# ConcurrentSkipListSet

public class **ConcurrentSkipListSet** extends [AbstractSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractSet.html)\<E\>  
implements [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> [Cloneable](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Cloneable.html) [Serializable](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/Serializable.html) A scalable concurrent `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html` implementation based on
a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListMap.html`. The elements of the set are kept
sorted according to their {@linkplain Comparable natural ordering},
or by a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Comparator.html` provided at set creation time, depending
on which constructor is used.

This implementation provides expected average *log(n)* time
cost for the `contains`, `add`, and `remove`
operations and their variants. Insertion, removal, and access
operations safely execute concurrently by multiple threads.

Iterators and spliterators are
[*weakly consistent*](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/package-summary#Weakly).

Ascending ordered views and their iterators are faster than
descending ones.

Beware that, unlike in most collections, the `size`
method is *not* a constant-time operation. Because of the
asynchronous nature of these sets, determining the current number
of elements requires a traversal of the elements, and so may report
inaccurate results if this collection is modified during traversal.
Additionally, the bulk operations `addAll`,
`removeAll`, `retainAll`, `containsAll`,
`equals`, and `toArray` are *not* guaranteed
to be performed atomically. For example, an iterator operating
concurrently with an `addAll` operation might view only some
of the added elements.

This class and its iterators implement all of the
*optional* methods of the `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` and `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html`
interfaces. Like most other concurrent collection implementations,
this class does not permit the use of `null` elements,
because `null` arguments and return values cannot be reliably
distinguished from the absence of elements.

### Public Constructor Summary

|---|---|
|   | [ConcurrentSkipListSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#ConcurrentSkipListSet())() Constructs a new, empty set that orders its elements according to their {@linkplain Comparable natural ordering}. |
|   | [ConcurrentSkipListSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#ConcurrentSkipListSet(java.util.Comparator<?%20super%20E>))([Comparator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Comparator.html)\<? super E\> comparator) Constructs a new, empty set that orders its elements according to the specified comparator. |
|   | [ConcurrentSkipListSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#ConcurrentSkipListSet(java.util.Collection<?%20extends%20E>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<? extends E\> c) Constructs a new set containing the elements in the specified collection, that orders its elements according to their {@linkplain Comparable natural ordering}. |
|   | [ConcurrentSkipListSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#ConcurrentSkipListSet(java.util.SortedSet<E>))([SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> s) Constructs a new set containing the same elements and using the same ordering as the specified sorted set. |

