org.apache.commons.collections
Class FastArrayList

java.lang.Object
  |
  +--java.util.AbstractCollection
        |
        +--java.util.AbstractList
              |
              +--java.util.ArrayList
                    |
                    +--org.apache.commons.collections.FastArrayList

public class FastArrayList

extends ArrayList

A customized implementation of java.util.ArrayList designed to operate in a multithreaded environment where the large majority of method calls are read-only, instead of structural changes. When operating in "fast" mode, read calls are non-synchronized and write calls perform the following steps:

• Clone the existing collection
• Perform the modification on the clone
• Replace the existing collection with the (modified) clone

When first created, objects of this class default to "slow" mode, where all accesses of any type are synchronized but no cloning takes place. This is appropriate for initially populating the collection, followed by a switch to "fast" mode (by calling setFast(true)) after initialization is complete.

NOTE: If you are creating and accessing an ArrayList only within a single thread, you should use java.util.ArrayList directly (with no synchronization), for maximum performance.

NOTE: This class is not cross-platform. Using it may cause unexpected failures on some architectures. It suffers from the same problems as the double-checked locking idiom. In particular, the instruction that clones the internal collection and the instruction that sets the internal reference to the clone can be executed or perceived out-of-order. This means that any read operation might fail unexpectedly, as it may be reading the state of the internal collection before the internal collection is fully formed. For more information on the double-checked locking idiom, see the Double-Checked Locking Idiom Is Broken Declartion.

Since:

1.0

Version:

$Revision: 1.9 $ $Date: 2002/10/12 22:15:18 $

Author:

Craig R. McClanahan

See Also:

Serialized Form

Field Summary

protected boolean	fast Are we operating in "fast" mode?
protected ArrayList	list The underlying list we are managing.

Fields inherited from class java.util.AbstractList

modCount

Constructor Summary

FastArrayList()
Construct a an empty list.

FastArrayList(Collection collection)
Construct a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

FastArrayList(int capacity)
Construct an empty list with the specified capacity.

Method Summary

void	add(int index, Object element) Insert the specified element at the specified position in this list, and shift all remaining elements up one position.
boolean	add(Object element) Appends the specified element to the end of this list.
boolean	addAll(Collection collection) Append all of the elements in the specified Collection to the end of this list, in the order that they are returned by the specified Collection's Iterator.
boolean	addAll(int index, Collection collection) Insert all of the elements in the specified Collection at the specified position in this list, and shift any previous elements upwards as needed.
void	clear() Remove all of the elements from this list.
Object	clone() Return a shallow copy of this FastArrayList instance.
boolean	contains(Object element) Return true if this list contains the specified element.
boolean	containsAll(Collection collection) Return true if this list contains all of the elements in the specified Collection.
void	ensureCapacity(int capacity) Increase the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.
boolean	equals(Object o) Compare the specified object with this list for equality.
Object	get(int index) Return the element at the specified position in the list.
boolean	getFast() Returns true if this list is operating in fast mode.
int	hashCode() Return the hash code value for this list.
int	indexOf(Object element) Search for the first occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.
boolean	isEmpty() Test if this list has no elements.
Iterator	iterator() Return an iterator over the elements in this list in proper sequence.
int	lastIndexOf(Object element) Search for the last occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.
ListIterator	listIterator() Return an iterator of the elements of this list, in proper sequence.
ListIterator	listIterator(int index) Return an iterator of the elements of this list, in proper sequence, starting at the specified position.
Object	remove(int index) Remove the element at the specified position in the list, and shift any subsequent elements down one position.
boolean	remove(Object element) Remove the first occurrence of the specified element from the list, and shift any subsequent elements down one position.
boolean	removeAll(Collection collection) Remove from this collection all of its elements that are contained in the specified collection.
boolean	retainAll(Collection collection) Remove from this collection all of its elements except those that are contained in the specified collection.
Object	set(int index, Object element) Replace the element at the specified position in this list with the specified element.
void	setFast(boolean fast) Sets whether this list will operate in fast mode.
int	size() Return the number of elements in this list.
List	subList(int fromIndex, int toIndex) Return a view of the portion of this list between fromIndex (inclusive) and toIndex (exclusive).
Object[]	toArray() Return an array containing all of the elements in this list in the correct order.
Object[]	toArray(Object[] array) Return an array containing all of the elements in this list in the correct order.
String	toString() Return a String representation of this object.
void	trimToSize() Trim the capacity of this ArrayList instance to be the list's current size.

