Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary: [Ctors](https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#pubctors) \| [Methods](https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#pubmethods) \| [Inherited Methods](https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#inhmethods)

# ConcurrentSkipListSet


`
public


class
ConcurrentSkipListSet
`


`


`

`


`

`

extends https://developer.android.com/reference/java/util/AbstractSet<E>


`

`


implements

https://developer.android.com/reference/java/lang/Cloneable,

https://developer.android.com/reference/java/util/NavigableSet<E>,

https://developer.android.com/reference/java/io/Serializable


`

|---|---|---|---|
| [java.lang.Object](https://developer.android.com/reference/java/lang/Object) ||||
| ↳ | [java.util.AbstractCollection](https://developer.android.com/reference/java/util/AbstractCollection)\<E\> |||
|   | ↳ | [java.util.AbstractSet](https://developer.android.com/reference/java/util/AbstractSet)\<E\> ||
|   |   | ↳ | java.util.concurrent.ConcurrentSkipListSet\<E\> |

<br />

*** ** * ** ***

A scalable concurrent `https://developer.android.com/reference/java/util/NavigableSet` implementation based on
a `https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListMap`. The elements of the set are kept
sorted according to their [natural ordering](https://developer.android.com/reference/java/lang/Comparable),
or by a `https://developer.android.com/reference/java/util/Comparator` 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://developer.android.com/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.

Bulk operations that add, remove, or examine multiple elements,
such as `https://developer.android.com/reference/java/util/AbstractCollection#addAll(java.util.Collection<?%20extends%20E>)`, `https://developer.android.com/reference/java/util/Collection#removeIf(java.util.function.Predicate<?%20super%20E>)` or `https://developer.android.com/reference/java/lang/Iterable#forEach(java.util.function.Consumer<?%20super%20T>)`,
are *not* guaranteed to be performed atomically.
For example, a `forEach` traversal concurrent with an `addAll` operation might observe only some of the added elements.

This class and its iterators implement all of the
*optional* methods of the `https://developer.android.com/reference/java/util/Set` and `https://developer.android.com/reference/java/util/Iterator`
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.

This class is a member of the
[Java Collections Framework](https://reference/java/util/package-summary.html#CollectionsFramework).

## Summary

| ### Public constructors ||
|---|---|
| ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#ConcurrentSkipListSet()() ` Constructs a new, empty set that orders its elements according to their [natural ordering](https://developer.android.com/reference/java/lang/Comparable). |
| ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#ConcurrentSkipListSet(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? extends E> c) ` Constructs a new set containing the elements in the specified collection, that orders its elements according to their [natural ordering](https://developer.android.com/reference/java/lang/Comparable). |
| ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#ConcurrentSkipListSet(java.util.Comparator<?%20super%20E>)(https://developer.android.com/reference/java/util/Comparator<? super E> comparator) ` Constructs a new, empty set that orders its elements according to the specified comparator. |
| ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#ConcurrentSkipListSet(java.util.SortedSet<E>)(https://developer.android.com/reference/java/util/SortedSet<E> s) ` Constructs a new set containing the same elements and using the same ordering as the specified sorted set. |