### Public Method Summary

|---|---|
| boolean | [add](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#add(E))(E e) Adds the specified element to this set if it is not already present. |
| E | [ceiling](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#ceiling(E))(E e) Returns the least element in this set greater than or equal to the given element, or `null` if there is no such element. |
| void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#clear())() Removes all of the elements from this set. |
| [ConcurrentSkipListSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html)\<E\> | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#clone())() Returns a shallow copy of this `ConcurrentSkipListSet` instance. |
| [Comparator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Comparator.html)\<? super E\> | [comparator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#comparator())() Returns the comparator used to order the elements in this set, or null if this set uses the {@linkplain Comparable natural ordering} of its elements. |
| boolean | [contains](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#contains(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Returns `true` if this set contains the specified element. |
| [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [descendingIterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#descendingIterator())() Returns an iterator over the elements in this set in descending order. |
| [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [descendingSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#descendingSet())() Returns a reverse order view of the elements contained in this set. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this set for equality. |
| E | [first](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#first())() Returns the first (lowest) element currently in this set. |
| E | [floor](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#floor(E))(E e) Returns the greatest element in this set less than or equal to the given element, or `null` if there is no such element. |
| [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [headSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#headSet(E,%20boolean))(E toElement, boolean inclusive) Returns a view of the portion of this set whose elements are less than (or equal to, if `inclusive` is true) `toElement`. |
| [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [headSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#headSet(E))(E toElement) Returns a view of the portion of this set whose elements are strictly less than toElement. Equivalent to `headSet(toElement, false)`. |
| E | [higher](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#higher(E))(E e) Returns the least element in this set strictly greater than the given element, or `null` if there is no such element. |
| boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#isEmpty())() Returns `true` if this set contains no elements. |
| [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#iterator())() Returns an iterator over the elements in this set in ascending order. |
| E | [last](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#last())() Returns the last (highest) element currently in this set. |
| E | [lower](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#lower(E))(E e) Returns the greatest element in this set strictly less than the given element, or `null` if there is no such element. |
| E | [pollFirst](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#pollFirst())() Retrieves and removes the first (lowest) element, or returns `null` if this set is empty. |
| E | [pollLast](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#pollLast())() Retrieves and removes the last (highest) element, or returns `null` if this set is empty. |
| boolean | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Removes the specified element from this set if it is present. |
| boolean | [removeAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#removeAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Removes from this set all of its elements that are contained in the specified collection. |
| int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#size())() Returns the number of elements in this set. |
| [Spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html)\<E\> | [spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#spliterator())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html` over the elements in this set. |
| [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [subSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#subSet(E,%20boolean,%20E,%20boolean))(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) Returns a view of the portion of this set whose elements range from `fromElement` to `toElement`. |
| [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [subSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#subSet(E,%20E))(E fromElement, E toElement) Returns a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive. Equivalent to `subSet(fromElement, true, toElement, false)`. |
| [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [tailSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#tailSet(E,%20boolean))(E fromElement, boolean inclusive) Returns a view of the portion of this set whose elements are greater than (or equal to, if `inclusive` is true) `fromElement`. |
| [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [tailSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#tailSet(E))(E fromElement) Returns a view of the portion of this set whose elements are greater than or equal to fromElement. Equivalent to `tailSet(fromElement, true)`. |

### Inherited Method Summary

From class [java.util.AbstractSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractSet.html)

|---|---|
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractSet.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this set for equality. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractSet.html#hashCode())() Returns the hash code value for this set. |
| boolean | [removeAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractSet.html#removeAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Removes from this set all of its elements that are contained in the specified collection (optional operation). |

From class [java.util.AbstractCollection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html)

|---|---|
| boolean | [add](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#add(E))(E e) Ensures that this collection contains the specified element (optional operation). This implementation always throws an UnsupportedOperationException. |
| boolean | [addAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#addAll(java.util.Collection<?%20extends%20E>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<? extends E\> c) Adds all of the elements in the specified collection to this collection (optional operation). This implementation iterates over the specified collection, and adds each object returned by the iterator to this collection, in turn. |
| void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#clear())() Removes all of the elements from this collection (optional operation). This implementation iterates over this collection, removing each element using the Iterator.remove operation. |
| boolean | [contains](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#contains(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Returns true if this collection contains the specified element. This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element. |
| boolean | [containsAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#containsAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Returns true if this collection contains all of the elements in the specified collection. This implementation iterates over the specified collection, checking each element returned by the iterator in turn to see if it's contained in this collection. |
| boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#isEmpty())() Returns true if this collection contains no elements. This implementation returns size() == 0. |
| abstract [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#iterator())() Returns an iterator over the elements contained in this collection. |
| boolean | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Removes a single instance of the specified element from this collection, if it is present (optional operation). This implementation iterates over the collection looking for the specified element. |
| boolean | [removeAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#removeAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection. |
| boolean | [retainAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#retainAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Retains only the elements in this collection that are contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection. |
| abstract int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#size())() Returns the number of elements in this collection. |
| \<T\> T\[\] | [toArray](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#toArray(T[]))(T\[\] contents) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. This implementation returns an array containing all the elements returned by this collection's iterator in the same order, stored in consecutive elements of the array, starting with index `0`. |
| [Object\[\]](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [toArray](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#toArray())() Returns an array containing all of the elements in this collection. This implementation returns an array containing all the elements returned by this collection's iterator, in the same order, stored in consecutive elements of the array, starting with index `0`. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractCollection.html#toString())() Returns a string representation of this collection. |

