# HashSet Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary:[Ctors](https://developer.android.com/reference/java/util/HashSet#pubctors)\|[Methods](https://developer.android.com/reference/java/util/HashSet#pubmethods)\|[Inherited Methods](https://developer.android.com/reference/java/util/HashSet#inhmethods) # HashSet ` public class HashSet ` ` `` `` extends `[AbstractSet](https://developer.android.com/reference/java/util/AbstractSet)` `` implements `[Cloneable](https://developer.android.com/reference/java/lang/Cloneable)`, `[Serializable](https://developer.android.com/reference/java/io/Serializable)`, `[Set](https://developer.android.com/reference/java/util/Set)` ` |---|---|---|------------------------| | [java.lang.Object](https://developer.android.com/reference/java/lang/Object) |||| | ↳ | [java.util.AbstractCollection](https://developer.android.com/reference/java/util/AbstractCollection)\ ||| | | ↳ | [java.util.AbstractSet](https://developer.android.com/reference/java/util/AbstractSet)\ || | | | ↳ | java.util.HashSet\ | |-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Known direct subclasses [LinkedHashSet](https://developer.android.com/reference/java/util/LinkedHashSet)\ |---------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------| | [LinkedHashSet](https://developer.android.com/reference/java/util/LinkedHashSet)\ | Hash table and linked list implementation of the`Set`interface, with well-defined encounter order. | |
*** ** * ** *** This class implements the`Set`interface, backed by a hash table (actually a`HashMap`instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the`null`element. This class offers constant time performance for the basic operations (`add`,`remove`,`contains`and`size`), assuming the hash function disperses the elements properly among the buckets. Iterating over this set requires time proportional to the sum of the`HashSet`instance's size (the number of elements) plus the "capacity" of the backing`HashMap`instance (the number of buckets). Thus, it's very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important. **Note that this implementation is not synchronized.** If multiple threads access a hash set concurrently, and at least one of the threads modifies the set, it*must* be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the set. If no such object exists, the set should be "wrapped" using the[Collections.synchronizedSet](https://developer.android.com/reference/java/util/Collections#synchronizedSet(java.util.Set))method. This is best done at creation time, to prevent accidental unsynchronized access to the set: ``` Set s = Collections.synchronizedSet(new HashSet(...)); ``` The iterators returned by this class's`iterator`method are*fail-fast* : if the set is modified at any time after the iterator is created, in any way except through the iterator's own`remove`method, the Iterator throws a[ConcurrentModificationException](https://developer.android.com/reference/java/util/ConcurrentModificationException). Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future. Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw`ConcurrentModificationException`on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness:*the fail-fast behavior of iterators should be used only to detect bugs.* This class is a member of the[Java Collections Framework](https://reference/java/util/package-summary.html#CollectionsFramework). **See also:** - [Collection](https://developer.android.com/reference/java/util/Collection) - [Set](https://developer.android.com/reference/java/util/Set) - [TreeSet](https://developer.android.com/reference/java/util/TreeSet) - [HashMap](https://developer.android.com/reference/java/util/HashMap) ## Summary | ### Public constructors || |--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---| | ` `[HashSet](https://developer.android.com/reference/java/util/HashSet#HashSet())`() ` Constructs a new, empty set; the backing`HashMap`instance has default initial capacity (16) and load factor (0.75). | | ` `[HashSet](https://developer.android.com/reference/java/util/HashSet#HashSet(int))`(int initialCapacity) ` Constructs a new, empty set; the backing`HashMap`instance has the specified initial capacity and default load factor (0.75). | | ` `[HashSet](https://developer.android.com/reference/java/util/HashSet#HashSet(int,%20float))`(int initialCapacity, float loadFactor) ` Constructs a new, empty set; the backing`HashMap`instance has the specified initial capacity and the specified load factor. | | ` `[HashSet](https://developer.android.com/reference/java/util/HashSet#HashSet(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Constructs a new set containing the elements in the specified collection. | | ### Public methods || |-----------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` boolean` | ` `[add](https://developer.android.com/reference/java/util/HashSet#add(E))`(E e) ` Adds the specified element to this set if it is not already present. | | ` void` | ` `[clear](https://developer.android.com/reference/java/util/HashSet#clear())`() ` Removes all of the elements from this set. | | ` `[Object](https://developer.android.com/reference/java/lang/Object) | ` `[clone](https://developer.android.com/reference/java/util/HashSet#clone())`() ` Returns a shallow copy of this`HashSet`instance: the elements themselves are not cloned. | | ` boolean` | ` `[contains](https://developer.android.com/reference/java/util/HashSet#contains(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Returns`true`if this set contains the specified element. | | ` boolean` | ` `[isEmpty](https://developer.android.com/reference/java/util/HashSet#isEmpty())`() ` Returns`true`if this set contains no elements. | | ` `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/util/HashSet#iterator())`() ` Returns an iterator over the elements in this set. | | ` static `[HashSet](https://developer.android.com/reference/java/util/HashSet)`` | ` `[newHashSet](https://developer.android.com/reference/java/util/HashSet#newHashSet(int))`(int numElements) ` Creates a new, empty HashSet suitable for the expected number of elements. | | ` boolean` | ` `[remove](https://developer.android.com/reference/java/util/HashSet#remove(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Removes