| ### Public methods ||
|---|---|
| ` boolean` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#add(E)(E e) ` Adds the specified element to this set if it is not already present. |
| ` void` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#addFirst(E)(E e) ` Throws `UnsupportedOperationException`. |
| ` void` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#addLast(E)(E e) ` Throws `UnsupportedOperationException`. |
| ` E` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#clear()() ` Removes all of the elements from this set. |
| ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#clone()() ` Returns a shallow copy of this `ConcurrentSkipListSet` instance. |
| ` https://developer.android.com/reference/java/util/Comparator<? super E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#comparator()() ` Returns the comparator used to order the elements in this set, or `null` if this set uses the [natural ordering](https://developer.android.com/reference/java/lang/Comparable) of its elements. |
| ` boolean` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#contains(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Returns `true` if this set contains the specified element. |
| ` https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#descendingIterator()() ` Returns an iterator over the elements in this set in descending order. |
| ` https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#descendingSet()() ` Returns a reverse order view of the elements contained in this set. |
| ` boolean` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Compares the specified object with this set for equality. |
| ` E` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#first()() ` Returns the first (lowest) element currently in this set. |
| ` E` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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. |
| ` https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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`. |
| ` https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#isEmpty()() ` Returns `true` if this set contains no elements. |
| ` https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#iterator()() ` Returns an iterator over the elements in this set in ascending order. |
| ` E` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#last()() ` Returns the last (highest) element currently in this set. |
| ` E` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#pollFirst()() ` Retrieves and removes the first (lowest) element, or returns `null` if this set is empty (optional operation). |
| ` E` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#pollLast()() ` Retrieves and removes the last (highest) element, or returns `null` if this set is empty (optional operation). |
| ` boolean` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#remove(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Removes the specified element from this set if it is present. |
| ` boolean` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#removeAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Removes from this set all of its elements that are contained in the specified collection. |
| ` int` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#size()() ` Returns the number of elements in this set. |
| ` https://developer.android.com/reference/java/util/Spliterator<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#spliterator()() ` Returns a `https://developer.android.com/reference/java/util/Spliterator` over the elements in this set. |
| ` https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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`. |
| ` https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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)`. |
| ` https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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`. |
| ` https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#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 methods |
|---|---|
| From class ` https://developer.android.com/reference/java/util/AbstractSet ` |---|---| | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractSet#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Compares the specified object with this set for equality. | | ` int` | ` https://developer.android.com/reference/java/util/AbstractSet#hashCode()() ` Returns the hash code value for this set. | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractSet#removeAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Removes from this set all of its elements that are contained in the specified collection (optional operation). | ||
| From class ` https://developer.android.com/reference/java/util/AbstractCollection ` |---|---| | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#add(E)(E e) ` Ensures that this collection contains the specified element (optional operation). | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#addAll(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? extends E> c) ` Adds all of the elements in the specified collection to this collection (optional operation). | | ` void` | ` https://developer.android.com/reference/java/util/AbstractCollection#clear()() ` Removes all of the elements from this collection (optional operation). | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#contains(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Returns `true` if this collection contains the specified element. | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#containsAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Returns `true` if this collection contains all of the elements in the specified collection. | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#isEmpty()() ` Returns `true` if this collection contains no elements. | | ` abstract https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/util/AbstractCollection#iterator()() ` Returns an iterator over the elements contained in this collection. | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#remove(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Removes a single instance of the specified element from this collection, if it is present (optional operation). | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#removeAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Removes all of this collection's elements that are also contained in the specified collection (optional operation). | | ` boolean` | ` https://developer.android.com/reference/java/util/AbstractCollection#retainAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Retains only the elements in this collection that are contained in the specified collection (optional operation). | | ` abstract int` | ` https://developer.android.com/reference/java/util/AbstractCollection#size()() ` Returns the number of elements in this collection. | | ` <T> T[]` | ` https://developer.android.com/reference/java/util/AbstractCollection#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. | | ` https://developer.android.com/reference/java/lang/Object` | ` https://developer.android.com/reference/java/util/AbstractCollection#toArray()() ` Returns an array containing all of the elements in this collection. | | ` https://developer.android.com/reference/java/lang/String` | ` https://developer.android.com/reference/java/util/AbstractCollection#toString()() ` Returns a string representation of this collection. | ||
