CopyOnWriteArraySet

java.lang.Object
- java.util.AbstractCollection<E>
- - java.util.AbstractSet<E>
  - - java.util.concurrent.CopyOnWriteArraySet<E>

类型参数:

E - the type of elements held in this collection

所有已实现的接口:

Serializable, Iterable<E>, Collection<E>, Set<E>
```
public class CopyOnWriteArraySet<E>
extends AbstractSet<E>
implements Serializable
```
A Set that uses an internal CopyOnWriteArrayList for all of its operations. Thus, it shares the same basic properties:
- It is best suited for applications in which set sizes generally stay small, read-only operations vastly outnumber mutative operations, and you need to prevent interference among threads during traversal.
- It is thread-safe.
- Mutative operations (add, set, remove, etc.) are expensive since they usually entail copying the entire underlying array.
- Iterators do not support the mutative remove operation.
- Traversal via iterators is fast and cannot encounter interference from other threads. Iterators rely on unchanging snapshots of the array at the time the iterators were constructed.
Sample Usage. The following code sketch uses a copy-on-write set to maintain a set of Handler objects that perform some action upon state updates.
```
 
 class Handler { void handle(); ... }

 class X {
   private final CopyOnWriteArraySet<Handler> handlers
     = new CopyOnWriteArraySet<Handler>();
   public void addHandler(Handler h) { handlers.add(h); }

   private long internalState;
   private synchronized void changeState() { internalState = ...; }

   public void update() {
     changeState();
     for (Handler handler : handlers)
       handler.handle();
   }
 }
```
This class is a member of the Java Collections Framework.
从以下版本开始:

1.5

另请参阅:

CopyOnWriteArrayList, 序列化表格

构造器概要

构造器
构造器	说明
`CopyOnWriteArraySet()`	Creates an empty set.
`CopyOnWriteArraySet(Collection<? extends E> c)`	Creates a set containing all of the elements of the specified collection.

方法概要

所有方法实例方法具体方法
限定符和类型	方法	说明
`boolean`	`add(E e)`	Adds the specified element to this set if it is not already present.
`boolean`	`addAll(Collection<? extends E> c)`	Adds all of the elements in the specified collection to this set if they're not already present.
`void`	`clear()`	Removes all of the elements from this set.
`boolean`	`contains(Object o)`	Returns `true` if this set contains the specified element.
`boolean`	`containsAll(Collection<?> c)`	Returns `true` if this set contains all of the elements of the specified collection.
`boolean`	`equals(Object o)`	Compares the specified object with this set for equality.
`void`	`forEach(Consumer<? super E> action)`	Performs the given action for each element of the `Iterable` until all elements have been processed or the action throws an exception.
`boolean`	`isEmpty()`	Returns `true` if this set contains no elements.
`Iterator<E>`	`iterator()`	Returns an iterator over the elements contained in this set in the order in which these elements were added.
`boolean`	`remove(Object o)`	Removes the specified element from this set if it is present.
`boolean`	`removeAll(Collection<?> c)`	Removes from this set all of its elements that are contained in the specified collection.
`boolean`	`removeIf(Predicate<? super E> filter)`	Removes all of the elements of this collection that satisfy the given predicate.
`boolean`	`retainAll(Collection<?> c)`	Retains only the elements in this set that are contained in the specified collection.
`int`	`size()`	Returns the number of elements in this set.
`Spliterator<E>`	`spliterator()`	Returns a `Spliterator` over the elements in this set in the order in which these elements were added.
`Object[]`	`toArray()`	Returns an array containing all of the elements in this set.
`<T> T[]`	`toArray(T[] a)`	Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.

从类继承的方法 java.util.AbstractCollection
toString

从类继承的方法 java.util.AbstractSet
hashCode

从接口继承的方法 java.util.Collection
parallelStream, stream

从类继承的方法 java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- 构造器详细资料
  - CopyOnWriteArraySet
```
public CopyOnWriteArraySet()
```
    Creates an empty set.
  - CopyOnWriteArraySet
```
public CopyOnWriteArraySet(Collection<? extends E> c)
```
    Creates a set containing all of the elements of the specified collection.
    
    参数:
    
    c - the collection of elements to initially contain
    
    抛出:
    
    NullPointerException - if the specified collection is null
- 方法详细资料
  - size
```
public int size()
```
    Returns the number of elements in this set.
    
    指定者:
    
    size 在接口中 Collection<E>
    
    指定者:
    
    size 在接口中 Set<E>
    
    指定者:
    
    size 在类中 AbstractCollection<E>
    
    返回:
    
    the number of elements in this set
  - isEmpty
```
public boolean isEmpty()
```
    Returns true if this set contains no elements.
    
