File	Doc	Category	Size	Date	Package
CopyOnWriteArraySet.java	API Doc	Java SE 6 API	14054	Tue Jun 10 00:25:56 BST 2008	java.util.concurrent

CopyOnWriteArraySet

• java.lang.Object
  • java.util.AbstractCollection
    • java.util.AbstractSet

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();
}
}

Fields Summary
private static final long	serialVersionUID
private final CopyOnWriteArrayList	al

Constructors Summary
public CopyOnWriteArraySet() Creates an empty set. al = new CopyOnWriteArrayList<E>();
public CopyOnWriteArraySet(Collection c) Creates a set containing all of the elements of the specified collection. param c the collection of elements to initially contain throws NullPointerException if the specified collection is null al = new CopyOnWriteArrayList<E>(); al.addAllAbsent(c);

Methods Summary
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. param e element to be added to this set return true if this set did not already contain the specified element return al.addIfAbsent(e);
public boolean	addAll(java.util.Collection 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. param c collection containing elements to be added to this set return true if this set changed as a result of the call throws NullPointerException if the specified collection is null see #add(Object) return al.addAllAbsent(c) > 0;
public void	clear() Removes all of the elements from this set. The set will be empty after this call returns. al.clear();
public boolean	contains(java.lang.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)). param o element whose presence in this set is to be tested return true if this set contains the specified element return al.contains(o);
public boolean	containsAll(java.util.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. param c collection to be checked for containment in this set return true if this set contains all of the elements of the specified collection throws NullPointerException if the specified collection is null see #contains(Object) return al.containsAll(c);
private static boolean	eq(java.lang.Object o1, java.lang.Object o2) Test for equality, coping with nulls. return (o1 == null ? o2 == null : o1.equals(o2));
public boolean	equals(java.lang.Object o) Compares the specified object with this set for equality. Returns {@code true} if the specified object is the same object as this object, or if it is also a {@link Set} and the elements returned by an {@linkplain List#iterator() 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 {@code e1} returned by the iterator over the specified set, there is an element {@code e2} returned by the iterator over this set such that {@code (e1==null ? e2==null : e1.equals(e2))}. param o object to be compared for equality with this set return {@code true} if the specified object is equal to this set if (o == this) return true; if (!(o instanceof Set)) return false; Set<?> set = (Set<?>)(o); Iterator<?> it = set.iterator(); // Uses O(n^2) algorithm that is only appropriate // for small sets, which CopyOnWriteArraySets should be. // Use a single snapshot of underlying array Object[] elements = al.getArray(); int len = elements.length; // Mark matched elements to avoid re-checking boolean[] matched = new boolean[len]; int k = 0; outer: while (it.hasNext()) { if (++k > len) return false; Object x = it.next(); for (int i = 0; i < len; ++i) { if (!matched[i] && eq(x, elements[i])) { matched[i] = true; continue outer; } } return false; } return k == len;
public boolean	isEmpty() Returns true if this set contains no elements. return true if this set contains no elements return al.isEmpty();
public java.util.Iterator	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. return an iterator over the elements in this set return al.iterator();
public boolean	remove(java.lang.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.) param o object to be removed from this set, if present return true if this set contained the specified element return al.remove(o);
public boolean	removeAll(java.util.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. param c collection containing elements to be removed from this set return true if this set changed as a result of the call throws ClassCastException if the class of an element of this set is incompatible with the specified collection (optional) throws 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 see #remove(Object) return al.removeAll(c);
public boolean	retainAll(java.util.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. param c collection containing elements to be retained in this set return true if this set changed as a result of the call throws ClassCastException if the class of an element of this set is incompatible with the specified collection (optional) throws 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 see #remove(Object) return al.retainAll(c);
public int	size() Returns the number of elements in this set. return the number of elements in this set return al.size();
public java.lang.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. return an array containing all the elements in this set return al.toArray();
public 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 {@link #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(). param 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. return an array containing all the elements in this set throws ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this set throws NullPointerException if the specified array is null return al.toArray(a);