| java.util.Deque
| Deque | | public interface Deque extends Queue<E>(Code) | | 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:
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
Deque.peek 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,
Deque.removeFirstOccurrence removeFirstOccurrence and
Deque.removeLastOccurrence 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 indicated 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.
author:
Doug Lea
author:
Josh Bloch
since:
1.6<
Parameters:
E - > the type of elements held in this collection |
| Method Summary | |
| boolean | add(E e)
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. | | void | addFirst(E e)
Inserts the specified element at the front of this deque if it is
possible to do so immediately without violating capacity restrictions. | | void | addLast(E e)
Inserts the specified element at the end of this deque if it is
possible to do so immediately without violating capacity restrictions. | | boolean | contains(Object o)
Returns true if this deque contains the specified element. | | Iterator<E> | descendingIterator()
Returns an iterator over the elements in this deque in reverse
sequential order. | | E | element()
Retrieves, but does not remove, the head of the queue represented by
this deque (in other words, the first element of this deque). | | E | getFirst()
Retrieves, but does not remove, the first element of this deque. | | E | getLast()
Retrieves, but does not remove, the last element of this deque. | | Iterator<E> | iterator()
Returns an iterator over the elements in this deque in proper sequence. | | boolean | offer(E e)
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. | | boolean | offerFirst(E e)
Inserts the specified element at the front of this deque unless it would
violate capacity restrictions. | | boolean | offerLast(E e)
Inserts the specified element at the end of this deque unless it would
violate capacity restrictions. | | E | 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. | | E | peekFirst()
Retrieves, but does not remove, the first element of this deque,
or returns null if this deque is empty. | | E | peekLast()
Retrieves, but does not remove, the last element of this deque,
or returns null if this deque is empty. | | E | 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. | | E | pollFirst()
Retrieves and removes the first element of this deque,
or returns null if this deque is empty. | | E | pollLast()
Retrieves and removes the last element of this deque,
or returns null if this deque is empty. | | E | pop()
Pops an element from the stack represented by this deque. | | 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, returning
true upon success and throwing an
IllegalStateException if no space is currently available. | | E | remove()
Retrieves and removes the head of the queue represented by this deque
(in other words, the first element of this deque). | | boolean | remove(Object o)
Removes the first occurrence of the specified element from this deque. | | E | removeFirst()
Retrieves and removes the first element of this deque. | | boolean | removeFirstOccurrence(Object o)
Removes the first occurrence of the specified element from this deque. | | E | removeLast()
Retrieves and removes the last element of this deque. | | boolean | removeLastOccurrence(Object o)
Removes the last occurrence of the specified element from this deque. | | public int | size()
Returns the number of elements in this deque. |
| add | | boolean add(E e)(Code) | | 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
Deque.offer(Object) offer .
This method is equivalent to
Deque.addLast .
Parameters:
e - the element to add true (as specified by Collection.add)
throws:
IllegalStateException - if the element cannot be added at thistime due to capacity restrictions
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this deque
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements
throws:
IllegalArgumentException - if some property of the specifiedelement prevents it from being added to this deque |
| addFirst | | void addFirst(E e)(Code) | | Inserts the specified element at the front of this deque if it is
possible to do so immediately without violating capacity restrictions.
When using a capacity-restricted deque, it is generally preferable to
use method
Deque.offerFirst .
Parameters:
e - the element to add
throws:
IllegalStateException - if the element cannot be added at thistime due to capacity restrictions
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this deque
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements
throws:
IllegalArgumentException - if some property of the specifiedelement prevents it from being added to this deque |
| addLast | | void addLast(E e)(Code) | | Inserts the specified element at the end of this deque if it is
possible to do so immediately without violating capacity restrictions.
When using a capacity-restricted deque, it is generally preferable to
use method
Deque.offerLast .
This method is equivalent to
Deque.add .
Parameters:
e - the element to add
throws:
IllegalStateException - if the element cannot be added at thistime due to capacity restrictions
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this deque
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements
throws:
IllegalArgumentException - if some property of the specifiedelement prevents it from being added to this deque |
| contains | | boolean contains(Object o)(Code) | | 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
(o==null ? e==null : o.equals(e)).
Parameters:
o - element whose presence in this deque is to be tested true if this deque contains the specified element
throws:
ClassCastException - if the type of the specified elementis incompatible with this deque (optional)
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements (optional) |
| descendingIterator | | Iterator<E> descendingIterator()(Code) | | 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).
an iterator over the elements in this deque in reversesequence |
| element | | E element()(Code) | | 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
Deque.peek peek only in that it throws an
exception if this deque is empty.
This method is equivalent to
Deque.getFirst() .
the head of the queue represented by this deque
throws:
NoSuchElementException - if this deque is empty |
| getFirst | | E getFirst()(Code) | | Retrieves, but does not remove, the first element of this deque.