    指定者:
    
    isEmpty 在接口中 Collection<E>
    
    指定者:
    
    isEmpty 在接口中 Set<E>
    
    覆盖:
    
    isEmpty 在类中 AbstractCollection<E>
    
    返回:
    
    true if this set contains no elements
  - contains
```
public boolean contains(Object o)
```
    Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that (o==null ? e==null : o.equals(e)).
    
    指定者:
    
    contains 在接口中 Collection<E>
    
    指定者:
    
    contains 在接口中 Set<E>
    
    覆盖:
    
    contains 在类中 AbstractCollection<E>
    
    参数:
    
    o - element whose presence in this set is to be tested
    
    返回:
    
    true if this set contains the specified element
  - toArray
```
public Object[] toArray()
```
    Returns an array containing all of the elements in this set. If this set makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
    The returned array will be "safe" in that no references to it are maintained by this set. (In other words, this method must allocate a new array even if this set is backed by an array). The caller is thus free to modify the returned array.
    This method acts as bridge between array-based and collection-based APIs.
    
    指定者:
    
    toArray 在接口中 Collection<E>
    
    指定者:
    
    toArray 在接口中 Set<E>
    
    覆盖:
    
    toArray 在类中 AbstractCollection<E>
    
    返回:
    
    an array containing all the elements in this set
  - toArray
```
public <T> T[] toArray(T[] a)
```
    Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array. If the set 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 set.
    If this set fits in the specified array with room to spare (i.e., the array has more elements than this set), the element in the array immediately following the end of the set is set to null. (This is useful in determining the length of this set only if the caller knows that this set does not contain any null elements.)
    If this set makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
    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 set known to contain only strings. The following code can be used to dump the set 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().
    指定者:
    
    toArray 在接口中 Collection<E>
    
    指定者:
    
    toArray 在接口中 Set<E>
    
    覆盖:
    
    toArray 在类中 AbstractCollection<E>
    
    类型参数:
    
    T - the runtime type of the array to contain the collection
    
    参数:
    
    a - the array into which the elements of this set are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
    
    返回:
    
    an array containing all the elements in this set
    
    抛出:
    
    ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this set
    
    NullPointerException - if the specified array is null
  - clear
```
public void clear()
```
    Removes all of the elements from this set. The set will be empty after this call returns.
    
    指定者:
    
    clear 在接口中 Collection<E>
    
    指定者:
    
    clear 在接口中 Set<E>
    
    覆盖:
    
    clear 在类中 AbstractCollection<E>
  - remove
```
public boolean remove(Object o)
```
    Removes the specified element from this set if it is present. More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if this set contains such an element. Returns true if this set contained the element (or equivalently, if this set changed as a result of the call). (This set will not contain the element once the call returns.)
    
    指定者:
    
    remove 在接口中 Collection<E>
    
    指定者:
    
    remove 在接口中 Set<E>
    
    覆盖:
    
    remove 在类中 AbstractCollection<E>
    
    参数:
    
    o - object to be removed from this set, if present
    
    返回:
    
    true if this set contained the specified element
  - add
```
public boolean add(E e)
```
    Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if the set contains no element e2 such that (e==null ? e2==null : e.equals(e2)). If this set already contains the element, the call leaves the set unchanged and returns false.
    
    指定者:
    
    add 在接口中 Collection<E>
    
    指定者:
    
    add 在接口中 Set<E>
    
    覆盖:
    
    add 在类中 AbstractCollection<E>
    
    参数:
    
    e - element to be added to this set
    
    返回:
    
    true if this set did not already contain the specified element
  - containsAll
```
public boolean containsAll(Collection<?> c)
```
    Returns true if this set contains all of the elements of the specified collection. If the specified collection is also a set, this method returns true if it is a subset of this set.
    
    指定者:
    
    containsAll 在接口中 Collection<E>
    
    指定者:
    
    containsAll 在接口中 Set<E>
    
    覆盖:
    
    containsAll 在类中 AbstractCollection<E>
    
    参数:
    
    c - collection to be checked for containment in this set
    
    返回:
    
    true if this set contains all of the elements of the specified collection
    
    抛出:
    
    NullPointerException - if the specified collection is null
    
    另请参阅:
    
    contains(Object)
  - addAll
```
public boolean addAll(Collection<? extends E> c)
```
    Adds all of the elements in the specified collection to this set if they're not already present. If the specified collection is also a set, the addAll operation effectively modifies this set so that its value is the union of the two sets. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress.
    
    指定者:
    
    addAll 在接口中 Collection<E>
    
    指定者:
    
    addAll 在接口中 Set<E>
    
    覆盖:
    
    addAll 在类中 AbstractCollection<E>
    
    参数:
    
    c - collection containing elements to be added to this set
    
    返回:
    
    true if this set changed as a result of the call
    
    抛出:
    
    NullPointerException - if the specified collection is null
    
    另请参阅:
    
    add(Object)
  - removeAll
```
public boolean removeAll(Collection<?> c)
```
    Removes from this set all of its elements that are contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the asymmetric set difference of the two sets.
    
