Class ArrayDeque<E>

java.lang.Object
java.util.AbstractCollection<E>
java.util.ArrayDeque<E>
All Implemented Interfaces:
Iterable<E>, Collection<E>, Deque<E>, Queue<E>
public class ArrayDeque<E> extends AbstractCollection<E> implements Deque<E>

An implementation of Deque, backed by an array.

ArrayDeques have no size limit, can not contain null element, and they are not thread-safe.

All optional operations are supported, and the elements can be any objects.

Type parameter E: the type of elements in this collection

Since

1.6

  • Constructor Summary

    Constructors
    Constructor
    Description
    ArrayDeque()
    Constructs a new empty instance of ArrayDeque big enough for 16 elements.
    ArrayDeque(int minSize)
    Constructs a new empty instance of ArrayDeque big enough for specified number of elements.
    ArrayDeque(Collection<? extends E> c)
    Constructs a new instance of ArrayDeque containing the elements of the specified collection, with the order returned by the collection's iterator.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    add(E e)
    Inserts the element to the tail of the deque.
    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.
    void
    clear()
    Empty the deque.
    boolean
    contains(Object obj)
    Returns true if the specified element is in the deque.
    Iterator<E>
    descendingIterator()
    Returns the iterator in reverse order, from tail to head.
    E
    element()
    Gets but does not remove the head element of this deque.
    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
    isEmpty()
    Returns true if the deque has no elements.
    Iterator<E>
    iterator()
    Returns the iterator of the deque.
    boolean
    offer(E e)
    Inserts the element at the tail of the 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
    peek()
    Gets but not removes the head element of this deque.
    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
    poll()
    Gets and removes the head 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
    remove()
    Gets and removes the head element of this deque.
    boolean
    remove(Object obj)
    Removes the first equivalent element of the specified object.
    E
    removeFirst()
    Gets and removes the head element of this deque.
    boolean
    removeFirstOccurrence(Object obj)
    Removes the first equivalent element of the specified object.
    E
    removeLast()
    Gets and removes the tail element of this deque.
    boolean
    removeLastOccurrence(Object obj)
    Removes the last equivalent element of the specified object.
    int
    size()
    Returns the size of the deque.

    Methods inherited from class AbstractCollection

    addAll, containsAll, removeAll, retainAll, toArray, toArray, toString

    Methods inherited from class Object

    clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

    Methods inherited from interface Collection

    addAll, containsAll, equals, hashCode, removeAll, retainAll, toArray, toArray

  • Constructor Details

    • ArrayDeque

      public ArrayDeque()
      Constructs a new empty instance of ArrayDeque big enough for 16 elements.

    • ArrayDeque

      public ArrayDeque(int minSize)

      Constructs a new empty instance of ArrayDeque big enough for specified number of elements.

      Parameters
      • minSize: the smallest size of the ArrayDeque

    • ArrayDeque

      public ArrayDeque(Collection<? extends E> c)

      Constructs a new instance of ArrayDeque containing the elements of the specified collection, with the order returned by the collection's iterator.

      Parameters
      • c: the source of the elements
      Throws
      • NullPointerException: if the collection is null

  • Method Details

    • addFirst

      public 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: @throws 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.

      Parameters
      • e: the element
      Throws
      • NullPointerException: if the element is null
      See also
      • java.util.Deque#addFirst(java.lang.Object)
      Specified by:
      addFirst in interface Deque<E>

    • addLast

      public 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: @throws 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.

      Parameters
      • e: the element
      Throws
      • NullPointerException: if the element is null
      See also
      • java.util.Deque#addLast(java.lang.Object)
      Specified by:
      addLast in interface Deque<E>

    • offerFirst

      public 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: @throws 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.