From class [java.lang.Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#clone())() Creates and returns a copy of this `Object`. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| void | [finalize](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#finalize())() Invoked when the garbage collector has detected that this instance is no longer reachable. |
| final [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#getClass())() Returns the unique instance of `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html` that represents this object's class. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode())() Returns an integer hash code for this object. |
| final void | [notify](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notify())() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| final void | [notifyAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notifyAll())() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long,%20int))(long timeout, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long))(long timeout) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait())() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object. |

From interface [java.util.Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)

|---|---|
| abstract boolean | [add](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#add(E))(E e) Adds the specified element to this set if it is not already present (optional operation). |
| abstract boolean | [addAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#addAll(java.util.Collection<?%20extends%20E>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<? extends E\> c) Adds all of the elements in the specified collection to this set if they're not already present (optional operation). |
| abstract void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#clear())() Removes all of the elements from this set (optional operation). |
| abstract boolean | [contains](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#contains(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Returns `true` if this set contains the specified element. |
| abstract boolean | [containsAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#containsAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Returns `true` if this set contains all of the elements of the specified collection. |
| abstract boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this set for equality. |
| abstract int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#hashCode())() Returns the hash code value for this set. |
| abstract boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#isEmpty())() Returns `true` if this set contains no elements. |
| abstract [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#iterator())() Returns an iterator over the elements in this set. |
| abstract boolean | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Removes the specified element from this set if it is present (optional operation). |
| abstract boolean | [removeAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#removeAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Removes from this set all of its elements that are contained in the specified collection (optional operation). |
| abstract boolean | [retainAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#retainAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Retains only the elements in this set that are contained in the specified collection (optional operation). |
| abstract int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#size())() Returns the number of elements in this set (its cardinality). |
| [Spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html)\<E\> | [spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#spliterator())() Creates a `Spliterator` over the elements in this set. |
| abstract \<T\> T\[\] | [toArray](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#toArray(T[]))(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. |
| abstract [Object\[\]](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [toArray](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html#toArray())() Returns an array containing all of the elements in this set. |

From interface [java.util.Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)

|---|---|
| abstract boolean | [add](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#add(E))(E e) Ensures that this collection contains the specified element (optional operation). |
| abstract boolean | [addAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#addAll(java.util.Collection<?%20extends%20E>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<? extends E\> c) Adds all of the elements in the specified collection to this collection (optional operation). |
| abstract void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#clear())() Removes all of the elements from this collection (optional operation). |
| abstract boolean | [contains](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#contains(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Returns true if this collection contains the specified element. |
| abstract boolean | [containsAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#containsAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Returns true if this collection contains all of the elements in the specified collection. |
| abstract boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this collection for equality. |
| abstract int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#hashCode())() Returns the hash code value for this collection. |
| abstract boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#isEmpty())() Returns true if this collection contains no elements. |
| abstract [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#iterator())() Returns an iterator over the elements in this collection. |
| [Stream](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/stream/Stream.html)\<E\> | [parallelStream](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#parallelStream())() Returns a possibly parallel `Stream` with this collection as its source. |
| abstract boolean | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Removes a single instance of the specified element from this collection, if it is present (optional operation). |
| abstract boolean | [removeAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#removeAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
| boolean | [removeIf](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#removeIf(java.util.function.Predicate<?%20super%20E>))([Predicate](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/Predicate.html)\<? super E\> filter) Removes all of the elements of this collection that satisfy the given predicate. |
| abstract boolean | [retainAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#retainAll(java.util.Collection<?>))([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> c) Retains only the elements in this collection that are contained in the specified collection (optional operation). |
| abstract int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#size())() Returns the number of elements in this collection. |
| [Spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html)\<E\> | [spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#spliterator())() Creates a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html` over the elements in this collection. |
| [Stream](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/stream/Stream.html)\<E\> | [stream](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#stream())() Returns a sequential `Stream` with this collection as its source. |
| abstract \<T\> T\[\] | [toArray](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#toArray(T[]))(T\[\] a) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. |
| abstract [Object\[\]](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [toArray](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#toArray())() Returns an array containing all of the elements in this collection. |

