Java Doc for CopyOnWriteArraySet.java in  » 6.0-JDK-Core » Collections-Jar-Zip-Logging-regex » java » util » concurrent » Java Source Code / Java DocumentationJava Source Code and Java Documentation

• 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.
See Also:   CopyOnWriteArrayList
since:
   1.5
author:
   Doug Lea<
Parameters:
  E - > the type of elements held in this collection

The returned iterator provides a snapshot of the state of the set when the iterator was constructed.

The returned array will be "safe" in that no references to it are maintained by 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.

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. an iterator over the elements in this set

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. an array containing all the elements in 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 CopyOnWriteArraySet.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]);