      Parameters
      • e: the element
      Returns

      true

      Throws
      • NullPointerException: if the element is null
      See also
      • java.util.Deque#offerFirst(java.lang.Object)
      Specified by:
      offerFirst in interface Deque<E>

    • offerLast

      public 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: @throws 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

      Parameters
      • e: the element
      Returns

      true if the operation succeeds or false if it fails

      Throws
      • NullPointerException: if the element is null
      See also
      • java.util.Deque#offerLast(java.lang.Object)
      Specified by:
      offerLast in interface Deque<E>

    • offer

      public boolean offer(E e)

      Inserts the element at the tail of the deque.

      Parameters
      • e: the element
      Returns

      true if the operation succeeds or false if it fails.

      Throws
      • NullPointerException: if the element is null
      See also
      • java.util.Queue#offer(java.lang.Object)
      Specified by:
      offer in interface Queue<E>
      Returns:
      true if the operation succeeds and false if it fails.

    • add

      public boolean add(E e)

      Inserts the element to the tail of the deque.

      Parameters
      • e: the element
      Returns

      true

      See also
      • java.util.AbstractCollection#add(java.lang.Object)
      Specified by:
      add in interface Collection<E>
      Overrides:
      add in class AbstractCollection<E>
      Returns:

      true if this Collection is modified, false otherwise.

      Throws

      • UnsupportedOperationException: if adding to this Collection is not supported.

      • ClassCastException: @throws ClassCastException if the class of the object is inappropriate for this collection.

      • IllegalArgumentException: if the object cannot be added to this Collection.

      • NullPointerException: if null elements cannot be added to the Collection.

    • push

      public 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: @throws 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.

      Parameters
      • e: the element to push
      Throws
      • NullPointerException: if the element is null
      See also
      • java.util.Deque#push(java.lang.Object)
      Specified by:
      push in interface Deque<E>

    • removeFirst

      public 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
      Returns

      the head element

      Throws
      • NoSuchElementException: if the deque is empty
      See also
      • java.util.Deque#removeFirst()
      Specified by:
      removeFirst in interface Deque<E>

    • remove

      public E remove()

      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
      See also
      • java.util.Queue#remove()
      Specified by:
      remove in interface Queue<E>

    • pop

      public E pop()

      Pops the head element of the deque, just same as removeFirst().

      Returns

      the head element

      Throws
      • NoSuchElementException: if the deque is empty
      Returns

      the head element

      Throws
      • NoSuchElementException: if the deque is empty
      See also
      • java.util.Deque#pop()
      Specified by:
      pop in interface Deque<E>

    • removeLast

      public 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
      Returns

      the tail element

      Throws
      • NoSuchElementException: if the deque is empty
      See also
      • java.util.Deque#removeLast()
      Specified by:
      removeLast in interface Deque<E>

    • pollFirst

      public 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

      Returns

      the head element or null if the deque is empty

      See also
      • java.util.Deque#pollFirst()
      Specified by:
      pollFirst in interface Deque<E>

    • poll

      public E poll()

      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

      See also
      • java.util.Queue#poll()
      Specified by:
      poll in interface Queue<E>
      Returns:
      the element at the head of the queue or null if there is no element in the queue.

    • pollLast

      public 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

      Returns

      the tail element or null if the deque is empty

      See also
      • java.util.Deque#pollLast()
      Specified by:
      pollLast in interface Deque<E>

    • getFirst

      public 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
      Returns

      the head element

      Throws
      • NoSuchElementException: if the deque is empty
      See also
      • java.util.Deque#getFirst()
      Specified by:
      getFirst in interface Deque<E>

    • element

      public E element()

      Gets but does not remove the head element of this deque. It throws an exception if the deque is empty.

      Returns

      the head element

      Throws
      • NoSuchElementException: if the deque is empty
      See also
      • java.util.Queue#element()
      Specified by:
      element in interface Queue<E>

    • getLast

      public 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
      Returns

      the tail element

      Throws
      • NoSuchElementException: if the deque is empty
      See also
      • java.util.Deque#getLast()
      Specified by:
      getLast in interface Deque<E>

    • peekFirst

      public 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

      Returns

      the head element or null if the deque is empty

      See also
      • java.util.Deque#peekFirst()
      Specified by:
      peekFirst in interface Deque<E>

    • peek

      public E peek()

      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

      See also
      • java.util.Queue#peek()
      Specified by:
      peek in interface Queue<E>
      Returns:
      the element at the head of the queue or null if there is no element in the queue.