From interface [java.util.NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)

|---|---|
| abstract E | [ceiling](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#ceiling(E))(E e) Returns the least element in this set greater than or equal to the given element, or `null` if there is no such element. |
| abstract [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [descendingIterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#descendingIterator())() Returns an iterator over the elements in this set, in descending order. |
| abstract [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [descendingSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#descendingSet())() Returns a reverse order view of the elements contained in this set. |
| abstract E | [floor](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#floor(E))(E e) Returns the greatest element in this set less than or equal to the given element, or `null` if there is no such element. |
| abstract [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [headSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#headSet(E,%20boolean))(E toElement, boolean inclusive) Returns a view of the portion of this set whose elements are less than (or equal to, if `inclusive` is true) `toElement`. |
| abstract [SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> | [headSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#headSet(E))(E toElement) Returns a view of the portion of this set whose elements are strictly less than toElement. Equivalent to `headSet(toElement, false)`. |
| abstract E | [higher](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#higher(E))(E e) Returns the least element in this set strictly greater than the given element, or `null` if there is no such element. |
| abstract [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#iterator())() Returns an iterator over the elements in this set, in ascending order. |
| abstract E | [lower](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#lower(E))(E e) Returns the greatest element in this set strictly less than the given element, or `null` if there is no such element. |
| abstract E | [pollFirst](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#pollFirst())() Retrieves and removes the first (lowest) element, or returns `null` if this set is empty. |
| abstract E | [pollLast](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#pollLast())() Retrieves and removes the last (highest) element, or returns `null` if this set is empty. |
| abstract [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [subSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#subSet(E,%20boolean,%20E,%20boolean))(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) Returns a view of the portion of this set whose elements range from `fromElement` to `toElement`. |
| abstract [SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> | [subSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#subSet(E,%20E))(E fromElement, E toElement) Returns a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive. Equivalent to `subSet(fromElement, true, toElement, false)`. |
| abstract [SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> | [tailSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#tailSet(E))(E fromElement) Returns a view of the portion of this set whose elements are greater than or equal to fromElement. Equivalent to `tailSet(fromElement, true)`. |
| abstract [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\> | [tailSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html#tailSet(E,%20boolean))(E fromElement, boolean inclusive) Returns a view of the portion of this set whose elements are greater than (or equal to, if `inclusive` is true) `fromElement`. |

From interface [java.lang.Iterable](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Iterable.html)

|---|---|
| void | [forEach](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Iterable.html#forEach(java.util.function.Consumer<?%20super%20T>))([Consumer](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/Consumer.html)\<? super T\> action) Performs the given action for each element of the `Iterable` until all elements have been processed or the action throws an exception. |
| abstract [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\> | [iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Iterable.html#iterator())() Returns an iterator over elements of type `T`. |
| [Spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html)\<E\> | [spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Iterable.html#spliterator())() Creates a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html` over the elements described by this `Iterable`. |

From interface [java.util.SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)

|---|---|
| abstract [Comparator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Comparator.html)\<? super E\> | [comparator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html#comparator())() Returns the comparator used to order the elements in this set, or null if this set uses the {@linkplain Comparable natural ordering} of its elements. |
| abstract E | [first](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html#first())() Returns the first (lowest) element currently in this set. |
| abstract [SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> | [headSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html#headSet(E))(E toElement) Returns a view of the portion of this set whose elements are strictly less than toElement. |
| abstract E | [last](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html#last())() Returns the last (highest) element currently in this set. |
| [Spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html)\<E\> | [spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html#spliterator())() Creates a `Spliterator` over the elements in this sorted set. |
| abstract [SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> | [subSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html#subSet(E,%20E))(E fromElement, E toElement) Returns a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive. |
| abstract [SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> | [tailSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html#tailSet(E))(E fromElement) Returns a view of the portion of this set whose elements are greater than or equal to fromElement. |

## Public Constructors

#### public
**ConcurrentSkipListSet**
()

Constructs a new, empty set that orders its elements according to
their {@linkplain Comparable natural ordering}.