| From class ` https://developer.android.com/reference/java/lang/Object ` |---|---| | ` https://developer.android.com/reference/java/lang/Object` | ` https://developer.android.com/reference/java/lang/Object#clone()() ` Creates and returns a copy of this object. | | ` boolean` | ` https://developer.android.com/reference/java/lang/Object#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object obj) ` Indicates whether some other object is "equal to" this one. | | ` void` | ` https://developer.android.com/reference/java/lang/Object#finalize()() ` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. | | ` final https://developer.android.com/reference/java/lang/Class<?>` | ` https://developer.android.com/reference/java/lang/Object#getClass()() ` Returns the runtime class of this `Object`. | | ` int` | ` https://developer.android.com/reference/java/lang/Object#hashCode()() ` Returns a hash code value for the object. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#notify()() ` Wakes up a single thread that is waiting on this object's monitor. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#notifyAll()() ` Wakes up all threads that are waiting on this object's monitor. | | ` https://developer.android.com/reference/java/lang/String` | ` https://developer.android.com/reference/java/lang/Object#toString()() ` Returns a string representation of the object. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#wait(long,%20int)(long timeoutMillis, int nanos) ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#wait(long)(long timeoutMillis) ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#wait()() ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*. | ||
| From interface ` https://developer.android.com/reference/java/util/Set ` |---|---| | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#add(E)(E e) ` Adds the specified element to this set if it is not already present (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#addAll(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? 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` | ` https://developer.android.com/reference/java/util/Set#clear()() ` Removes all of the elements from this set (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#contains(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Returns `true` if this set contains the specified element. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#containsAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Returns `true` if this set contains all of the elements of the specified collection. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#copyOf(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? extends E> coll) ` Returns an [unmodifiable Set](https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#unmodifiable) containing the elements of the given Collection. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Compares the specified object with this set for equality. | | ` abstract int` | ` https://developer.android.com/reference/java/util/Set#hashCode()() ` Returns the hash code value for this set. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#isEmpty()() ` Returns `true` if this set contains no elements. | | ` abstract https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/util/Set#iterator()() ` Returns an iterator over the elements in this set. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E)(E e1, E e2, E e3) ` Returns an unmodifiable set containing three elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E,%20E,%20E,%20E,%20E,%20E,%20E)(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) ` Returns an unmodifiable set containing nine elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E,%20E,%20E)(E e1, E e2, E e3, E e4, E e5) ` Returns an unmodifiable set containing five elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E,%20E,%20E,%20E)(E e1, E e2, E e3, E e4, E e5, E e6) ` Returns an unmodifiable set containing six elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E,%20E,%20E,%20E,%20E,%20E)(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) ` Returns an unmodifiable set containing eight elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E[])(E... elements) ` Returns an unmodifiable set containing an arbitrary number of elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of()() ` Returns an unmodifiable set containing zero elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E,%20E,%20E,%20E,%20E,%20E,%20E,%20E)(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) ` Returns an unmodifiable set containing ten elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E)(E e1, E e2) ` Returns an unmodifiable set containing two elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E,%20E,%20E,%20E,%20E)(E e1, E e2, E e3, E e4, E e5, E e6, E e7) ` Returns an unmodifiable set containing seven elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E,%20E,%20E,%20E)(E e1, E e2, E e3, E e4) ` Returns an unmodifiable set containing four elements. | | ` static <E> https://developer.android.com/reference/java/util/Set<E>` | ` https://developer.android.com/reference/java/util/Set#of(E)(E e1) ` Returns an unmodifiable set containing one element. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#remove(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Removes the specified element from this set if it is present (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#removeAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Removes from this set all of its elements that are contained in the specified collection (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Set#retainAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Retains only the elements in this set that are contained in the specified collection (optional operation). | | ` abstract int` | ` https://developer.android.com/reference/java/util/Set#size()() ` Returns the number of elements in this set (its cardinality). | | ` default https://developer.android.com/reference/java/util/Spliterator<E>` | ` https://developer.android.com/reference/java/util/Set#spliterator()() ` Creates a `Spliterator` over the elements in this set. | | ` abstract https://developer.android.com/reference/java/lang/Object` | ` https://developer.android.com/reference/java/util/Set#toArray()() ` Returns an array containing all of the elements in this set. | | ` abstract <T> T[]` | ` https://developer.android.com/reference/java/util/Set#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. | ||
