org.jamesframework.core.util

Class FastLimitedQueue<E>

java.lang.Object

org.jamesframework.core.util.FastLimitedQueue<E>

Type Parameters:

E - type of contained elements

public class FastLimitedQueue<E>
extends Object

A fast queue with limited size that replaces the least recently added items if it is full, and which never contains duplicates of the same item. The implementation uses a combination of a queue (to maintain addition order) and a hash set (for fast lookup of elements).

Author:

Herman De Beukelaer

Constructor Summary

Constructors

Constructor and Description
FastLimitedQueue(int sizeLimit) Creat a new instance with given size limit.

Method Summary

Modifier and Type	Method and Description
boolean	add(E e) Add an element at the tail of the queue, replacing the least recently added item if the queue is full.
boolean	addAll(Collection<E> items) Add the given collection of items.
void	clear() Clear the queue.
boolean	contains(E e) Checks whether the given item is contained in the queue.
E	remove() Retrieves and removes the head of the queue, or returns null if the queue is empty.
int	size() Get the number of items contained in the queue.
int	sizeLimit() Get the size limit of the queue.

Methods inherited from class java.lang.Object

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

Constructor Detail

FastLimitedQueue

public FastLimitedQueue(int sizeLimit)

Creat a new instance with given size limit. The specified size limit is required to be strictly positive.

Parameters:

sizeLimit - size limit of the queue, required to be strictly positive

Throws:

IllegalArgumentException - if size is not strictly positive

Method Detail

add

public boolean add(E e)

Add an element at the tail of the queue, replacing the least recently added item if the queue is full. The item is only added to the queue if it is not already contained. Runs in constant time, assuming the hash function disperses the elements properly among the buckets of the underlying hash set.

Parameters:

e - element to add at the tail of the queue, if not already contained in the queue

Returns:

true if the given item was not yet contained in the queue

addAll

public boolean addAll(Collection<E> items)

Add the given collection of items. Only those items which are not yet contained in the queue are added, in the order of iteration through the given collection. Runs in linear time, assuming the hash function disperses the elements properly among the buckets of the underlying hash set.

Parameters:

items - items to add to the queue

Returns:

true if the queue is modified, i.e. if at least one new item has been added

remove

public E remove()

Retrieves and removes the head of the queue, or returns null if the queue is empty. The head of the queue corresponds to the least recently added item (if any).

Returns:

head of the queue, null if queue is empty

contains

public boolean contains(E e)

Checks whether the given item is contained in the queue. Runs in constant time, assuming the hash function disperses the elements properly among the buckets of the underlying hash set.

Parameters:

e - given item

Returns:

true if e is contained in the queue

size

public int size()

Get the number of items contained in the queue.

Returns:

queue size

sizeLimit

public int sizeLimit()

Get the size limit of the queue.

Returns:

queue size limit

clear

public void clear()

Clear the queue.