org.apache.commons.collections

Class 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:

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 Declaration.

Since: Commons Collections 1.0

Version: $Revision: 178303 $ $Date: 2005-05-24 23:39:51 +0100 (Tue, 24 May 2005) $

Author: Craig R. McClanahan Stephen Colebourne

Field Summary
protected booleanfast
Are we operating in "fast" mode?
protected ArrayListlist
The underlying list we are managing.
Constructor Summary
FastArrayList()
Construct a an empty list.
FastArrayList(int capacity)
Construct an empty list with the specified capacity.
FastArrayList(Collection collection)
Construct a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
Method Summary
booleanadd(Object element)
Appends the specified element to the end of this list.
voidadd(int index, Object element)
Insert the specified element at the specified position in this list, and shift all remaining elements up one position.
booleanaddAll(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.
booleanaddAll(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.
voidclear()
Remove all of the elements from this list.
Objectclone()
Return a shallow copy of this FastArrayList instance.
booleancontains(Object element)
Return true if this list contains the specified element.
booleancontainsAll(Collection collection)
Return true if this list contains all of the elements in the specified Collection.
voidensureCapacity(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.
booleanequals(Object o)
Compare the specified object with this list for equality.
Objectget(int index)
Return the element at the specified position in the list.
booleangetFast()
Returns true if this list is operating in fast mode.
inthashCode()
Return the hash code value for this list.
intindexOf(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.
booleanisEmpty()
Test if this list has no elements.
Iteratoriterator()
Return an iterator over the elements in this list in proper sequence.
intlastIndexOf(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.
ListIteratorlistIterator()
Return an iterator of the elements of this list, in proper sequence.
ListIteratorlistIterator(int index)
Return an iterator of the elements of this list, in proper sequence, starting at the specified position.
Objectremove(int index)
Remove the element at the specified position in the list, and shift any subsequent elements down one position.
booleanremove(Object element)
Remove the first occurrence of the specified element from the list, and shift any subsequent elements down one position.
booleanremoveAll(Collection collection)
Remove from this collection all of its elements that are contained in the specified collection.
booleanretainAll(Collection collection)
Remove from this collection all of its elements except those that are contained in the specified collection.
Objectset(int index, Object element)
Replace the element at the specified position in this list with the specified element.
voidsetFast(boolean fast)
Sets whether this list will operate in fast mode.
intsize()
Return the number of elements in this list.
ListsubList(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.
StringtoString()
Return a String representation of this object.
voidtrimToSize()
Trim the capacity of this ArrayList instance to be the list's current size.

Field Detail

fast

protected boolean fast
Are we operating in "fast" mode?

list

protected ArrayList list
The underlying list we are managing.

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

add

public boolean add(Object element)
Appends the specified element to the end of this list.

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.

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.

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.

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.

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.

contains

public boolean contains(Object element)
Return true if this list contains the specified element.

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.

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.

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.

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.

Parameters: index The index of the element to return

Throws: IndexOutOfBoundsException if the index is out of range

getFast

public boolean getFast()
Returns true if this list is operating in fast mode.

Returns: true if this list is operating in fast mode

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.

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.

Parameters: element The element to search for

isEmpty

public boolean isEmpty()
Test if this list has no elements.

iterator

public Iterator iterator()
Return an iterator over the elements in this list in proper sequence.

Thread safety
The iterator returned is thread-safe ONLY in FAST mode. In slow mode there is no way to synchronize, or make the iterator thread-safe.

In fast mode iteration and modification may occur in parallel on different threads, however there is a restriction. Modification must be EITHER via the Iterator interface methods OR the List interface. If a mixture of modification methods is used a ConcurrentModificationException is thrown from the iterator modification method. If the List modification methods are used the changes are NOT visible in the iterator (it shows the list contents at the time the iterator was created).

Returns: the iterator

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.

Parameters: element The element to search for

listIterator

public ListIterator listIterator()
Return an iterator of the elements of this list, in proper sequence.

Thread safety
The iterator returned is thread-safe ONLY in FAST mode. In slow mode there is no way to synchronize, or make the iterator thread-safe.

In fast mode iteration and modification may occur in parallel on different threads, however there is a restriction. Modification must be EITHER via the Iterator interface methods OR the List interface. If a mixture of modification methods is used a ConcurrentModificationException is thrown from the iterator modification method. If the List modification methods are used the changes are NOT visible in the iterator (it shows the list contents at the time the iterator was created).

Returns: the list iterator

listIterator

public ListIterator listIterator(int index)
Return an iterator of the elements of this list, in proper sequence, starting at the specified position.

Thread safety
The iterator returned is thread-safe ONLY in FAST mode. In slow mode there is no way to synchronize, or make the iterator thread-safe.

In fast mode iteration and modification may occur in parallel on different threads, however there is a restriction. Modification must be EITHER via the Iterator interface methods OR the List interface. If a mixture of modification methods is used a ConcurrentModificationException is thrown from the iterator modification method. If the List modification methods are used the changes are NOT visible in the iterator (it shows the list contents at the time the iterator was created).

Parameters: index The starting position of the iterator to return

Returns: the list iterator

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.

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.

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.

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.

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.

Parameters: index Index of the element to replace element The new element to be stored

Throws: IndexOutOfBoundsException if the index is out of range

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

size

public int size()
Return the number of elements in this list.

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.

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.

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.

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.

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.
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