EDU.oswego.cs.dl.util.concurrent
public class CopyOnWriteArrayList extends Object implements List, Cloneable, Serializable
This is ordinarily too costly, but it becomes attractive when traversal operations vastly overwhelm mutations, and, especially, when you cannot or don't want to synchronize traversals, yet need to preclude interference among concurrent threads. The 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. (The iterator will not traverse elements added or changed since the iterator was created, but usually this is a desirable feature.)
As much code and documentation as possible was shamelessly copied from java.util.ArrayList (Thanks, Josh!), with the intent of preserving all semantics of ArrayList except for the copy-on-write property. (The java.util collection code could not be subclassed here since all of the existing collection classes assume elementwise mutability.)
Because of the copy-on-write policy, some one-by-one mutative operations in the java.util.Arrays and java.util.Collections classes are so time/space intensive as to never be worth calling (except perhaps as benchmarks for garbage collectors :-).
Three methods are supported in addition to those described in List and ArrayList. The addIfAbsent and addAllAbsent methods provide Set semantics for add, and are used in CopyOnWriteArraySet. However, they can also be used directly from this List version. The copyIn method (and a constructor that invokes it) allow you to copy in an initial array to use. This method can be useful when you first want to perform many operations on a plain array, and then make a copy available for use through the collection API.
Due to their strict read-only nature, element-changing operations on iterators (remove, set, and add) are not supported. These are the only methods throwing UnsupportedOperationException.
Nested Class Summary | |
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protected static class | CopyOnWriteArrayList.COWIterator |
protected static class | CopyOnWriteArrayList.COWSubList |
Field Summary | |
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protected Object[] | array_
The held array. |
Constructor Summary | |
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CopyOnWriteArrayList()
Constructs an empty list
| |
CopyOnWriteArrayList(Collection c)
Constructs an list containing the elements of the specified
Collection, in the order they are returned by the Collection's
iterator. | |
CopyOnWriteArrayList(Object[] toCopyIn)
Create a new CopyOnWriteArrayList holding a copy of given array |
Method Summary | |
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boolean | add(Object element)
Appends the specified element to the end of this list.
|
void | add(int index, Object element)
Inserts the specified element at the specified position in this
list. |
boolean | addAll(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, Collection c)
Inserts all of the elements in the specified Collection into this
list, starting at the specified position. |
int | addAllAbsent(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(Object element)
Append the element if not present.
|
protected Object[] | array()
Accessor to the array intended to be called from
within unsynchronized read-only methods
|
void | clear()
Removes all of the elements from this list.
|
Object | clone()
Returns a shallow copy of this list. |
boolean | contains(Object elem)
Returns true if this list contains the specified element.
|
boolean | containsAll(Collection c)
Returns true if this Collection contains all of the elements in the
specified Collection.
|
void | copyIn(Object[] toCopyIn, int first, int n)
Replace the held array with a copy of the n
elements of the provided array, starting at position first .
|
boolean | equals(Object o)
Compares the specified Object with this List for equality. |
Object | get(int index)
Returns the element at the specified position in this list.
|
int | hashCode()
Returns the hash code value for this List.
|
int | indexOf(Object elem)
Searches for the first occurence of the given argument, testing
for equality using the equals method.
|
protected static int | indexOf(Object elem, Object[] elementData, int len)
static version allows repeated call without needed
to grab lock for array each time
|
int | indexOf(Object elem, int index)
Searches for the first occurence of the given argument, beginning
the search at index , and testing for equality using
the equals method.
|
boolean | isEmpty()
Tests if this list has no components.
|
Iterator | iterator()
Returns an Iterator over the elements contained in this collection.
|
int | lastIndexOf(Object elem)
Returns the index of the last occurrence of the specified object in
this list.
|
protected static int | lastIndexOf(Object elem, Object[] elementData, int len) |
int | lastIndexOf(Object elem, int index)
Searches backwards for the specified object, starting from the
specified index, and returns an index to it.
|
ListIterator | listIterator()
Returns an Iterator of the elements in this List (in proper sequence).
|
ListIterator | listIterator(int index)
Returns a ListIterator of the elements in this List (in proper
sequence), starting at the specified position in the List. |
protected void | rangeCheck(int index, int length)
Check if the given index is in range. |
Object | remove(int index)
Removes the element at the specified position in this list.
|
boolean | remove(Object element)
Removes a single instance of the specified element from this Collection,
if it is present (optional operation). |
boolean | removeAll(Collection c)
Removes from this Collection all of its elements that are contained in
the specified Collection. |
void | removeRange(int fromIndex, int toIndex)
Removes from this List all of the elements whose index is between
fromIndex, inclusive and toIndex, exclusive. |
boolean | retainAll(Collection c)
Retains only the elements in this Collection that are contained in the
specified Collection (optional operation). |
Object | set(int index, Object element)
Replaces the element at the specified position in this list with
the specified element.
|
int | size()
Returns the number of components in this list.
|
List | subList(int fromIndex, int toIndex)
Returns a view of the portion of this List between fromIndex,
inclusive, and toIndex, exclusive. |
Object[] | toArray()
Returns an array containing all of the elements in this list
in the correct order. |
Object[] | toArray(Object[] a)
Returns an array containing all of the elements in this list in the
correct order. |
String | toString()
Returns a string representation of this Collection, containing
the String representation of each element. |
Parameters: toCopyIn the array. A copy of this array is used as the internal array.