| From interface ` https://developer.android.com/reference/java/util/Collection ` |---|---| | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#add(E)(E e) ` Ensures that this collection contains the specified element (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#addAll(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? extends E> c) ` Adds all of the elements in the specified collection to this collection (optional operation). | | ` abstract void` | ` https://developer.android.com/reference/java/util/Collection#clear()() ` Removes all of the elements from this collection (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#contains(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Returns `true` if this collection contains the specified element. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#containsAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Returns `true` if this collection contains all of the elements in the specified collection. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Compares the specified object with this collection for equality. | | ` abstract int` | ` https://developer.android.com/reference/java/util/Collection#hashCode()() ` Returns the hash code value for this collection. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#isEmpty()() ` Returns `true` if this collection contains no elements. | | ` abstract https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/util/Collection#iterator()() ` Returns an iterator over the elements in this collection. | | ` default https://developer.android.com/reference/java/util/stream/Stream<E>` | ` https://developer.android.com/reference/java/util/Collection#parallelStream()() ` Returns a possibly parallel `Stream` with this collection as its source. | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#remove(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) ` Removes a single instance of the specified element from this collection, if it is present (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#removeAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Removes all of this collection's elements that are also contained in the specified collection (optional operation). | | ` default boolean` | ` https://developer.android.com/reference/java/util/Collection#removeIf(java.util.function.Predicate<?%20super%20E>)(https://developer.android.com/reference/java/util/function/Predicate<? super E> filter) ` Removes all of the elements of this collection that satisfy the given predicate (optional operation). | | ` abstract boolean` | ` https://developer.android.com/reference/java/util/Collection#retainAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) ` Retains only the elements in this collection that are contained in the specified collection (optional operation). | | ` abstract int` | ` https://developer.android.com/reference/java/util/Collection#size()() ` Returns the number of elements in this collection. | | ` default https://developer.android.com/reference/java/util/Spliterator<E>` | ` https://developer.android.com/reference/java/util/Collection#spliterator()() ` Creates a `https://developer.android.com/reference/java/util/Spliterator` over the elements in this collection. | | ` default https://developer.android.com/reference/java/util/stream/Stream<E>` | ` https://developer.android.com/reference/java/util/Collection#stream()() ` Returns a sequential `Stream` with this collection as its source. | | ` abstract <T> T[]` | ` https://developer.android.com/reference/java/util/Collection#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 https://developer.android.com/reference/java/lang/Object` | ` https://developer.android.com/reference/java/util/Collection#toArray()() ` Returns an array containing all of the elements in this collection. | | ` default <T> T[]` | ` https://developer.android.com/reference/java/util/Collection#toArray(java.util.function.IntFunction<T[]>)(https://developer.android.com/reference/java/util/function/IntFunction<T[]> generator) ` Returns an array containing all of the elements in this collection, using the provided `generator` function to allocate the returned array. | ||
| From interface ` https://developer.android.com/reference/java/util/NavigableSet ` |---|---| | ` abstract E` | ` https://developer.android.com/reference/java/util/NavigableSet#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 https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#descendingIterator()() ` Returns an iterator over the elements in this set, in descending order. | | ` abstract https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#descendingSet()() ` Returns a reverse order view of the elements contained in this set. | | ` abstract E` | ` https://developer.android.com/reference/java/util/NavigableSet#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 https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#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 https://developer.android.com/reference/java/util/SortedSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#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` | ` https://developer.android.com/reference/java/util/NavigableSet#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 https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#iterator()() ` Returns an iterator over the elements in this set, in ascending order. | | ` abstract E` | ` https://developer.android.com/reference/java/util/NavigableSet#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` | ` https://developer.android.com/reference/java/util/NavigableSet#pollFirst()() ` Retrieves and removes the first (lowest) element, or returns `null` if this set is empty (optional operation). | | ` abstract E` | ` https://developer.android.com/reference/java/util/NavigableSet#pollLast()() ` Retrieves and removes the last (highest) element, or returns `null` if this set is empty (optional operation). | | ` default E` | ` https://developer.android.com/reference/java/util/NavigableSet#removeFirst()() ` Removes and returns the first element of this collection (optional