prefuse.util.collections
Class CopyOnWriteArrayList

java.lang.Object
  prefuse.util.collections.CopyOnWriteArrayList

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.lang.Iterable, java.util.Collection, java.util.List, java.util.RandomAccess

public class CopyOnWriteArrayList
extends java.lang.Object
implements java.util.List, java.util.RandomAccess, java.lang.Cloneable, java.io.Serializable

A thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array.

This is ordinarily too costly, but may be more efficient than alternatives when traversal operations vastly outnumber mutations, and is useful when you cannot or don't want to synchronize traversals, yet need to preclude interference among concurrent threads. The "snapshot" style iterator method uses a reference to the state of the array at the point that the iterator was created. This array never changes during the lifetime of the iterator, so interference is impossible and the iterator is guaranteed not to throw ConcurrentModificationException. The iterator will not reflect additions, removals, or changes to the list since the iterator was created. Element-changing operations on iterators themselves (remove, set, and add) are not supported. These methods throw UnsupportedOperationException.

All elements are permitted, including null.

This class is a member of the Java Collections Framework.

Since:

1.5

Author:

Doug Lea

See Also:

Serialized Form

Constructor Summary

CopyOnWriteArrayList()
Creates an empty list.

CopyOnWriteArrayList(java.util.Collection c)
Creates a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

CopyOnWriteArrayList(java.lang.Object[] toCopyIn)
Creates a list holding a copy of the given array.

Method Summary

void	add(int index, java.lang.Object element) Inserts the specified element at the specified position in this list.
boolean	add(java.lang.Object e) Appends the specified element to the end of this list.
boolean	addAll(java.util.Collection c) Appends 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, java.util.Collection c) Inserts all of the elements in the specified collection into this list, starting at the specified position.
int	addAllAbsent(java.util.Collection c) Appends all of the elements in the specified collection that are not already contained in this list, to the end of this list, in the order that they are returned by the specified collection's iterator.
boolean	addIfAbsent(java.lang.Object e) Append the element if not present.
void	clear() Removes all of the elements from this list.
java.lang.Object	clone() Returns a shallow copy of this list.
boolean	contains(java.lang.Object o) Returns true if this list contains the specified element.
boolean	containsAll(java.util.Collection c) Returns true if this list contains all of the elements of the specified collection.
boolean	equals(java.lang.Object o) Compares the specified object with this list for equality.
java.lang.Object	get(int index)
java.lang.Object[]	getArray() This has been made public to support more efficient iteration.
int	hashCode() Returns the hash code value for this list.
int	indexOf(java.lang.Object o)
int	indexOf(java.lang.Object e, int index) Returns the index of the first occurrence of the specified element in this list, searching forwards from index, or returns -1 if the element is not found.
boolean	isEmpty() Returns true if this list contains no elements.
java.util.Iterator	iterator() Returns an iterator over the elements in this list in proper sequence.
int	lastIndexOf(java.lang.Object o)
int	lastIndexOf(java.lang.Object e, int index) Returns the index of the last occurrence of the specified element in this list, searching backwards from index, or returns -1 if the element is not found.
java.util.ListIterator	listIterator() The returned iterator provides a snapshot of the state of the list when the iterator was constructed.
java.util.ListIterator	listIterator(int index) The list iterator returned by this implementation will throw an UnsupportedOperationException in its remove, set and add methods.
java.lang.Object	remove(int index) Removes the element at the specified position in this list.
boolean	remove(java.lang.Object o) Removes the first occurrence of the specified element from this list, if it is present.
boolean	removeAll(java.util.Collection c) Removes from this list all of its elements that are contained in the specified collection.
boolean	retainAll(java.util.Collection c) Retains only the elements in this list that are contained in the specified collection.
java.lang.Object	set(int index, java.lang.Object element) Replaces the element at the specified position in this list with the specified element.
int	size() Returns the number of elements in this list.
java.util.List	subList(int fromIndex, int toIndex) Returns a view of the portion of this list between fromIndex, inclusive, and toIndex, exclusive.
java.lang.Object[]	toArray() Returns an array containing all of the elements in this list in proper sequence (from first to last element).
java.lang.Object[]	toArray(java.lang.Object[] a) Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.
java.lang.String	toString() Returns a string representation of this list, containing the String representation of each element.

Methods inherited from class java.lang.Object

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

Constructor Detail

CopyOnWriteArrayList

public CopyOnWriteArrayList()

Creates an empty list.

CopyOnWriteArrayList

public CopyOnWriteArrayList(java.util.Collection c)

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

Parameters:

c - the collection of initially held elements

Throws:

java.lang.NullPointerException - if the specified collection is null

CopyOnWriteArrayList

public CopyOnWriteArrayList(java.lang.Object[] toCopyIn)

Creates a list holding a copy of the given array.

Parameters:

toCopyIn - the array (a copy of this array is used as the internal array)

Throws:

java.lang.NullPointerException - if the specified array is null

Method Detail

getArray

public java.lang.Object[] getArray()

This has been made public to support more efficient iteration. DO NOT MODIFY this array upon getting it. Otherwise you risk wreaking havoc on your list. In fact, if you are not the author of this comment, you probably shouldn't use it at all.