#### public
**ConcurrentSkipListSet**
([Comparator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Comparator.html)\<? super E\> comparator)

Constructs a new, empty set that orders its elements according to
the specified comparator.

##### Parameters

| comparator | the comparator that will be used to order this set. If `null`, the {@linkplain Comparable natural ordering} of the elements will be used. |
|---|---|

#### public
**ConcurrentSkipListSet**
([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<? extends E\> c)

Constructs a new set containing the elements in the specified
collection, that orders its elements according to their
{@linkplain Comparable natural ordering}.

##### Parameters

| c | The elements that will comprise the new set |
|---|---|

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) | if the elements in `c` are not `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Comparable.html`, or are not mutually comparable |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified collection or any of its elements are null |
|---|---|

#### public
**ConcurrentSkipListSet**
([SortedSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/SortedSet.html)\<E\> s)

Constructs a new set containing the same elements and using the
same ordering as the specified sorted set.

##### Parameters

| s | sorted set whose elements will comprise the new set |
|---|---|

##### Throws

| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified sorted set or any of its elements are null |
|---|---|

## Public Methods

#### 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.equals(e2)`.
If this set already contains the element, the call leaves the set
unchanged and returns `false`.

##### Parameters

| e | element to be added to this set |
|---|---|

##### Returns

- `true` if this set did not already contain the specified element

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) | if `e` cannot be compared with the elements currently in this set |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified element is null |
|---|---|

#### public E
**ceiling**
(E e)

Returns the least element in this set greater than or equal to
the given element, or `null` if there is no such element.

##### Parameters

| e | the value to match |
|---|---|

##### Returns

- the least element greater than or equal to `e`, or `null` if there is no such element

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified element is null |
|---|---|

#### public void
**clear**
()

Removes all of the elements from this set.

#### public [ConcurrentSkipListSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html)\<E\>
**clone**
()

Returns a shallow copy of this `ConcurrentSkipListSet`
instance. (The elements themselves are not cloned.)

##### Returns

- a shallow copy of this set

#### public [Comparator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Comparator.html)\<? super E\>
**comparator**
()

Returns the comparator used to order the elements in this set,
or null if this set uses the {@linkplain Comparable
natural ordering} of its elements.

##### Returns

- the comparator used to order the elements in this set, or null if this set uses the natural ordering of its elements

#### public boolean
**contains**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) 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.equals(e)`.

##### Parameters

| o | object to be checked for containment in this set |
|---|---|

##### Returns

- `true` if this set contains the specified element

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) | if the specified element cannot be compared with the elements currently in this set |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified element is null |
|---|---|

#### public [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\>
**descendingIterator**
()

Returns an iterator over the elements in this set in descending order.

##### Returns

- an iterator over the elements in this set in descending order

#### public [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\>
**descendingSet**
()

Returns a reverse order view of the elements contained in this set.
The descending set is backed by this set, so changes to the set are
reflected in the descending set, and vice-versa.

The returned set has an ordering equivalent to
`https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collections.html#reverseOrder(java.util.Comparator<T>)``(comparator())`.
The expression `s.descendingSet().descendingSet()` returns a
view of `s` essentially equivalent to `s`.

##### Returns

- a reverse order view of this set

#### public boolean
**equals**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o)

Compares the specified object with this set for equality. Returns
`true` if the specified object is also a set, the two sets
have the same size, and every member of the specified set is
contained in this set (or equivalently, every member of this set is
contained in the specified set). This definition ensures that the
equals method works properly across different implementations of the
set interface.

##### Parameters

| o | the object to be compared for equality with this set |
|---|---|

##### Returns

- `true` if the specified object is equal to this set

#### public E
**first**
()

Returns the first (lowest) element currently in this set.

##### Returns

- the first (lowest) element currently in this set

##### Throws

| [NoSuchElementException](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NoSuchElementException.html) |   |
|---|---|

#### public E
**floor**
(E e)

Returns the greatest element in this set less than or equal to
the given element, or `null` if there is no such element.