operation). | | ` default E` | ` https://developer.android.com/reference/java/util/NavigableSet#removeLast()() ` Removes and returns the last element of this collection (optional operation). | | ` default https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#reversed()() ` Returns a reverse-ordered [view](https://developer.android.com/reference/java/util/concurrent/Collection#view) of this collection. This method is equivalent to `https://developer.android.com/reference/java/util/NavigableSet#descendingSet()`. | | ` abstract https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#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 https://developer.android.com/reference/java/util/SortedSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#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 https://developer.android.com/reference/java/util/SortedSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#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 https://developer.android.com/reference/java/util/NavigableSet<E>` | ` https://developer.android.com/reference/java/util/NavigableSet#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 ` https://developer.android.com/reference/java/lang/Iterable ` |---|---| | ` default void` | ` https://developer.android.com/reference/java/lang/Iterable#forEach(java.util.function.Consumer<?%20super%20T>)(https://developer.android.com/reference/java/util/function/Consumer<? 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 https://developer.android.com/reference/java/util/Iterator<E>` | ` https://developer.android.com/reference/java/lang/Iterable#iterator()() ` Returns an iterator over elements of type `T`. | | ` default https://developer.android.com/reference/java/util/Spliterator<E>` | ` https://developer.android.com/reference/java/lang/Iterable#spliterator()() ` Creates a `https://developer.android.com/reference/java/util/Spliterator` over the elements described by this `Iterable`. | ||
| From interface ` https://developer.android.com/reference/java/util/SortedSet ` |---|---| | ` default void` | ` https://developer.android.com/reference/java/util/SortedSet#addFirst(E)(E e) ` Throws `UnsupportedOperationException`. | | ` default void` | ` https://developer.android.com/reference/java/util/SortedSet#addLast(E)(E e) ` Throws `UnsupportedOperationException`. | | ` abstract https://developer.android.com/reference/java/util/Comparator<? super E>` | ` https://developer.android.com/reference/java/util/SortedSet#comparator()() ` Returns the comparator used to order the elements in this set, or `null` if this set uses the [natural ordering](https://developer.android.com/reference/java/lang/Comparable) of its elements. | | ` abstract E` | ` https://developer.android.com/reference/java/util/SortedSet#first()() ` Returns the first (lowest) element currently in this set. | | ` default E` | ` https://developer.android.com/reference/java/util/SortedSet#getFirst()() ` Gets the first element of this collection. | | ` default E` | ` https://developer.android.com/reference/java/util/SortedSet#getLast()() ` Gets the last element of this collection. | | ` abstract https://developer.android.com/reference/java/util/SortedSet<E>` | ` https://developer.android.com/reference/java/util/SortedSet#headSet(E)(E toElement) ` Returns a view of the portion of this set whose elements are strictly less than `toElement`. | | ` abstract E` | ` https://developer.android.com/reference/java/util/SortedSet#last()() ` Returns the last (highest) element currently in this set. | | ` default E` | ` https://developer.android.com/reference/java/util/SortedSet#removeFirst()() ` Removes and returns the first element of this collection (optional operation). | | ` default E` | ` https://developer.android.com/reference/java/util/SortedSet#removeLast()() ` Removes and returns the last element of this collection (optional operation). | | ` default https://developer.android.com/reference/java/util/SortedSet<E>` | ` https://developer.android.com/reference/java/util/SortedSet#reversed()() ` Returns a reverse-ordered [view](https://developer.android.com/reference/java/util/concurrent/Collection#view) of this collection. | | ` default https://developer.android.com/reference/java/util/Spliterator<E>` | ` https://developer.android.com/reference/java/util/SortedSet#spliterator()() ` Creates a `Spliterator` over the elements in this sorted set. | | ` abstract https://developer.android.com/reference/java/util/SortedSet<E>` | ` https://developer.android.com/reference/java/util/SortedSet#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 https://developer.android.com/reference/java/util/SortedSet<E>` | ` https://developer.android.com/reference/java/util/SortedSet#tailSet(E)(E fromElement) ` Returns a view of the portion of this set whose elements are greater than or equal to `fromElement`. | ||
| From interface ` https://developer.android.com/reference/java/util/SequencedSet ` |---|---| | ` abstract https://developer.android.com/reference/java/util/SequencedSet<E>` | ` https://developer.android.com/reference/java/util/SequencedSet#reversed()() ` Returns a reverse-ordered [view](https://developer.android.com/reference/java/util/concurrent/Collection#view) of this collection. | ||
| From interface ` https://developer.android.com/reference/java/util/SequencedCollection ` |---|---| | ` default void` | ` https://developer.android.com/reference/java/util/SequencedCollection#addFirst(E)(E e) ` Adds an element as the first element of this collection (optional operation). | | ` default void` | ` https://developer.android.com/reference/java/util/SequencedCollection#addLast(E)(E e) ` Adds an element as the last element of this collection (optional operation). | | ` default E` | ` https://developer.android.com/reference/java/util/SequencedCollection#getFirst()() ` Gets the first element of this collection. | | ` default E` | ` https://developer.android.com/reference/java/util/SequencedCollection#getLast()() ` Gets the last element of this collection. | | ` default E` | ` https://developer.android.com/reference/java/util/SequencedCollection#removeFirst()() ` Removes and returns the first element of this collection (optional operation). | | ` default E` | ` https://developer.android.com/reference/java/util/SequencedCollection#removeLast()() ` Removes and returns the last element of this collection (optional operation). | | ` abstract https://developer.android.com/reference/java/util/SequencedCollection<E>` | ` https://developer.android.com/reference/java/util/SequencedCollection#reversed()() ` Returns a reverse-ordered [view](https://developer.android.com/reference/java/util/concurrent/Collection#view) of this collection. | ||