Returns:

this lists internal array

size

public int size()

Returns the number of elements in this list.

Specified by:

size in interface java.util.Collection

Specified by:

size in interface java.util.List

Returns:

the number of elements in this list

isEmpty

public boolean isEmpty()

Returns true if this list contains no elements.

Specified by:

isEmpty in interface java.util.Collection

Specified by:

isEmpty in interface java.util.List

Returns:

true if this list contains no elements

contains

public boolean contains(java.lang.Object o)

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

Specified by:

contains in interface java.util.Collection

Specified by:

contains in interface java.util.List

Parameters:

o - element whose presence in this list is to be tested

Returns:

true if this list contains the specified element

indexOf

public int indexOf(java.lang.Object o)

Specified by:

indexOf in interface java.util.List

indexOf

public int indexOf(java.lang.Object e,
                   int index)

Returns the index of the first occurrence of the specified element in this list, searching forwards from index, or returns -1 if the element is not found. More formally, returns the lowest index i such that (i >= index && (e==null ? get(i)==null : e.equals(get(i)))), or -1 if there is no such index.

Parameters:

e - element to search for

index - index to start searching from

Returns:

the index of the first occurrence of the element in this list at position index or later in the list; -1 if the element is not found.

Throws:

java.lang.IndexOutOfBoundsException - if the specified index is negative

lastIndexOf

public int lastIndexOf(java.lang.Object o)

Specified by:

lastIndexOf in interface java.util.List

lastIndexOf

public int lastIndexOf(java.lang.Object e,
                       int index)

Returns the index of the last occurrence of the specified element in this list, searching backwards from index, or returns -1 if the element is not found. More formally, returns the highest index i such that (i <= index && (e==null ? get(i)==null : e.equals(get(i)))), or -1 if there is no such index.

Parameters:

e - element to search for

index - index to start searching backwards from

Returns:

the index of the last occurrence of the element at position less than or equal to index in this list; -1 if the element is not found.

Throws:

java.lang.IndexOutOfBoundsException - if the specified index is greater than or equal to the current size of this list

clone

public java.lang.Object clone()

Returns a shallow copy of this list. (The elements themselves are not copied.)

Overrides:

clone in class java.lang.Object

Returns:

a clone of this list

toArray

public java.lang.Object[] toArray()

Returns an array containing all of the elements in this list in proper sequence (from first to last element).

The returned array will be "safe" in that no references to it are maintained by this list. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface java.util.Collection

Specified by:

toArray in interface java.util.List

Returns:

an array containing all the elements in this list

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)

Returns an array containing all of the elements in this list in proper sequence (from first to last element); 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.

If this list fits in the specified array with room to spare (i.e., the array has more elements than this list), the element in the array immediately following the end of the list is set to null. (This is useful in determining the length of this list only if the caller knows that this list does not contain any null elements.)

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a list known to contain only strings. The following code can be used to dump the list into a newly allocated array of String:

     String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

Specified by:

toArray in interface java.util.Collection

Specified by:

toArray in interface java.util.List

Parameters:

a - the array into which the elements of the list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Returns:

an array containing all the elements in this list

Throws:

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

java.lang.NullPointerException - if the specified array is null

get

public java.lang.Object get(int index)

Specified by:

get in interface java.util.List

Throws:

java.lang.IndexOutOfBoundsException

set

public java.lang.Object set(int index,
                            java.lang.Object element)

Replaces the element at the specified position in this list with the specified element.

Specified by:

set in interface java.util.List

Throws:

java.lang.IndexOutOfBoundsException

add

public boolean add(java.lang.Object e)

Appends the specified element to the end of this list.

Specified by:

add in interface java.util.Collection

Specified by:

add in interface java.util.List

Parameters:

e - element to be appended to this list

Returns:

true (as per the spec for Collection.add(E))

add

public void add(int index,
                java.lang.Object element)

Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

Specified by:

add in interface java.util.List

Throws:

java.lang.IndexOutOfBoundsException

remove

public java.lang.Object remove(int index)

Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices). Returns the element that was removed from the list.

Specified by:

remove in interface java.util.List

Throws:

java.lang.IndexOutOfBoundsException

remove

public boolean remove(java.lang.Object o)

Removes the first occurrence of the specified element from this list, if it is present. If this list does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).

Specified by:

remove in interface java.util.Collection

Specified by:

remove in interface java.util.List

Parameters:

o - element to be removed from this list, if present

Returns:

true if this list contained the specified element

addIfAbsent

public boolean addIfAbsent(java.lang.Object e)

Append the element if not present.

Parameters:

e - element to be added to this list, if absent

Returns:

true if the element was added

containsAll

public boolean containsAll(java.util.Collection c)

Returns true if this list contains all of the elements of the specified collection.