##### Parameters

| e | the value to match |
|---|---|

##### Returns

- the greatest element less than or equal to `e`, or `null` if there is no such element

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified element is null |
|---|---|

#### public [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\>
**headSet**
(E toElement, boolean inclusive)

Returns a view of the portion of this set whose elements are less than
(or equal to, if `inclusive` is true) `toElement`. The
returned set is backed by this set, so changes in the returned set are
reflected in this set, and vice-versa. The returned set supports all
optional set operations that this set supports.

The returned set will throw an `IllegalArgumentException`
on an attempt to insert an element outside its range.

##### Parameters

| toElement | high endpoint of the returned set |
| inclusive | `true` if the high endpoint is to be included in the returned view |
|---|---|

##### Returns

- a view of the portion of this set whose elements are less than (or equal to, if `inclusive` is true) `toElement`

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if `toElement` is null |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) |   |
|---|---|

#### public [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\>
**headSet**
(E toElement)

Returns a view of the portion of this set whose elements are
strictly less than toElement. The returned set is
backed by this set, so changes in the returned set are
reflected in this set, and vice-versa. The returned set
supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException
on an attempt to insert an element outside its range.

Equivalent to `headSet(toElement, false)`.

##### Parameters

| toElement | high endpoint (exclusive) of the returned set |
|---|---|

##### Returns

- a view of the portion of this set whose elements are strictly less than toElement

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if `toElement` is null |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) |   |
|---|---|

#### public E
**higher**
(E e)

Returns the least element in this set strictly greater than the
given element, or `null` if there is no such element.

##### Parameters

| e | the value to match |
|---|---|

##### Returns

- the least element greater than `e`, or `null` if there is no such element

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified element is null |
|---|---|

#### public boolean
**isEmpty**
()

Returns `true` if this set contains no elements.

##### Returns

- `true` if this set contains no elements

#### public [Iterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Iterator.html)\<E\>
**iterator**
()

Returns an iterator over the elements in this set in ascending order.

##### Returns

- an iterator over the elements in this set in ascending order

#### public E
**last**
()

Returns the last (highest) element currently in this set.

##### Returns

- the last (highest) element currently in this set

##### Throws

| [NoSuchElementException](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NoSuchElementException.html) |   |
|---|---|

#### public E
**lower**
(E e)

Returns the greatest element in this set strictly less than the
given element, or `null` if there is no such element.

##### Parameters

| e | the value to match |
|---|---|

##### Returns

- the greatest element less than `e`, or `null` if there is no such element

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified element is null |
|---|---|

#### public E
**pollFirst**
()

Retrieves and removes the first (lowest) element,
or returns `null` if this set is empty.

##### Returns

- the first element, or `null` if this set is empty

#### public E
**pollLast**
()

Retrieves and removes the last (highest) element,
or returns `null` if this set is empty.

##### Returns

- the last element, or `null` if this set is empty

#### public boolean
**remove**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o)

Removes the specified element from this set if it is present.
More formally, removes an element `e` such that
`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.)

##### Parameters

| o | object to be removed from this set, if present |
|---|---|

##### Returns

- `true` if this set contained the specified element

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) | if `o` cannot be compared with the elements currently in this set |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified element is null |
|---|---|

#### public boolean
**removeAll**
([Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<?\> 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.

##### Parameters

| c | collection containing elements to be removed from this set |
|---|---|

##### Returns

- `true` if this set changed as a result of the call

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) | if the class of an element of this set is incompatible with the specified collection ([optional](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html#optional-restrictions)) |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified collection or any of its elements are null |
|---|---|

#### public int
**size**
()

Returns the number of elements in this set. If this set
contains more than `Integer.MAX_VALUE` elements, it
returns `Integer.MAX_VALUE`.

Beware that, unlike in most collections, this method is
*NOT* a constant-time operation. Because of the
asynchronous nature of these sets, determining the current
number of elements requires traversing them all to count them.
Additionally, it is possible for the size to change during
execution of this method, in which case the returned result
will be inaccurate. Thus, this method is typically not very
useful in concurrent applications.

