Adds the specified element to this set if it is not already present.

  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.
Returns: true if this set did not already contain the specified element
Parameters:
- e - element to be added to this set

  Adds all of the elements in the specified collection to this set if they're not already present.

  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.
Returns: true if this set changed as a result of the call
Parameters:
- c - collection containing elements to be added to this set
Throws:
- NullPointerException - if the specified collection is null
See Also: CopyOnWriteArraySet.add(Object),

  Removes all of the elements from this set.

  Removes all of the elements from this set.
The set will be empty after this call returns.

  Returns true if this set contains the specified element.

  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)).
Returns: true if this set contains the specified element
Parameters:
- o - element whose presence in this set is to be tested

  Returns true if this set contains all of the elements of the specified collection.

  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.
Returns: true if this set contains all of the elements of the specified collection
Parameters:
- c - collection to be checked for containment in this set
Throws:
- NullPointerException - if the specified collection is null
See Also: CopyOnWriteArraySet.contains(Object),

  Compares the specified object with this set for equality.

  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 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)).
Returns: {@code true} if the specified object is equal to this set
Parameters:
- o - object to be compared for equality with this set

  Returns true if this set contains no elements.

  Returns true if this set contains no elements.
Returns: true if this set contains no elements

  Returns an iterator over the elements contained in this set in the order in which these elements were added.

  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.
Returns: an iterator over the elements in this set

  Removes the specified element from this set if it is present.

  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.)
Returns: true if this set contained the specified element
Parameters:
- o - object to be removed from this set, if present

  Removes from this set all of its elements that are contained in the specified collection.

  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.
Returns: true if this set changed as a result of the call
Parameters:
- c - collection containing elements to be removed from this set
Throws:
- 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
See Also: CopyOnWriteArraySet.remove(Object),

  Retains only the elements in this set that are contained in the specified collection.

  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.
Returns: true if this set changed as a result of the call
Parameters:
- c - collection containing elements to be retained in this set
Throws:
- 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
See Also: CopyOnWriteArraySet.remove(Object),

  Returns the number of elements in this set.

  Returns the number of elements in this set.
Returns: the number of elements in this set

  Returns an array containing all of the elements in this set.

  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.
Returns: an array containing all the elements in this set

  Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.

  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 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]);

Note that toArray(new Object[0]) is identical in function to toArray().
Returns: an array containing all the elements in this set
Parameters:
- 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.
Throws:
- 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