Specified by:

containsAll in interface java.util.Collection

Specified by:

containsAll in interface java.util.List

Parameters:

c - collection to be checked for containment in this list

Returns:

true if this list contains all of the elements of the specified collection

Throws:

java.lang.NullPointerException - if the specified collection is null

See Also:

contains(Object)

removeAll

public boolean removeAll(java.util.Collection c)

Removes from this list all of its elements that are contained in the specified collection. This is a particularly expensive operation in this class because of the need for an internal temporary array.

Specified by:

removeAll in interface java.util.Collection

Specified by:

removeAll in interface java.util.List

Parameters:

c - collection containing elements to be removed from this list

Returns:

true if this list changed as a result of the call

Throws:

java.lang.ClassCastException - if the class of an element of this list is incompatible with the specified collection (optional)

java.lang.NullPointerException - if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

See Also:

remove(Object)

retainAll

public boolean retainAll(java.util.Collection c)

Retains only the elements in this list that are contained in the specified collection. In other words, removes from this list all of its elements that are not contained in the specified collection.

Specified by:

retainAll in interface java.util.Collection

Specified by:

retainAll in interface java.util.List

Parameters:

c - collection containing elements to be retained in this list

Returns:

true if this list changed as a result of the call

Throws:

java.lang.ClassCastException - if the class of an element of this list is incompatible with the specified collection (optional)

java.lang.NullPointerException - if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

See Also:

remove(Object)

addAllAbsent

public int addAllAbsent(java.util.Collection c)

Appends all of the elements in the specified collection that are not already contained in this list, to the end of this list, in the order that they are returned by the specified collection's iterator.

Parameters:

c - collection containing elements to be added to this list

Returns:

the number of elements added

Throws:

java.lang.NullPointerException - if the specified collection is null

See Also:

addIfAbsent(Object)

clear

public void clear()

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

Specified by:

clear in interface java.util.Collection

Specified by:

clear in interface java.util.List

addAll

public boolean addAll(java.util.Collection c)

Appends 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.

Specified by:

addAll in interface java.util.Collection

Specified by:

addAll in interface java.util.List

Parameters:

c - collection containing elements to be added to this list

Returns:

true if this list changed as a result of the call

Throws:

java.lang.NullPointerException - if the specified collection is null

See Also:

add(Object)

addAll

public boolean addAll(int index,
                      java.util.Collection c)

Inserts all of the elements in the specified collection into this list, starting at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in this list in the order that they are returned by the specified collection's iterator.

Specified by:

addAll in interface java.util.List

Parameters:

index - index at which to insert the first element from the specified collection

c - collection containing elements to be added to this list

Returns:

true if this list changed as a result of the call

Throws:

java.lang.IndexOutOfBoundsException

java.lang.NullPointerException - if the specified collection is null

See Also:

add(int,Object)

toString

public java.lang.String toString()

Returns a string representation of this list, containing the String representation of each element.

Overrides:

toString in class java.lang.Object

equals

public boolean equals(java.lang.Object o)

Compares the specified object with this list for equality. Returns true if and only if the specified object is also a List, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elements e1 and e2 are equal if (e1==null ? e2==null : e1.equals(e2)).) In other words, two lists are defined to be equal if they contain the same elements in the same order.

Specified by:

equals in interface java.util.Collection

Specified by:

equals in interface java.util.List

Overrides:

equals in class java.lang.Object

Parameters:

o - the object to be compared for equality with this list

Returns:

true if the specified object is equal to this list

hashCode

public int hashCode()

Returns the hash code value for this list.

This implementation uses the definition in List.hashCode().

Specified by:

hashCode in interface java.util.Collection

Specified by:

hashCode in interface java.util.List

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code value for this list

iterator

public java.util.Iterator iterator()

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

The returned iterator provides a snapshot of the state of the list when the iterator was constructed. No synchronization is needed while traversing the iterator. The iterator does NOT support the remove method.

Specified by:

iterator in interface java.lang.Iterable

Specified by:

iterator in interface java.util.Collection

Specified by:

iterator in interface java.util.List

Returns:

an iterator over the elements in this list in proper sequence

listIterator

public java.util.ListIterator listIterator()

The returned iterator provides a snapshot of the state of the list when the iterator was constructed. No synchronization is needed while traversing the iterator. The iterator does NOT support the remove, set or add methods.

Specified by:

listIterator in interface java.util.List

listIterator

public java.util.ListIterator listIterator(int index)

The list iterator returned by this implementation will throw an UnsupportedOperationException in its remove, set and add methods.

Specified by:

listIterator in interface java.util.List

Throws:

java.lang.IndexOutOfBoundsException

subList

public java.util.List subList(int fromIndex,
                              int toIndex)

Returns a view of the portion of this list between fromIndex, inclusive, and toIndex, exclusive. The returned list is backed by this list, so changes in the returned list are reflected in this list, and vice-versa. While mutative operations are supported, they are probably not very useful for CopyOnWriteArrayLists.

The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)

Specified by:

subList in interface java.util.List

Parameters:

fromIndex - low endpoint (inclusive) of the subList

toIndex - high endpoint (exclusive) of the subList

Returns:

a view of the specified range within this list

Throws:

java.lang.IndexOutOfBoundsException