Methods inherited from class java.util.ArrayList

removeRange

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

list

protected ArrayList list

The underlying list we are managing.

fast

protected boolean fast

Are we operating in "fast" mode?

Constructor Detail

FastArrayList

public FastArrayList()

Construct a an empty list.

FastArrayList

public FastArrayList(int capacity)

Construct an empty list with the specified capacity.

Parameters:

capacity - The initial capacity of the empty list

FastArrayList

public FastArrayList(Collection collection)

Construct a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Parameters:

collection - The collection whose elements initialize the contents of this list

Method Detail

getFast

public boolean getFast()

Returns true if this list is operating in fast mode.

Returns:

true if this list is operating in fast mode

setFast

public void setFast(boolean fast)

Sets whether this list will operate in fast mode.

Parameters:

fast - true if the list should operate in fast mode

add

public boolean add(Object element)

Appends the specified element to the end of this list.

Overrides:

add in class ArrayList

Parameters:

element - The element to be appended

add

public void add(int index,
                Object element)

Insert the specified element at the specified position in this list, and shift all remaining elements up one position.

Overrides:

add in class ArrayList

Parameters:

index - Index at which to insert this element

element - The element to be inserted

Throws:

IndexOutOfBoundsException - if the index is out of range

addAll

public boolean addAll(Collection collection)

Append all of the elements in the specified Collection to the end of this list, in the order that they are returned by the specified Collection's Iterator.

Overrides:

addAll in class ArrayList

Parameters:

collection - The collection to be appended

addAll

public boolean addAll(int index,
                      Collection collection)

Insert all of the elements in the specified Collection at the specified position in this list, and shift any previous elements upwards as needed.

Overrides:

addAll in class ArrayList

Parameters:

index - Index at which insertion takes place

collection - The collection to be added

Throws:

IndexOutOfBoundsException - if the index is out of range

clear

public void clear()

Remove all of the elements from this list. The list will be empty after this call returns.

Overrides:

clear in class ArrayList

Throws:

UnsupportedOperationException - if clear() is not supported by this list

clone

public Object clone()

Return a shallow copy of this FastArrayList instance. The elements themselves are not copied.

Overrides:

clone in class ArrayList

contains

public boolean contains(Object element)

Return true if this list contains the specified element.

Overrides:

contains in class ArrayList

Parameters:

element - The element to test for

containsAll

public boolean containsAll(Collection collection)

Return true if this list contains all of the elements in the specified Collection.

Overrides:

containsAll in class AbstractCollection

Parameters:

collection - Collection whose elements are to be checked

ensureCapacity

public void ensureCapacity(int capacity)

Increase the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.

Overrides:

ensureCapacity in class ArrayList

Parameters:

capacity - The new minimum capacity

equals

public boolean equals(Object o)

Compare the specified object with this list for equality. This implementation uses exactly the code that is used to define the list equals function in the documentation for the List.equals method.

Overrides:

equals in class AbstractList

Parameters:

o - Object to be compared to this list

get

public Object get(int index)

Return the element at the specified position in the list.

Overrides:

get in class ArrayList

Parameters:

index - The index of the element to return

Throws:

IndexOutOfBoundsException - if the index is out of range

hashCode

public int hashCode()

Return the hash code value for this list. This implementation uses exactly the code that is used to define the list hash function in the documentation for the List.hashCode method.

Overrides:

hashCode in class AbstractList

indexOf

public int indexOf(Object element)

Search for the first occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.

