element is null and this deque does not permit null elements
IllegalArgumentException:: if some property of the specified element prevents it from being added to this deque

addAll back to summary

addAll	back to summary
public boolean addAll(Collection<? extends E> c) Redeclares java.util.Collection.addAll. Adds all of the elements in the specified collection at the end of this deque, as if by calling `addLast` on each one, in the order that they are returned by the collection's iterator. When using a capacity-restricted deque, it is generally preferable to call `offer` separately on each element. An exception encountered while trying to add an element may result in only some of the elements having been successfully added when the associated exception is thrown. Parameters c:Collection<? extends E> the elements to be inserted into this deque Returns:boolean `true` if this deque changed as a result of the call Exceptions IllegalStateException: if not all the elements can be added at this time due to insertion restrictions ClassCastException: if the class of an element of the specified collection prevents it from being added to this deque NullPointerException: if the specified collection contains a null element and this deque does not permit null elements, or if the specified collection is null IllegalArgumentException: if some property of an element of the specified collection prevents it from being added to this deque

public boolean addAll(Collection<? extends E> c)

Redeclares java.util.Collection.addAll.

Adds all of the elements in the specified collection at the end of this deque, as if by calling addLast on each one, in the order that they are returned by the collection's iterator.

When using a capacity-restricted deque, it is generally preferable to call offer separately on each element.

An exception encountered while trying to add an element may result in only some of the elements having been successfully added when the associated exception is thrown.

Parameters

c:Collection<? extends E>: the elements to be inserted into this deque

Returns:boolean

true if this deque changed as a result of the call

Exceptions

IllegalStateException:: if not all the elements can be added at this time due to insertion restrictions
ClassCastException:: if the class of an element of the specified collection prevents it from being added to this deque
NullPointerException:: if the specified collection contains a null element and this deque does not permit null elements, or if the specified collection is null
IllegalArgumentException:: if some property of an element of the specified collection prevents it from being added to this deque

addFirst back to summary

addFirst	back to summary
public void addFirst(E e) Redeclares as abstract: java.util.SequencedCollection.addFirst. Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use method `offerFirst`. Parameters e:E the element to add Exceptions IllegalStateException: if the element cannot be added at this time due to capacity restrictions ClassCastException: if the class of the specified element prevents it from being added to this deque NullPointerException: if the specified element is null and this deque does not permit null elements IllegalArgumentException: if some property of the specified element prevents it from being added to this deque

public void addFirst(E e)

Redeclares as abstract: java.util.SequencedCollection.addFirst.

Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use method offerFirst.

Parameters

e:E: the element to add

Exceptions

IllegalStateException:: if the element cannot be added at this time due to capacity restrictions
ClassCastException:: if the class of the specified element prevents it from being added to this deque
NullPointerException:: if the specified element is null and this deque does not permit null elements
IllegalArgumentException:: if some property of the specified element prevents it from being added to this deque

addLast back to summary

addLast	back to summary
public void addLast(E e) Redeclares as abstract: java.util.SequencedCollection.addLast. Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use method `offerLast`. This method is equivalent to `add`. Parameters e:E the element to add Exceptions IllegalStateException: if the element cannot be added at this time due to capacity restrictions ClassCastException: if the class of the specified element prevents it from being added to this deque NullPointerException: if the specified element is null and this deque does not permit null elements IllegalArgumentException: if some property of the specified element prevents it from being added to this deque

public void addLast(E e)

Redeclares as abstract: java.util.SequencedCollection.addLast.

Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use method offerLast.

This method is equivalent to add.

Parameters

e:E: the element to add

Exceptions

IllegalStateException:: if the element cannot be added at this time due to capacity restrictions
ClassCastException:: if the class of the specified element prevents it from being added to this deque
NullPointerException:: if the specified element is null and this deque does not permit null elements
IllegalArgumentException:: if some property of the specified element prevents it from being added to this deque

contains back to summary

contains	back to summary
public boolean contains(Object o) Redeclares java.util.Collection.contains. Returns `true` if this deque contains the specified element. More formally, returns `true` if and only if this deque contains at least one element `e` such that `Objects.equals(o, e)`. Parameters o:Object element whose presence in this deque is to be tested Returns:boolean `true` if this deque contains the specified element Exceptions ClassCastException: if the class of the specified element is incompatible with this deque (optional) NullPointerException: if the specified element is null and this deque does not permit null elements (optional)

public boolean contains(Object o)

Redeclares java.util.Collection.contains.

