Deque (Codename One API)

Type Parameters:

E - the type of elements in this collection

All Superinterfaces:

Collection<E>, Iterable<E>, Queue<E>

All Known Implementing Classes:

ArrayDeque, LinkedList
```
public interface Deque<E>
extends Queue<E>
```
A kind of collection that can insert or remove element at both ends("double ended queue"). Mostly a deque has no limit of its size. Extending from Queue, a deque can be used as a Queue which behavior is first-in-first-out. Furthermore, a deque can also be used as a Stack(legacy class) which behavior is last-in-first-out. A typical deque does not allow null to be inserted as its element, while some implementations allow it. But null should not be inserted even in these implementations, since method poll return null to indicate that there is no element left in the deque. A deque can also remove interior elements by removeFirstOccurrence and removeLastOccurrence methods. A deque can not access elements by index.

Since:

1.6

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`void`	`addFirst(E e)` Inserts an element at the head of this deque if it dose not violate size limit immediately.
`void`	`addLast(E e)` Inserts an element at the tail of this deque if it dose not violate size limit immediately.
`Iterator<E>`	`descendingIterator()` Returns the iterator in reverse order, from tail to head.
`E`	`getFirst()` Gets but not removes the head element of this deque.
`E`	`getLast()` Gets but not removes the tail element of this deque.
`boolean`	`offerFirst(E e)` Inserts an element at the head of this deque unless it would violate size limit.
`boolean`	`offerLast(E e)` Inserts an element at the tail of this deque unless it would violate size limit.
`E`	`peekFirst()` Gets but not removes the head element of this deque.
`E`	`peekLast()` Gets but not removes the tail element of this deque.
`E`	`pollFirst()` Gets and removes the head element of this deque.
`E`	`pollLast()` Gets and removes the tail element of this deque.
`E`	`pop()` Pops the head element of the deque, just same as removeFirst().
`void`	`push(E e)` Pushes the element to the deque(at the head of the deque), just same as addFirst(E).
`E`	`removeFirst()` Gets and removes the head element of this deque.
`boolean`	`removeFirstOccurrence(Object o)` Removes the first equivalent element of the specified object.
`E`	`removeLast()` Gets and removes the tail element of this deque.
`boolean`	`removeLastOccurrence(Object o)` Removes the last equivalent element of the specified object.

Methods inherited from interface java.util.Queue
element, offer, peek, poll, remove

Methods inherited from interface java.util.Collection
add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray

- Method Detail
  - addFirst
```
void addFirst(E e)
```
    Inserts an element at the head of this deque if it dose not violate size limit immediately. It is better to use offerFirst(E) if a deque is size-limited.
    
    Parameters:
    
    e - the element
    
    Throws:
    
    IllegalStateException - if it can not add now due to size limit
    
    ClassCastException - if the class of element can not be added into this deque
    
    NullPointerException - if the element is null and the deque can not contain null element
    
    IllegalArgumentException - if the element can not be added due to some property.
  - addLast
```
void addLast(E e)
```
    Inserts an element at the tail of this deque if it dose not violate size limit immediately. It is better to use offerLast(E) if a deque is size-limited.
    
    Parameters:
    
    e - the element
    
    Throws:
    
    IllegalStateException - if it can not add now due to size limit
    
    ClassCastException - if the class of element can not be added into this deque
    
    NullPointerException - if the element is null and the deque can not contain null element
    
    IllegalArgumentException - if the element can not be added due to some property.
  - offerFirst
```
boolean offerFirst(E e)
```
    Inserts an element at the head of this deque unless it would violate size limit. It is better than the addFirst(E) method in a size-limited deque, because the latter one may fail to add the element only by throwing an exception.
    
    Parameters:
    
    e - the element
    
    Returns:
    
    true if the operation succeeds or false if it fails.
    
    Throws:
    
    ClassCastException - if the class of element can not be added into this deque
    
    NullPointerException - if the element is null and the deque can not contain null element
    
    IllegalArgumentException - if the element can not be added due to some property.
  - offerLast
```
boolean offerLast(E e)
```
    Inserts an element at the tail of this deque unless it would violate size limit. It is better than the addLast(E) method in a size-limited deque, because the latter one may fail to add the element only by throwing an exception.
    