    • peekLast

      public 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

      Returns

      the tail element or null if the deque is empty

      See also
      • java.util.Deque#peekLast()
      Specified by:
      peekLast in interface Deque<E>

    • removeFirstOccurrence

      public boolean removeFirstOccurrence(Object obj)

      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
      Parameters
      • obj: the element to be removed
      Returns
      Specified by:
      removeFirstOccurrence in interface Deque<E>
      Returns:

      true if the operation succeeds or false if the deque does not contain the element

      See also
      • java.util.Deque#removeFirstOccurrence(java.lang.Object)

    • remove

      public boolean remove(Object obj)

      Removes the first equivalent element of the specified object. If the deque does not contain the element, it is unchanged and returns false.

      Parameters
      • obj: the element to be removed
      Returns
      Specified by:
      remove in interface Collection<E>
      Overrides:
      remove in class AbstractCollection<E>
      Returns:

      true if the operation succeeds or false if the deque does not contain the element

      See also
      • java.util.AbstractCollection#remove(java.lang.Object)

    • removeLastOccurrence

      public boolean removeLastOccurrence(Object obj)

      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
      Parameters
      • obj: the element to be removed
      Returns
      Specified by:
      removeLastOccurrence in interface Deque<E>
      Returns:

      true if the operation succeeds or false if the deque does not contain the element.

      See also
      • java.util.Deque#removeLastOccurrence(java.lang.Object)

    • size

      public int size()

      Returns the size of the deque.

      Returns

      the size of the deque

      See also
      • java.util.AbstractCollection#size()
      Specified by:
      size in interface Collection<E>
      Specified by:
      size in class AbstractCollection<E>
      Returns:
      how many objects this Collection contains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in this Collection.

    • isEmpty

      public boolean isEmpty()

      Returns true if the deque has no elements.

      Returns

      true if the deque has no elements, false otherwise

      See also
      • java.util.AbstractCollection#isEmpty()
      Specified by:
      isEmpty in interface Collection<E>
      Overrides:
      isEmpty in class AbstractCollection<E>
      Returns:

      true if this Collection has no elements, false otherwise.

      See also
      • #size

    • contains

      public boolean contains(Object obj)

      Returns true if the specified element is in the deque.

      Parameters
      • obj: the element
      Returns

      true if the element is in the deque, false otherwise

      See also
      • java.util.AbstractCollection#contains(java.lang.Object)
      Specified by:
      contains in interface Collection<E>
      Overrides:
      contains in class AbstractCollection<E>
      Returns:

      true if object is an element of this Collection, false otherwise.

      Throws

      • ClassCastException: @throws ClassCastException if the object to look for isn't of the correct type.

      • NullPointerException: @throws NullPointerException if the object to look for is null and this Collection doesn't support null elements.

    • clear

      public void clear()

      Empty the deque.

      See also
      • java.util.AbstractCollection#clear()
      Specified by:
      clear in interface Collection<E>
      Overrides:
      clear in class AbstractCollection<E>

    • iterator

      public Iterator<E> iterator()

      Returns the iterator of the deque. The elements will be ordered from head to tail.

      Returns

      the iterator

      See also
      • java.util.AbstractCollection#iterator()
      Specified by:
      iterator in interface Collection<E>
      Specified by:
      iterator in interface Iterable<E>
      Specified by:
      iterator in class AbstractCollection<E>

    • descendingIterator

      public Iterator<E> descendingIterator()

      Returns the iterator in reverse order, from tail to head.

      Returns

      the iterator in reverse order

      Returns

      the reverse order Iterator

      See also
      • java.util.Deque#descendingIterator()
      Specified by:
      descendingIterator in interface Deque<E>