Returns true if this deque contains the specified element. More formally, returns true if and only if this deque contains at least one element e such that Objects.equals(o, e).

Parameters

o:Object: element whose presence in this deque is to be tested

Returns:boolean

true if this deque contains the specified element

Exceptions

ClassCastException:: if the class of the specified element is incompatible with this deque (optional)
NullPointerException:: if the specified element is null and this deque does not permit null elements (optional)

descendingIterator	back to summary
public Iterator<E> descendingIterator() Returns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head). Returns:Iterator<E> an iterator over the elements in this deque in reverse sequence

descendingIterator

back to summary

public Iterator<E> descendingIterator()

Returns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head).

Returns:Iterator<E>: an iterator over the elements in this deque in reverse sequence

element back to summary

element	back to summary
public E element() Redeclares java.util.Queue.element. Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from `peek` only in that it throws an exception if this deque is empty. This method is equivalent to `getFirst()`. Returns:E the head of the queue represented by this deque Exceptions NoSuchElementException: if this deque is empty

public E element()

Redeclares java.util.Queue.element.

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from peek only in that it throws an exception if this deque is empty.

This method is equivalent to getFirst().

Returns:E

the head of the queue represented by this deque

Exceptions

NoSuchElementException:: if this deque is empty

getFirst back to summary

getFirst	back to summary
public E getFirst() Redeclares as abstract: java.util.SequencedCollection.getFirst. Retrieves, but does not remove, the first element of this deque. This method differs from `peekFirst` only in that it throws an exception if this deque is empty. Returns:E the head of this deque Exceptions NoSuchElementException: if this deque is empty

public E getFirst()

Redeclares as abstract: java.util.SequencedCollection.getFirst.

Retrieves, but does not remove, the first element of this deque. This method differs from peekFirst only in that it throws an exception if this deque is empty.

Returns:E

the head of this deque

Exceptions

NoSuchElementException:: if this deque is empty

getLast back to summary

getLast	back to summary
public E getLast() Redeclares as abstract: java.util.SequencedCollection.getLast. Retrieves, but does not remove, the last element of this deque. This method differs from `peekLast` only in that it throws an exception if this deque is empty. Returns:E the tail of this deque Exceptions NoSuchElementException: if this deque is empty

public E getLast()

Redeclares as abstract: java.util.SequencedCollection.getLast.

Retrieves, but does not remove, the last element of this deque. This method differs from peekLast only in that it throws an exception if this deque is empty.

Returns:E

the tail of this deque

Exceptions

NoSuchElementException:: if this deque is empty

iterator	back to summary
public Iterator<E> iterator() Redeclares java.util.Collection.iterator. Returns an iterator over the elements in this deque in proper sequence. The elements will be returned in order from first (head) to last (tail). Returns:Iterator<E> an iterator over the elements in this deque in proper sequence

iterator

back to summary

public Iterator<E> iterator()

Redeclares java.util.Collection.iterator.

Returns an iterator over the elements in this deque in proper sequence. The elements will be returned in order from first (head) to last (tail).

Returns:Iterator<E>: an iterator over the elements in this deque in proper sequence

offer back to summary

offer	back to summary
public boolean offer(E e) Redeclares java.util.Queue.offer. Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and `false` if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the `add` method, which can fail to insert an element only by throwing an exception. This method is equivalent to `offerLast`. Parameters e:E the element to add Returns:boolean `true` if the element was added to this deque, else `false` Exceptions ClassCastException: if the class of the specified element prevents it from being added to this deque NullPointerException: if the specified element is null and this deque does not permit null elements IllegalArgumentException: if some property of the specified element prevents it from being added to this deque

public boolean offer(E e)

Redeclares java.util.Queue.offer.