    Parameters:
    
    e - the element
    
    Returns:
    
    true if the operation succeeds or false if it fails
    
    Throws:
    
    ClassCastException - if the class of element can not be added into this deque
    
    NullPointerException - if the element is null and the deque can not contain null element
    
    IllegalArgumentException - if the element can not be added due to some property
  - removeFirst
```
E removeFirst()
```
    Gets and removes the head element of this deque. This method throws an exception if the deque is empty.
    
    Returns:
    
    the head element
    
    Throws:
    
    NoSuchElementException - if the deque is empty
  - removeLast
```
E removeLast()
```
    Gets and removes the tail element of this deque. This method throws an exception if the deque is empty.
    
    Returns:
    
    the tail element
    
    Throws:
    
    NoSuchElementException - if the deque is empty
  - pollFirst
```
E pollFirst()
```
    Gets and removes the head element of this deque. This method returns null if the deque is empty.
    
    Returns:
    
    the head element or null if the deque is empty
  - pollLast
```
E pollLast()
```
    Gets and removes the tail element of this deque. This method returns null if the deque is empty.
    
    Returns:
    
    the tail element or null if the deque is empty
  - getFirst
```
E getFirst()
```
    Gets but not removes the head element of this deque. This method throws an exception if the deque is empty.
    
    Returns:
    
    the head element
    
    Throws:
    
    NoSuchElementException - if the deque is empty
  - getLast
```
E getLast()
```
    Gets but not removes the tail element of this deque. This method throws an exception if the deque is empty.
    
    Returns:
    
    the tail element
    
    Throws:
    
    NoSuchElementException - if the deque is empty
  - peekFirst
```
E peekFirst()
```
    Gets but not removes the head element of this deque. This method returns null if the deque is empty.
    
    Returns:
    
    the head element or null if the deque is empty
  - peekLast
```
E peekLast()
```
    Gets but not removes the tail element of this deque. This method returns null if the deque is empty.
    
    Returns:
    
    the tail element or null if the deque is empty
  - removeFirstOccurrence
```
boolean removeFirstOccurrence(Object o)
```
    Removes the first equivalent element of the specified object. If the deque does not contain the element, it is unchanged and returns false.
    
    Parameters:
    
    o - the element to be removed
    
    Returns:
    
    true if the operation succeeds or false if the deque does not contain the element.
    
    Throws:
    
    ClassCastException - if the class of the element is incompatible with the deque
    
    NullPointerException - if the element is null and the deque can not contain null element
  - removeLastOccurrence
```
boolean removeLastOccurrence(Object o)
```
    Removes the last equivalent element of the specified object. If the deque does not contain the element, it is unchanged and returns false.
    
    Parameters:
    
    o - the element to be removed
    
    Returns:
    
    true if the operation succeeds or false if the deque does not contain the element.
    
    Throws:
    
    ClassCastException - if the class of the element is incompatible with the deque
    
    NullPointerException - if the element is null and the deque can not contain null element
  - push
```
void push(E e)
```
    Pushes the element to the deque(at the head of the deque), just same as addFirst(E).
    
    Parameters:
    
    e - the element
    
    Throws:
    
    IllegalStateException - if it can not add now due to size limit
    
    ClassCastException - if the class of element can not be added into this deque
    
    NullPointerException - if the element is null and the deque can not contain null element
    
    IllegalArgumentException - if the element can not be added due to some property.
  - pop
```
E pop()
```
    Pops the head element of the deque, just same as removeFirst().
    
    Returns:
    
    the head element
    
    Throws:
    
    NoSuchElementException - if the deque is empty
  - descendingIterator
```
Iterator<E> descendingIterator()
```
    Returns the iterator in reverse order, from tail to head.
    
    Returns:
    
    the iterator in reverse order

Interface Deque<E>

Method Summary

Methods inherited from interface java.util.Queue

Methods inherited from interface java.util.Collection

Method Detail

addFirst

addLast

offerFirst

offerLast

removeFirst

removeLast

pollFirst

pollLast

getFirst

getLast

peekFirst

peekLast

removeFirstOccurrence

removeLastOccurrence

push

pop

descendingIterator