Overrides:

indexOf in class ArrayList

Parameters:

element - The element to search for

isEmpty

public boolean isEmpty()

Test if this list has no elements.

Overrides:

isEmpty in class ArrayList

iterator

public Iterator iterator()

Return an iterator over the elements in this list in proper sequence.

IMPLEMENTATION NOTE - If the list is operating in fast mode, an Iterator is returned, and a structural modification to the list is made, then the Iterator will continue over the previous contents of the list (at the time that the Iterator was created), rather than failing due to concurrent modifications.

Overrides:

iterator in class AbstractList

lastIndexOf

public int lastIndexOf(Object element)

Search for the last occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.

Overrides:

lastIndexOf in class ArrayList

Parameters:

element - The element to search for

listIterator

public ListIterator listIterator()

Return an iterator of the elements of this list, in proper sequence. See the implementation note on iterator().

Overrides:

listIterator in class AbstractList

listIterator

public ListIterator listIterator(int index)

Return an iterator of the elements of this list, in proper sequence, starting at the specified position. See the implementation note on iterator().

Overrides:

listIterator in class AbstractList

Parameters:

index - The starting position of the iterator to return

Throws:

IndexOutOfBoundsException - if the index is out of range

remove

public Object remove(int index)

Remove the element at the specified position in the list, and shift any subsequent elements down one position.

Overrides:

remove in class ArrayList

Parameters:

index - Index of the element to be removed

Throws:

IndexOutOfBoundsException - if the index is out of range

remove

public boolean remove(Object element)

Remove the first occurrence of the specified element from the list, and shift any subsequent elements down one position.

Overrides:

remove in class AbstractCollection

Parameters:

element - Element to be removed

removeAll

public boolean removeAll(Collection collection)

Remove from this collection all of its elements that are contained in the specified collection.

Overrides:

removeAll in class AbstractCollection

Parameters:

collection - Collection containing elements to be removed

Throws:

UnsupportedOperationException - if this optional operation is not supported by this list

retainAll

public boolean retainAll(Collection collection)

Remove from this collection all of its elements except those that are contained in the specified collection.

Overrides:

retainAll in class AbstractCollection

Parameters:

collection - Collection containing elements to be retained

Throws:

UnsupportedOperationException - if this optional operation is not supported by this list

set

public Object set(int index,
                  Object element)

Replace the element at the specified position in this list with the specified element. Returns the previous object at that position.

IMPLEMENTATION NOTE - This operation is specifically documented to not be a structural change, so it is safe to be performed without cloning.

Overrides:

set in class ArrayList

Parameters:

index - Index of the element to replace

element - The new element to be stored

Throws:

IndexOutOfBoundsException - if the index is out of range

size

public int size()

Return the number of elements in this list.

Overrides:

size in class ArrayList

subList

public List subList(int fromIndex,
                    int toIndex)

Return a view of the portion of this list between fromIndex (inclusive) and toIndex (exclusive). The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list. The returned list supports all of the optional list operations supported by this list.

Overrides:

subList in class AbstractList

Parameters:

fromIndex - The starting index of the sublist view

toIndex - The index after the end of the sublist view

Throws:

IndexOutOfBoundsException - if an index is out of range

toArray

public Object[] toArray()

Return an array containing all of the elements in this list in the correct order.

Overrides:

toArray in class ArrayList

toArray

public Object[] toArray(Object[] array)

Return an array containing all of the elements in this list in the correct order. The runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array, and the size of this list.

Overrides:

toArray in class ArrayList

Parameters:

array - Array defining the element type of the returned list

Throws:

ArrayStoreException - if the runtime type of array is not a supertype of the runtime type of every element in this list

toString

public String toString()

Return a String representation of this object.

Overrides:

toString in class AbstractCollection

trimToSize

public void trimToSize()

Trim the capacity of this ArrayList instance to be the list's current size. An application can use this operation to minimize the storage of an ArrayList instance.

Overrides:

trimToSize in class ArrayList