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the add method, which can fail to insert an element only by throwing an exception.

This method is equivalent to offerLast.

Parameters

e:E: the element to add

Returns:boolean

true if the element was added to this deque, else false

Exceptions

ClassCastException:: if the class of the specified element prevents it from being added to this deque
NullPointerException:: if the specified element is null and this deque does not permit null elements
IllegalArgumentException:: if some property of the specified element prevents it from being added to this deque

offerFirst back to summary

offerFirst	back to summary
public boolean offerFirst(E e) Inserts the specified element at the front of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the `addFirst` method, which can fail to insert an element only by throwing an exception. Parameters e:E the element to add Returns:boolean `true` if the element was added to this deque, else `false` Exceptions ClassCastException: if the class of the specified element prevents it from being added to this deque NullPointerException: if the specified element is null and this deque does not permit null elements IllegalArgumentException: if some property of the specified element prevents it from being added to this deque

public boolean offerFirst(E e)

Inserts the specified element at the front of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the addFirst method, which can fail to insert an element only by throwing an exception.

Parameters

e:E: the element to add

Returns:boolean

true if the element was added to this deque, else false

Exceptions

ClassCastException:: if the class of the specified element prevents it from being added to this deque
NullPointerException:: if the specified element is null and this deque does not permit null elements
IllegalArgumentException:: if some property of the specified element prevents it from being added to this deque

offerLast back to summary

offerLast	back to summary
public boolean offerLast(E e) Inserts the specified element at the end of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the `addLast` method, which can fail to insert an element only by throwing an exception. Parameters e:E the element to add Returns:boolean `true` if the element was added to this deque, else `false` Exceptions ClassCastException: if the class of the specified element prevents it from being added to this deque NullPointerException: if the specified element is null and this deque does not permit null elements IllegalArgumentException: if some property of the specified element prevents it from being added to this deque

public boolean offerLast(E e)

Inserts the specified element at the end of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the addLast method, which can fail to insert an element only by throwing an exception.

Parameters

e:E: the element to add

Returns:boolean

true if the element was added to this deque, else false

Exceptions

ClassCastException:: if the class of the specified element prevents it from being added to this deque
NullPointerException:: if the specified element is null and this deque does not permit null elements
IllegalArgumentException:: if some property of the specified element prevents it from being added to this deque

peek back to summary

peek	back to summary
public E peek() Redeclares java.util.Queue.peek. Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty. This method is equivalent to `peekFirst()`. Returns:E the head of the queue represented by this deque, or `null` if this deque is empty

public E peek()

Redeclares java.util.Queue.peek.

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

This method is equivalent to peekFirst().

Returns:E: the head of the queue represented by this deque, or null if this deque is empty

peekFirst back to summary

peekFirst	back to summary
public E peekFirst() Retrieves, but does not remove, the first element of this deque, or returns `null` if this deque is empty. Returns:E the head of this deque, or `null` if this deque is empty

public E peekFirst()

Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.

Returns:E: the head of this deque, or null if this deque is empty

peekLast back to summary

peekLast	back to summary
public E peekLast() Retrieves, but does not remove, the last element of this deque, or returns `null` if this deque is empty. Returns:E the tail of this deque, or `null` if this deque is empty

public E peekLast()

Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.

Returns:E: the tail of this deque, or null if this deque is empty

poll back to summary

poll	back to summary
public E poll() Redeclares java.util.Queue.poll. Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty. This method is equivalent to `pollFirst()`. Returns:E the first element of this deque, or `null` if this deque is empty

public E poll()

Redeclares java.util.Queue.poll.

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

This method is equivalent to pollFirst().

Returns:E: the first element of this deque, or null if this deque is empty

pollFirst back to summary

pollFirst	back to summary
public E pollFirst() Retrieves and removes the first element of this deque, or returns `null` if this deque is empty. Returns:E the head of this deque, or `null` if this deque is empty

public E pollFirst()

Retrieves and removes the first element of this deque, or returns null if this deque is empty.

