Class: java.util.concurrent.CopyOnWriteArrayList<E>
- public class CopyOnWriteArrayList<E>
- implements List<E>, RandomAccess, Cloneable, Serializable
A thread-safe variant of java.util.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.
Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a CopyOnWriteArrayList happen-before actions subsequent to the access or removal of that element from the CopyOnWriteArrayList in another thread.
This class is a member of the Java Collections Framework.
Inheritance
Superclass tree:- java.lang.Object
- java.util.concurrent.CopyOnWriteArrayList
- List<E>
- RandomAccess
- Cloneable
- Serializable
- Collection<E>
- Iterable<E>
Methods
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CopyOnWriteArrayListtop
public CopyOnWriteArrayList()Creates an empty list. -
CopyOnWriteArrayListtop
public CopyOnWriteArrayList(Collection<? extends E> c)Creates a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. -
CopyOnWriteArrayListtop
public CopyOnWriteArrayList(E[] toCopyIn)Creates a list holding a copy of the given array. -
addtop
public void add(int index, E 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). -
addtop
public boolean add(E e)Appends the specified element to the end of this list.- Specified by:
- add from List<E>
- add from Collection<E>
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addAlltop
public boolean addAll(int index, Collection<? extends E> 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. -
addAlltop
public boolean addAll(Collection<? extends E> 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 from List<E>
- addAll from Collection<E>
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addAllAbsenttop
public int addAllAbsent(Collection<? extends E> 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. -
addIfAbsenttop
public boolean addIfAbsent(E e)Append the element if not present. -
cleartop
public void clear()Removes all of the elements from this list. The list will be empty after this call returns.- Specified by:
- clear from List<E>
- clear from Collection<E>
-
clonetop
public Object clone()Returns a shallow copy of this list. (The elements themselves are not copied.) -
containstop
public boolean contains(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 from List<E>
- contains from Collection<E>
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containsAlltop
public boolean containsAll(Collection<?> c)Returns true if this list contains all of the elements of the specified collection.- Specified by:
- containsAll from List<E>
- containsAll from Collection<E>
-
equalstop
public boolean equals(Object o)Compares the specified object with this list for equality. Returns true if the specified object is the same object as this object, or if it is also a java.util.List and the sequence of elements returned by an iterator over the specified list is the same as the sequence returned by an iterator over this list. The two sequences are considered to be the same if they have the same length and corresponding elements at the same position in the sequence are equal. Two elements e1 and e2 are considered equal if (e1==null ? e2==null : e1.equals(e2)). -
gettop
public E get(int index)Returns the element at the specified position in this list. -
hashCodetop
public int hashCode()Returns the hash code value for this list.This implementation uses the definition in java.util.List.hashCode().
- Specified by:
- hashCode from List<E>
- hashCode from Collection<E>
-
indexOftop
public int indexOf(Object o)Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index. -
indexOftop
public int indexOf(E 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. -
isEmptytop
public boolean isEmpty()Returns true if this list contains no elements.- Specified by:
- isEmpty from List<E>
- isEmpty from Collection<E>
-
iteratortop
public Iterator<E> 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.
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lastIndexOftop
public int lastIndexOf(Object o)Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the highest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.- Specified by:
- lastIndexOf from List<E>
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lastIndexOftop
public int lastIndexOf(E 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. -
listIteratortop
public ListIterator<E> listIterator()Returns a list 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, set or add methods.
- Specified by:
- listIterator from List<E>
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listIteratortop
public ListIterator<E> listIterator(int index)Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call to next. An initial call to previous would return the element with the specified index minus one.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 from List<E>
-
removetop
public E 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. -
removetop
public boolean remove(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 from List<E>
- remove from Collection<E>
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removeAlltop
public boolean removeAll(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 from List<E>
- removeAll from Collection<E>
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retainAlltop
public boolean retainAll(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 from List<E>
- retainAll from Collection<E>
-
settop
public E set(int index, E element)Replaces the element at the specified position in this list with the specified element. -
sizetop
public int size()Returns the number of elements in this list.- Specified by:
- size from List<E>
- size from Collection<E>
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subListtop
public List<E> 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.)
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toArraytop
public 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 from List<E>
- toArray from Collection<E>
-
toArraytop
public <T> T[] toArray(T[] a)- @SuppressWarnings(value={"unchecked"})
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 java.util.concurrent.CopyOnWriteArrayList.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 from List<E>
- toArray from Collection<E>
-
toStringtop
public String toString()Returns a string representation of this list. The string representation consists of the string representations of the list's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(java.lang.Object).