##### Returns

- the number of elements in this set

#### public [Spliterator](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html)\<E\>
**spliterator**
()

Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html` over the elements in this set.

The `Spliterator` reports `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html#CONCURRENT`,
`https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html#NONNULL`, `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html#DISTINCT`,
`https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html#SORTED` and `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html#ORDERED`, with an
encounter order that is ascending order. Overriding implementations
should document the reporting of additional characteristic values.

The spliterator's comparator (see
`https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Spliterator.html#getComparator()`) is `null` if
the set's comparator (see `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/ConcurrentSkipListSet.html#comparator()`) is `null`.
Otherwise, the spliterator's comparator is the same as or imposes the
same total ordering as the set's comparator.

##### Returns

- a `Spliterator` over the elements in this set

#### public [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\>
**subSet**
(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)

Returns a view of the portion of this set whose elements range from
`fromElement` to `toElement`. If `fromElement` and
`toElement` are equal, the returned set is empty unless `fromInclusive` and `toInclusive` are both true. The returned set
is backed by this set, so changes in the returned set are reflected in
this set, and vice-versa. The returned set supports all optional set
operations that this set supports.

The returned set will throw an `IllegalArgumentException`
on an attempt to insert an element outside its range.

##### Parameters

| fromElement | low endpoint of the returned set |
| fromInclusive | `true` if the low endpoint is to be included in the returned view |
| toElement | high endpoint of the returned set |
| toInclusive | `true` if the high endpoint is to be included in the returned view |
|---|---|

##### Returns

- a view of the portion of this set whose elements range from `fromElement`, inclusive, to `toElement`, exclusive

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if `fromElement` or `toElement` is null |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) |   |
|---|---|

#### public [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\>
**subSet**
(E fromElement, E toElement)

Returns a view of the portion of this set whose elements range
from fromElement, inclusive, to toElement,
exclusive. (If fromElement and toElement are
equal, the returned set is empty.) The returned set is backed
by this set, so changes in the returned set are reflected in
this set, and vice-versa. The returned set supports all
optional set operations that this set supports.

The returned set will throw an IllegalArgumentException
on an attempt to insert an element outside its range.

Equivalent to `subSet(fromElement, true, toElement, false)`.

##### Parameters

| fromElement | low endpoint (inclusive) of the returned set |
| toElement | high endpoint (exclusive) of the returned set |
|---|---|

##### Returns

- a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if `fromElement` or `toElement` is null |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) |   |
|---|---|

#### public [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\>
**tailSet**
(E fromElement, boolean inclusive)

Returns a view of the portion of this set whose elements are greater
than (or equal to, if `inclusive` is true) `fromElement`.
The returned set is backed by this set, so changes in the returned set
are reflected in this set, and vice-versa. The returned set supports
all optional set operations that this set supports.

The returned set will throw an `IllegalArgumentException`
on an attempt to insert an element outside its range.

##### Parameters

| fromElement | low endpoint of the returned set |
| inclusive | `true` if the low endpoint is to be included in the returned view |
|---|---|

##### Returns

- a view of the portion of this set whose elements are greater than or equal to `fromElement`

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if `fromElement` is null |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) |   |
|---|---|

#### public [NavigableSet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/NavigableSet.html)\<E\>
**tailSet**
(E fromElement)

Returns a view of the portion of this set whose elements are
greater than or equal to fromElement. The returned
set is backed by this set, so changes in the returned set are
reflected in this set, and vice-versa. The returned set
supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException
on an attempt to insert an element outside its range.

Equivalent to `tailSet(fromElement, true)`.

##### Parameters

| fromElement | low endpoint (inclusive) of the returned set |
|---|---|

##### Returns

- a view of the portion of this set whose elements are greater than or equal to fromElement

##### Throws

| [ClassCastException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassCastException.html) |   |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if `fromElement` is null |
| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) |   |
|---|---|