## Public constructors

### ConcurrentSkipListSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public ConcurrentSkipListSet ()
```

Constructs a new, empty set that orders its elements according to
their [natural ordering](https://developer.android.com/reference/java/lang/Comparable).

<br />

### ConcurrentSkipListSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public ConcurrentSkipListSet (Collection<? extends E> c)
```

Constructs a new set containing the elements in the specified
collection, that orders its elements according to their
[natural ordering](https://developer.android.com/reference/java/lang/Comparable).

<br />

| Parameters ||
|---|---|
| `c` | `Collection`: The elements that will comprise the new set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` | if the elements in `c` are not `https://developer.android.com/reference/java/lang/Comparable`, or are not mutually comparable |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified collection or any of its elements are null |

### ConcurrentSkipListSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public ConcurrentSkipListSet (Comparator<? super E> comparator)
```

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

<br />

| Parameters ||
|---|---|
| `comparator` | `Comparator`: the comparator that will be used to order this set. If `null`, the [natural ordering](https://developer.android.com/reference/java/lang/Comparable) of the elements will be used. <br /> |

### ConcurrentSkipListSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public ConcurrentSkipListSet (SortedSet<E> s)
```

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

<br />

| Parameters ||
|---|---|
| `s` | `SortedSet`: sorted set whose elements will comprise the new set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified sorted set or any of its elements are null |

## Public methods

### add

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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`.