This method differs from
Deque.peekFirst peekFirst only in that it
throws an exception if this deque is empty.
the head of this deque
throws:
NoSuchElementException - if this deque is empty |
| getLast | | E getLast()(Code) | | Retrieves, but does not remove, the last element of this deque.
This method differs from
Deque.peekLast peekLast only in that it
throws an exception if this deque is empty.
the tail of this deque
throws:
NoSuchElementException - if this deque is empty |
| iterator | | Iterator<E> iterator()(Code) | | 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).
an iterator over the elements in this deque in proper sequence |
| offer | | boolean offer(E e)(Code) | | 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
Deque.add method, which can fail to
insert an element only by throwing an exception.
This method is equivalent to
Deque.offerLast .
Parameters:
e - the element to add true if the element was added to this deque, elsefalse
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this deque
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements
throws:
IllegalArgumentException - if some property of the specifiedelement prevents it from being added to this deque |
| offerFirst | | boolean offerFirst(E e)(Code) | | 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
Deque.addFirst method,
which can fail to insert an element only by throwing an exception.
Parameters:
e - the element to add true if the element was added to this deque, elsefalse
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this deque
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements
throws:
IllegalArgumentException - if some property of the specifiedelement prevents it from being added to this deque |
| offerLast | | boolean offerLast(E e)(Code) | | 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
Deque.addLast method,
which can fail to insert an element only by throwing an exception.
Parameters:
e - the element to add true if the element was added to this deque, elsefalse
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this deque
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements
throws:
IllegalArgumentException - if some property of the specifiedelement prevents it from being added to this deque |
| peek | | E peek()(Code) | | 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
Deque.peekFirst() .
the head of the queue represented by this deque, ornull if this deque is empty |
| peekFirst | | E peekFirst()(Code) | | Retrieves, but does not remove, the first element of this deque,
or returns null if this deque is empty.
the head of this deque, or null if this deque is empty |
| peekLast | | E peekLast()(Code) | | Retrieves, but does not remove, the last element of this deque,
or returns null if this deque is empty.
the tail of this deque, or null if this deque is empty |
| poll | | E poll()(Code) | | 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
Deque.pollFirst() .
the first element of this deque, or null ifthis deque is empty |
| pollFirst | | E pollFirst()(Code) | | Retrieves and removes the first element of this deque,
or returns null if this deque is empty.
the head of this deque, or null if this deque is empty |
| pollLast | | E pollLast()(Code) | | Retrieves and removes the last element of this deque,
or returns null if this deque is empty.
the tail of this deque, or null if this deque is empty |
| pop | | E pop()(Code) | | 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
Deque.removeFirst() .
the element at the front of this deque (which is the topof the stack represented by this deque)
throws:
NoSuchElementException - if this deque is empty |
| push | | void push(E e)(Code) | | 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, returning
true upon success and throwing an
IllegalStateException if no space is currently available.
This method is equivalent to
Deque.addFirst .
Parameters:
e - the element to push
throws:
IllegalStateException - if the element cannot be added at thistime due to capacity restrictions
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this deque
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements
throws:
IllegalArgumentException - if some property of the specifiedelement prevents it from being added to this deque |
| remove | | E remove()(Code) | | 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
Deque.poll poll only in that it throws an
exception if this deque is empty.
This method is equivalent to
Deque.removeFirst() .
the head of the queue represented by this deque
throws:
NoSuchElementException - if this deque is empty |
| remove | | boolean remove(Object o)(Code) | | 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
(o==null ? e==null : o.equals(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
Deque.removeFirstOccurrence .
Parameters:
o - element to be removed from this deque, if present true if an element was removed as a result of this call
throws:
ClassCastException - if the class of the specified elementis incompatible with this deque (optional)
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements (optional) |
| removeFirst | | E removeFirst()(Code) | | Retrieves and removes the first element of this deque. This method
differs from
Deque.pollFirst pollFirst only in that it throws an
exception if this deque is empty.
the head of this deque
throws:
NoSuchElementException - if this deque is empty |
| removeFirstOccurrence | | boolean removeFirstOccurrence(Object o)(Code) | | 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
(o==null ? e==null : o.equals(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 - element to be removed from this deque, if present true if an element was removed as a result of this call
throws:
ClassCastException - if the class of the specified elementis incompatible with this deque (optional)
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements (optional) |
| removeLast | | E removeLast()(Code) | | Retrieves and removes the last element of this deque. This method
differs from
Deque.pollLast pollLast only in that it throws an
exception if this deque is empty.
the tail of this deque
throws:
NoSuchElementException - if this deque is empty |
| removeLastOccurrence | | boolean removeLastOccurrence(Object o)(Code) | | 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
(o==null ? e==null : o.equals(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 - element to be removed from this deque, if present true if an element was removed as a result of this call
throws:
ClassCastException - if the class of the specified elementis incompatible with this deque (optional)
throws:
NullPointerException - if the specified element is null and thisdeque does not permit null elements (optional) |
| size | | public int size()(Code) | | Returns the number of elements in this deque.
the number of elements in this deque |
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