Returns:E: the head of this deque, or null if this deque is empty

pollLast back to summary

pollLast	back to summary
public E pollLast() Retrieves and removes the last element of this deque, or returns `null` if this deque is empty. Returns:E the tail of this deque, or `null` if this deque is empty

public E pollLast()

Retrieves and removes the last element of this deque, or returns null if this deque is empty.

Returns:E: the tail of this deque, or null if this deque is empty

pop back to summary

pop	back to summary
public E pop() Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque. This method is equivalent to `removeFirst()`. Returns:E the element at the front of this deque (which is the top of the stack represented by this deque) Exceptions NoSuchElementException: if this deque is empty

public E pop()

Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque.

This method is equivalent to removeFirst().

Returns:E

the element at the front of this deque (which is the top of the stack represented by this deque)

Exceptions

NoSuchElementException:: if this deque is empty

push back to summary

push	back to summary
public void push(E e) Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. This method is equivalent to `addFirst`. Parameters e:E the element to push Exceptions IllegalStateException: if the element cannot be added at this time due to capacity restrictions ClassCastException: if the class of the specified element prevents it from being added to this deque NullPointerException: if the specified element is null and this deque does not permit null elements IllegalArgumentException: if some property of the specified element prevents it from being added to this deque

public void push(E e)

Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.

This method is equivalent to addFirst.

Parameters

e:E: the element to push

Exceptions

IllegalStateException:: if the element cannot be added at this time due to capacity restrictions
ClassCastException:: if the class of the specified element prevents it from being added to this deque
NullPointerException:: if the specified element is null and this deque does not permit null elements
IllegalArgumentException:: if some property of the specified element prevents it from being added to this deque

remove back to summary

remove	back to summary
public E remove() Redeclares java.util.Queue.remove. Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from `poll()` only in that it throws an exception if this deque is empty. This method is equivalent to `removeFirst()`. Returns:E the head of the queue represented by this deque Exceptions NoSuchElementException: if this deque is empty

public E remove()

Redeclares java.util.Queue.remove.

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from poll() only in that it throws an exception if this deque is empty.

This method is equivalent to removeFirst().

Returns:E

the head of the queue represented by this deque

Exceptions

NoSuchElementException:: if this deque is empty

remove back to summary

remove	back to summary
public boolean remove(Object o) Redeclares java.util.Collection.remove. Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element `e` such that `Objects.equals(o, e)` (if such an element exists). Returns `true` if this deque contained the specified element (or equivalently, if this deque changed as a result of the call). This method is equivalent to `removeFirstOccurrence(Object)`. Parameters o:Object element to be removed from this deque, if present Returns:boolean `true` if an element was removed as a result of this call Exceptions ClassCastException: if the class of the specified element is incompatible with this deque (optional) NullPointerException: if the specified element is null and this deque does not permit null elements (optional)

public boolean remove(Object o)

Redeclares java.util.Collection.remove.

Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element e such that Objects.equals(o, e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

This method is equivalent to removeFirstOccurrence(Object).

Parameters

o:Object: element to be removed from this deque, if present

Returns:boolean

true if an element was removed as a result of this call

Exceptions

ClassCastException:: if the class of the specified element is incompatible with this deque (optional)
NullPointerException:: if the specified element is null and this deque does not permit null elements (optional)

removeFirst back to summary

removeFirst	back to summary
public E removeFirst() Redeclares as abstract: java.util.SequencedCollection.removeFirst. Retrieves and removes the first element of this deque. This method differs from `pollFirst` only in that it throws an exception if this deque is empty. Returns:E the head of this deque Exceptions NoSuchElementException: if this deque is empty

public E removeFirst()

Redeclares as abstract: java.util.SequencedCollection.removeFirst.

Retrieves and removes the first element of this deque. This method differs from pollFirst only in that it throws an exception if this deque is empty.

