Package org.apache.commons.collections4.queue

Class CircularFifoQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

org.apache.commons.collections4.queue.CircularFifoQueue<E>

Type Parameters:

E - the type of elements in this collection

All Implemented Interfaces:

Serializable, Iterable<E>, Collection<E>, Queue<E>, BoundedCollection<E>

public class CircularFifoQueue<E>
extends AbstractCollection<E>
implements Queue<E>, BoundedCollection<E>, Serializable

CircularFifoQueue is a first-in first-out queue with a fixed size that replaces its oldest element if full.

The removal order of a CircularFifoQueue is based on the insertion order; elements are removed in the same order in which they were added. The iteration order is the same as the removal order.

The add(Object), remove(), peek(), poll(), offer(Object) operations all perform in constant time. All other operations perform in linear time or worse.

This queue prevents null objects from being added.

Since:

4.0

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor	Description
CircularFifoQueue()	Constructor that creates a queue with the default size of 32.
CircularFifoQueue(int size)	Constructor that creates a queue with the specified size.
CircularFifoQueue(Collection<? extends E> coll)	Constructor that creates a queue from the specified collection.

Method Summary

Modifier and Type	Method	Description
boolean	add(E element)	Adds the given element to this queue.
void	clear()	Clears this queue.
E	element()
E	get(int index)	Returns the element at the specified position in this queue.
boolean	isAtFullCapacity()	Returns true if the capacity limit of this queue has been reached, i.e.
boolean	isEmpty()	Returns true if this queue is empty; false otherwise.
boolean	isFull()	Returns true if this collection is full and no new elements can be added.
Iterator<E>	iterator()	Returns an iterator over this queue's elements.
int	maxSize()	Gets the maximum size of the collection (the bound).
boolean	offer(E element)	Adds the given element to this queue.
E	peek()
E	poll()
E	remove()
int	size()	Returns the number of elements stored in the queue.

Methods inherited from class java.util.AbstractCollection

addAll, contains, containsAll, remove, removeAll, retainAll, toArray, toArray, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Collection

addAll, contains, containsAll, equals, hashCode, parallelStream, remove, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray, toArray

Methods inherited from interface java.lang.Iterable

forEach

Constructor Detail

CircularFifoQueue

public CircularFifoQueue()

Constructor that creates a queue with the default size of 32.

CircularFifoQueue

public CircularFifoQueue(int size)

Constructor that creates a queue with the specified size.

Parameters:

size - the size of the queue (cannot be changed)

Throws:

IllegalArgumentException - if the size is < 1

CircularFifoQueue

public CircularFifoQueue(Collection<? extends E> coll)

Constructor that creates a queue from the specified collection. The collection size also sets the queue size.

Parameters:

coll - the collection to copy into the queue, may not be null

Throws:

NullPointerException - if the collection is null

Method Detail

size

public int size()

Returns the number of elements stored in the queue.

Specified by:

size in interface Collection<E>

Specified by:

size in class AbstractCollection<E>

Returns:

this queue's size

isEmpty

public boolean isEmpty()

Returns true if this queue is empty; false otherwise.

Specified by:

isEmpty in interface Collection<E>

Overrides:

isEmpty in class AbstractCollection<E>

Returns:

true if this queue is empty

isFull

public boolean isFull()

Returns true if this collection is full and no new elements can be added.

A CircularFifoQueue can never be full, thus this returns always false.

Specified by:

isFull in interface BoundedCollection<E>

Returns:

always returns false

isAtFullCapacity

public boolean isAtFullCapacity()

Returns true if the capacity limit of this queue has been reached, i.e. the number of elements stored in the queue equals its maximum size.

Returns:

true if the capacity limit has been reached, false otherwise

Since:

4.1

maxSize

public int maxSize()

Gets the maximum size of the collection (the bound).

Specified by:

maxSize in interface BoundedCollection<E>

Returns:

the maximum number of elements the collection can hold

clear

public void clear()

Clears this queue.

Specified by:

clear in interface Collection<E>

Overrides:

clear in class AbstractCollection<E>

add

public boolean add(E element)

Adds the given element to this queue. If the queue is full, the least recently added element is discarded so that a new element can be inserted.

Specified by:

add in interface Collection<E>

Specified by:

add in interface Queue<E>

Overrides:

add in class AbstractCollection<E>

Parameters:

element - the element to add

Returns:

true, always

Throws:

NullPointerException - if the given element is null

get

public E get(int index)

Returns the element at the specified position in this queue.

Parameters:

index - the position of the element in the queue

Returns:

the element at position index

Throws:

NoSuchElementException - if the requested position is outside the range [0, size)

offer

public boolean offer(E element)

Adds the given element to this queue. If the queue is full, the least recently added element is discarded so that a new element can be inserted.

Specified by:

offer in interface Queue<E>

Parameters:

element - the element to add

Returns:

true, always

Throws:

NullPointerException - if the given element is null

poll

public E poll()

Specified by:

poll in interface Queue<E>

element

public E element()

Specified by:

element in interface Queue<E>

peek

public E peek()

Specified by:

peek in interface Queue<E>

remove

public E remove()

Specified by:

remove in interface Queue<E>

iterator

public Iterator<E> iterator()

Returns an iterator over this queue's elements.

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in class AbstractCollection<E>

Returns:

an iterator over this queue's elements