    指定者:
    
    removeAll 在接口中 Collection<E>
    
    指定者:
    
    removeAll 在接口中 Set<E>
    
    覆盖:
    
    removeAll 在类中 AbstractSet<E>
    
    参数:
    
    c - collection containing elements to be removed from this set
    
    返回:
    
    true if this set changed as a result of the call
    
    抛出:
    
    ClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)
    
    NullPointerException - if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null
    
    另请参阅:
    
    remove(Object)
  - retainAll
```
public boolean retainAll(Collection<?> c)
```
    Retains only the elements in this set that are contained in the specified collection. In other words, removes from this set all of its elements that are not contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the intersection of the two sets.
    
    指定者:
    
    retainAll 在接口中 Collection<E>
    
    指定者:
    
    retainAll 在接口中 Set<E>
    
    覆盖:
    
    retainAll 在类中 AbstractCollection<E>
    
    参数:
    
    c - collection containing elements to be retained in this set
    
    返回:
    
    true if this set changed as a result of the call
    
    抛出:
    
    ClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)
    
    NullPointerException - if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null
    
    另请参阅:
    
    remove(Object)
  - iterator
```
public Iterator<E> iterator()
```
    Returns an iterator over the elements contained in this set in the order in which these elements were added.
    The returned iterator provides a snapshot of the state of the set when the iterator was constructed. No synchronization is needed while traversing the iterator. The iterator does NOT support the remove method.
    
    指定者:
    
    iterator 在接口中 Collection<E>
    
    指定者:
    
    iterator 在接口中 Iterable<E>
    
    指定者:
    
    iterator 在接口中 Set<E>
    
    指定者:
    
    iterator 在类中 AbstractCollection<E>
    
    返回:
    
    an iterator over the elements in this set
  - equals
```
public boolean equals(Object o)
```
    Compares the specified object with this set for equality. Returns true if the specified object is the same object as this object, or if it is also a Set and the elements returned by an Set#iterator() over the specified set are the same as the elements returned by an iterator over this set. More formally, the two iterators are considered to return the same elements if they return the same number of elements and for every element e1 returned by the iterator over the specified set, there is an element e2 returned by the iterator over this set such that (e1==null ? e2==null : e1.equals(e2)).
    
    指定者:
    
    equals 在接口中 Collection<E>
    
    指定者:
    
    equals 在接口中 Set<E>
    
    覆盖:
    
    equals 在类中 AbstractSet<E>
    
    参数:
    
    o - object to be compared for equality with this set
    
    返回:
    
    true if the specified object is equal to this set
    
    另请参阅:
    
    Object.hashCode(), HashMap
  - removeIf
```
public boolean removeIf(Predicate<? super E> filter)
```
    从接口复制的说明: Collection
    
    Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.
    
    指定者:
    
    removeIf 在接口中 Collection<E>
    
    参数:
    
    filter - a predicate which returns true for elements to be removed
    
    返回:
    
    true if any elements were removed
  - forEach
```
public void forEach(Consumer<? super E> action)
```
    从接口复制的说明: Iterable
    
    Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. Unless otherwise specified by the implementing class, actions are performed in the order of iteration (if an iteration order is specified). Exceptions thrown by the action are relayed to the caller.
    
    指定者:
    
    forEach 在接口中 Iterable<E>
    
    参数:
    
    action - The action to be performed for each element
  - spliterator
```
public Spliterator<E> spliterator()
```
    Returns a Spliterator over the elements in this set in the order in which these elements were added.
    The Spliterator reports Spliterator#IMMUTABLE, Spliterator#DISTINCT, Spliterator#SIZED, and Spliterator#SUBSIZED.
    The spliterator provides a snapshot of the state of the set when the spliterator was constructed. No synchronization is needed while operating on the spliterator.
    
    指定者:
    
    spliterator 在接口中 Collection<E>
    
    指定者:
    
    spliterator 在接口中 Iterable<E>
    
    指定者:
    
    spliterator 在接口中 Set<E>
    
    返回:
    
    a Spliterator over the elements in this set
    
    从以下版本开始:
    
    1.8

类 CopyOnWriteArraySet<E>

构造器概要

方法概要

从类继承的方法 java.util.AbstractCollection

从类继承的方法 java.util.AbstractSet

从接口继承的方法 java.util.Collection

从类继承的方法 java.lang.Object

构造器详细资料

CopyOnWriteArraySet

CopyOnWriteArraySet

方法详细资料

size

isEmpty

contains

toArray

toArray

clear

remove

add

containsAll

addAll

removeAll

retainAll

iterator

equals

removeIf

forEach

spliterator