<br />

| Parameters ||
|---|---|
| `e` | `E`: element to be added to this set <br /> |

| Returns ||
|---|---|
| `boolean` | `true` if this set did not already contain the specified element <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` | if `e` cannot be compared with the elements currently in this set |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null |

### addFirst

Added in [API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public void addFirst (E e)
```

Throws `UnsupportedOperationException`. The encounter order induced by this
set's comparison method determines the position of elements, so explicit positioning
is not supported.

<br />

| Parameters ||
|---|---|
| `e` | `E`: the element to be added <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/UnsupportedOperationException` | always |

### addLast

Added in [API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public void addLast (E e)
```

Throws `UnsupportedOperationException`. The encounter order induced by this
set's comparison method determines the position of elements, so explicit positioning
is not supported.

<br />

| Parameters ||
|---|---|
| `e` | `E`: the element to be added. <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/UnsupportedOperationException` | always |

### ceiling

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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.

<br />

| Parameters ||
|---|---|
| `e` | `E`: the value to match <br /> |

| Returns ||
|---|---|
| `E` | the least element greater than or equal to `e`, or `null` if there is no such element <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null |

### clear

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public void clear ()
```

Removes all of the elements from this set.

<br />

### clone

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public ConcurrentSkipListSet<E> clone ()
```

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

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet<E>` | a shallow copy of this set <br /> |

### comparator

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<? super E> comparator ()
```

Returns the comparator used to order the elements in this set,
or `null` if this set uses the [natural ordering](https://developer.android.com/reference/java/lang/Comparable) of its elements.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<? super E>` | the comparator used to order the elements in this set, or `null` if this set uses the natural ordering of its elements <br /> |

### contains

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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.equals(e)`.

<br />

| Parameters ||
|---|---|
| `o` | `Object`: object to be checked for containment in this set <br /> |

| Returns ||
|---|---|
| `boolean` | `true` if this set contains the specified element <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` | if the specified element cannot be compared with the elements currently in this set |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null |

### descendingIterator

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Iterator<E> descendingIterator ()
```

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

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Iterator<E>` | an iterator over the elements in this set in descending order <br /> |

### descendingSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public NavigableSet<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://developer.android.com/reference/java/util/Collections#reverseOrder(java.util.Comparator<T>)``(comparator())`.
The expression `s.descendingSet().descendingSet()` returns a
view of `s` essentially equivalent to `s`.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/NavigableSet<E>` | a reverse order view of this set <br /> |

### equals

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public boolean equals (Object 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.

<br />

| Parameters ||
|---|---|
| `o` | `Object`: the object to be compared for equality with this set <br /> |

| Returns ||
|---|---|
| `boolean` | `true` if the specified object is equal to this set <br /> |

### first

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public E first ()
```

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

<br />

| Returns ||
|---|---|
| `E` | the first (lowest) element currently in this set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/util/NoSuchElementException` |   |

### floor

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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.

<br />

| Parameters ||
|---|---|
| `e` | `E`: the value to match <br /> |

| Returns ||
|---|---|
| `E` | the greatest element less than or equal to `e`, or `null` if there is no such element <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null |

### headSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public NavigableSet<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.

<br />

| Parameters ||
|---|---|
| `toElement` | `E`: high endpoint of the returned set <br /> |
| `inclusive` | `boolean`: `true` if the high endpoint is to be included in the returned view <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/NavigableSet<E>` | a view of the portion of this set whose elements are less than (or equal to, if `inclusive` is true) `toElement` <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if `toElement` is null |

### headSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public NavigableSet<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)`.

<br />

| Parameters ||
|---|---|
| `toElement` | `E`: high endpoint (exclusive) of the returned set <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/NavigableSet<E>` | a view of the portion of this set whose elements are strictly less than `toElement` <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if `toElement` is null |

### higher

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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.

<br />

| Parameters ||
|---|---|
| `e` | `E`: the value to match <br /> |

| Returns ||
|---|---|
| `E` | the least element greater than `e`, or `null` if there is no such element <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null |

### isEmpty

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public boolean isEmpty ()
```

Returns `true` if this set contains no elements.