Parameters: element element to be appended to this list.
Returns: true (as per the general contract of Collection.add).
Parameters: index index at which the specified element is to be inserted. element element to be inserted.
Throws: IndexOutOfBoundsException index is out of range (index < 0 || index > size()).
Parameters: c elements to be inserted into this list.
Parameters: index index at which to insert first element from the specified collection. c elements to be inserted into this list.
Throws: IndexOutOfBoundsException index out of range (index < 0 || index > size()).
Parameters: c elements to be added into this list.
Returns: the number of elements added
Parameters: element element to be added to this Collection, if absent.
Returns: true if added
Returns: a clone of this list.
Parameters: o element whose presence in this List is to be tested.
This implementation iterates over the specified Collection, checking each element returned by the Iterator in turn to see if it's contained in this Collection. If all elements are so contained true is returned, otherwise false.
n
elements of the provided array, starting at position first
.
To copy an entire array, call with arguments (array, 0, array.length).Parameters: toCopyIn the array. A copy of the indicated elements of this array is used as the internal array. first The index of first position of the array to start copying from. n the number of elements to copy. This will be the new size of the list.
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.
This implementation first checks if the specified object is this List. If so, it returns true; if not, it checks if the specified object is a List. If not, it returns false; if so, it iterates over both lists, comparing corresponding pairs of elements. If any comparison returns false, this method returns false. If either Iterator runs out of elements before before the other it returns false (as the Lists are of unequal length); otherwise it returns true when the iterations complete.
Parameters: o the Object to be compared for equality with this List.
Returns: true if the specified Object is equal to this List.
Parameters: index index of element to return.
Throws: IndexOutOfBoundsException index is out of range (index < 0 || index >= size()).
This implementation uses exactly the code that is used to define the List hash function in the documentation for List.hashCode.
equals
method.
Parameters: elem an object.
Returns: the index of the first occurrence of the argument in this
list; returns -1
if the object is not found.
See Also: Object#equals(Object)
index
, and testing for equality using
the equals
method.
Parameters: elem an object. index the index to start searching from.
Returns: the index of the first occurrence of the object argument in
this List at position index
or later in the
List; returns -1
if the object is not found.
See Also: Object#equals(Object)
Returns: true
if this list has no components;
false
otherwise.
remove
method.Parameters: elem the desired component.
Returns: the index of the last occurrence of the specified object in this list; returns -1 if the object is not found.
Parameters: elem the desired component. index the index to start searching from.
Returns: the index of the last occurrence of the specified object in this List at position less than index in the List; -1 if the object is not found.
remove
, set
,
or add
methods.
Parameters: index index of first element to be returned from the ListIterator (by a call to getNext).
Throws: IndexOutOfBoundsException index is out of range (index < 0 || index > size()).
Parameters: index the index of the element to removed.
Throws: IndexOutOfBoundsException index out of range (index < 0 || index >= size()).
e
such that (o==null ? e==null :
o.equals(e))
, if the Collection contains one or more such
elements. Returns true if the Collection contained the specified
element (or equivalently, if the Collection changed as a result of the
call).
Parameters: element element to be removed from this Collection, if present.
Returns: true if the Collection changed as a result of the call.
Returns: true if this Collection changed as a result of the call.
Parameters: fromIndex index of first element to be removed. fromIndex index after last element to be removed.
Throws: IndexOutOfBoundsException fromIndex or toIndex out of range (fromIndex < 0 || fromIndex >= size() || toIndex > size() || toIndex < fromIndex).
Returns: true if this Collection changed as a result of the call.
Parameters: index index of element to replace. element element to be stored at the specified position.
Returns: the element previously at the specified position.
Throws: IndexOutOfBoundsException index out of range (index < 0 || index >= size()).
Returns: the number of components in this list.
Parameters: fromIndex low endpoint (inclusive) of the subList. toKey high endpoint (exclusive) of the subList.
Returns: a view of the specified range within this List.
Throws: IndexOutOfBoundsException Illegal endpoint index value (fromIndex < 0 || toIndex > size || fromIndex > toIndex).
If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the collection is set to null. This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.
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 the elements of the list.
Throws: ArrayStoreException the runtime type of a is not a supertype of the runtime type of every element in this list.