Returns:E

the head of this deque

Exceptions

NoSuchElementException:: if this deque is empty

removeFirstOccurrence back to summary

removeFirstOccurrence	back to summary
public boolean removeFirstOccurrence(Object o) Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element `e` such that `Objects.equals(o, e)` (if such an element exists). Returns `true` if this deque contained the specified element (or equivalently, if this deque changed as a result of the call). Parameters o:Object element to be removed from this deque, if present Returns:boolean `true` if an element was removed as a result of this call Exceptions ClassCastException: if the class of the specified element is incompatible with this deque (optional) NullPointerException: if the specified element is null and this deque does not permit null elements (optional)

public boolean removeFirstOccurrence(Object o)

Parameters

o:Object: element to be removed from this deque, if present

Returns:boolean

true if an element was removed as a result of this call

Exceptions

ClassCastException:: if the class of the specified element is incompatible with this deque (optional)
NullPointerException:: if the specified element is null and this deque does not permit null elements (optional)

removeLast back to summary

removeLast	back to summary
public E removeLast() Redeclares as abstract: java.util.SequencedCollection.removeLast. Retrieves and removes the last element of this deque. This method differs from `pollLast` only in that it throws an exception if this deque is empty. Returns:E the tail of this deque Exceptions NoSuchElementException: if this deque is empty

public E removeLast()

Redeclares as abstract: java.util.SequencedCollection.removeLast.

Retrieves and removes the last element of this deque. This method differs from pollLast only in that it throws an exception if this deque is empty.

Returns:E

the tail of this deque

Exceptions

NoSuchElementException:: if this deque is empty

removeLastOccurrence back to summary

removeLastOccurrence	back to summary
public boolean removeLastOccurrence(Object o) Removes the last occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the last element `e` such that `Objects.equals(o, e)` (if such an element exists). Returns `true` if this deque contained the specified element (or equivalently, if this deque changed as a result of the call). Parameters o:Object element to be removed from this deque, if present Returns:boolean `true` if an element was removed as a result of this call Exceptions ClassCastException: if the class of the specified element is incompatible with this deque (optional) NullPointerException: if the specified element is null and this deque does not permit null elements (optional)

public boolean removeLastOccurrence(Object o)

Removes the last occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the last element e such that Objects.equals(o, e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Parameters

o:Object: element to be removed from this deque, if present

Returns:boolean

true if an element was removed as a result of this call

Exceptions

ClassCastException:: if the class of the specified element is incompatible with this deque (optional)
NullPointerException:: if the specified element is null and this deque does not permit null elements (optional)

reversed back to summary

reversed	back to summary
public default Deque<E> reversed() Implements java.util.SequencedCollection.reversed. Doc from java.util.SequencedCollection.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. Implementation Specification The implementation in this interface returns a reverse-ordered Deque view. The `reversed()` method of the view returns a reference to this Deque. Other operations on the view are implemented via calls to public methods on this Deque. The exact relationship between calls on the view and calls on this Deque is unspecified. However, order-sensitive operations generally behave as if they delegate to the appropriate method with the opposite orientation. For example, calling `getFirst` on the view might result in a call to `getLast` on this Deque. Returns:Deque<E> a reverse-ordered view of this collection, as a `Deque` Since 21

public default Deque<E> reversed()

Implements java.util.SequencedCollection.reversed.

Doc from java.util.SequencedCollection.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.

Implementation Specification

The implementation in this interface returns a reverse-ordered Deque view. The reversed() method of the view returns a reference to this Deque. Other operations on the view are implemented via calls to public methods on this Deque. The exact relationship between calls on the view and calls on this Deque is unspecified. However, order-sensitive operations generally behave as if they delegate to the appropriate method with the opposite orientation. For example, calling getFirst on the view might result in a call to getLast on this Deque.

Returns:Deque<E>: a reverse-ordered view of this collection, as a Deque
Since: 21

size	back to summary
public int size() Redeclares java.util.Collection.size. Returns the number of elements in this deque. Returns:int the number of elements in this deque

size

back to summary

public int size()

Redeclares java.util.Collection.size.

Returns the number of elements in this deque.

Returns:int: the number of elements in this deque

public Interface Deque<E>

Method Summary

Method Detail