<br />

| Returns ||
|---|---|
| `boolean` | `true` if this set contains no elements <br /> |

### iterator

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Iterator<E> iterator ()
```

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

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Iterator<E>` | an iterator over the elements in this set in ascending order <br /> |

### last

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public E last ()
```

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

<br />

| Returns ||
|---|---|
| `E` | the last (highest) element currently in this set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/util/NoSuchElementException` |   |

### lower

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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.

<br />

| Parameters ||
|---|---|
| `e` | `E`: the value to match <br /> |

| Returns ||
|---|---|
| `E` | the greatest element less than `e`, or `null` if there is no such element <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null |

### pollFirst

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public E pollFirst ()
```

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

<br />

| Returns ||
|---|---|
| `E` | the first element, or `null` if this set is empty <br /> |

### pollLast

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public E pollLast ()
```

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

<br />

| Returns ||
|---|---|
| `E` | the last element, or `null` if this set is empty <br /> |

### remove

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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.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.)

<br />

| Parameters ||
|---|---|
| `o` | `Object`: object to be removed from this set, if present <br /> |

| Returns ||
|---|---|
| `boolean` | `true` if this set contained the specified element <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` | if `o` cannot be compared with the elements currently in this set |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null |

### removeAll

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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.

<br />

| Parameters ||
|---|---|
| `c` | `Collection`: collection containing elements to be removed from this set <br /> |

| Returns ||
|---|---|
| `boolean` | `true` if this set changed as a result of the call <br /> |

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

### size

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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`.

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.

<br />

| Returns ||
|---|---|
| `int` | the number of elements in this set <br /> |

### spliterator

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Spliterator<E> spliterator ()
```

Returns a `https://developer.android.com/reference/java/util/Spliterator` over the elements in this set.

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

The [spliterator's comparator](https://developer.android.com/reference/java/util/Spliterator#getComparator())
is `null` if the [set's comparator](https://developer.android.com/reference/java/util/concurrent/ConcurrentSkipListSet#comparator())
is `null`.
Otherwise, the spliterator's comparator is the same as or imposes the
same total ordering as the set's comparator.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Spliterator<E>` | a `Spliterator` over the elements in this set <br /> |

### subSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public NavigableSet<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.

<br />

| Parameters ||
|---|---|
| `fromElement` | `E`: low endpoint of the returned set <br /> |
| `fromInclusive` | `boolean`: `true` if the low endpoint is to be included in the returned view <br /> |
| `toElement` | `E`: high endpoint of the returned set <br /> |
| `toInclusive` | `boolean`: `true` if the high endpoint is to be included in the returned view <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/NavigableSet<E>` | a view of the portion of this set whose elements range from `fromElement`, inclusive, to `toElement`, exclusive <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if `fromElement` or `toElement` is null |

### subSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public NavigableSet<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)`.

<br />

| Parameters ||
|---|---|
| `fromElement` | `E`: low endpoint (inclusive) of the returned set <br /> |
| `toElement` | `E`: high endpoint (exclusive) of the returned set <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/NavigableSet<E>` | a view of the portion of this set whose elements range from `fromElement`, inclusive, to `toElement`, exclusive <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if `fromElement` or `toElement` is null |

### tailSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public NavigableSet<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.

<br />

| Parameters ||
|---|---|
| `fromElement` | `E`: low endpoint of the returned set <br /> |
| `inclusive` | `boolean`: `true` if the low endpoint is to be included in the returned view <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/NavigableSet<E>` | a view of the portion of this set whose elements are greater than or equal to `fromElement` <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if `fromElement` is null |

### tailSet

Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public NavigableSet<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)`.

<br />

| Parameters ||
|---|---|
| `fromElement` | `E`: low endpoint (inclusive) of the returned set <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/NavigableSet<E>` | a view of the portion of this set whose elements are greater than or equal to `fromElement` <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` |   |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` |   |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if `fromElement` is null |