the specified element from this set if it is present. | | ` int` | ` `[size](https://developer.android.com/reference/java/util/HashSet#size())`() ` Returns the number of elements in this set (its cardinality). | | ` `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/util/HashSet#spliterator())`() ` Creates a*[late-binding](https://developer.android.com/reference/java/util/Spliterator#binding)* and*fail-fast* [Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements in this set. | | ` T[]` | ` `[toArray](https://developer.android.com/reference/java/util/HashSet#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. | | ` `[Object[]](https://developer.android.com/reference/java/lang/Object) | ` `[toArray](https://developer.android.com/reference/java/util/HashSet#toArray())`() ` Returns an array containing all of the elements in this collection. | | ### Inherited methods | |-----------------------|---| | From class` `[java.util.AbstractSet](https://developer.android.com/reference/java/util/AbstractSet)` ` |------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` boolean` | ` `[equals](https://developer.android.com/reference/java/util/AbstractSet#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Compares the specified object with this set for equality. | | ` int` | ` `[hashCode](https://developer.android.com/reference/java/util/AbstractSet#hashCode())`() ` Returns the hash code value for this set. | | ` boolean` | ` `[removeAll](https://developer.android.com/reference/java/util/AbstractSet#removeAll(java.util.Collection))`(`[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` `[java.util.AbstractCollection](https://developer.android.com/reference/java/util/AbstractCollection)` ` |-----------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` boolean` | ` `[add](https://developer.android.com/reference/java/util/AbstractCollection#add(E))`(E e) ` Ensures that this collection contains the specified element (optional operation). | | ` boolean` | ` `[addAll](https://developer.android.com/reference/java/util/AbstractCollection#addAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Adds all of the elements in the specified collection to this collection (optional operation). | | ` void` | ` `[clear](https://developer.android.com/reference/java/util/AbstractCollection#clear())`() ` Removes all of the elements from this collection (optional operation). | | ` boolean` | ` `[contains](https://developer.android.com/reference/java/util/AbstractCollection#contains(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Returns`true`if this collection contains the specified element. | | ` boolean` | ` `[containsAll](https://developer.android.com/reference/java/util/AbstractCollection#containsAll(java.util.Collection))`(`[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` | ` `[isEmpty](https://developer.android.com/reference/java/util/AbstractCollection#isEmpty())`() ` Returns`true`if this collection contains no elements. | | ` abstract `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/util/AbstractCollection#iterator())`() ` Returns an iterator over the elements contained in this collection. | | ` boolean` | ` `[remove](https://developer.android.com/reference/java/util/AbstractCollection#remove(java.lang.Object))`(`[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` | ` `[removeAll](https://developer.android.com/reference/java/util/AbstractCollection#removeAll(java.util.Collection))`(`[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` | ` `[retainAll](https://developer.android.com/reference/java/util/AbstractCollection#retainAll(java.util.Collection))`(`[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` | ` `[size](https://developer.android.com/reference/java/util/AbstractCollection#size())`() ` Returns the number of elements in this collection. | | ` T[]` | ` `[toArray](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. | | ` `[Object[]](https://developer.android.com/reference/java/lang/Object) | ` `[toArray](https://developer.android.com/reference/java/util/AbstractCollection#toArray())`() ` Returns an array containing all of the elements in this collection. | | ` `[String](https://developer.android.com/reference/java/lang/String) | ` `[toString](https://developer.android.com/reference/java/util/AbstractCollection#toString())`() ` Returns a string representation of this collection. | || | From class` `[java.lang.Object](https://developer.android.com/reference/java/lang/Object)` ` |--------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` `[Object](https://developer.android.com/reference/java/lang/Object) | ` `[clone](https://developer.android.com/reference/java/lang/Object#clone())`() ` Creates and returns a copy of this object. | | ` boolean` | ` `[equals](https://developer.android.com/reference/java/lang/Object#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` obj) ` Indicates whether some other object is "equal to" this one. | | ` void` | ` `[finalize](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 `[Class](https://developer.android.com/reference/java/lang/Class)`` | ` `[getClass](https://developer.android.com/reference/java/lang/Object#getClass())`() ` Returns the runtime class of this`Object`. | | ` int` | ` `[hashCode](https://developer.android.com/reference/java/lang/Object#hashCode())`() ` Returns a hash code value for the object. | | ` final void` | ` `[notify](https://developer.android.com/reference/java/lang/Object#notify())`() ` Wakes up a single thread that is waiting on this object's monitor. | | ` final void` | ` `[notifyAll](https://developer.android.com/reference/java/lang/Object#notifyAll())`() ` Wakes up all threads that are waiting on this object's monitor. | | ` `[String](https://developer.android.com/reference/java/lang/String) | ` `[toString](https://developer.android.com/reference/java/lang/Object#toString())`() ` Returns a string representation of the object. | | ` final void` | ` `[wait](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` | ` `[wait](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` | ` `[wait](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` `[java.util.Set](https://developer.android.com/reference/java/util/Set)` ` |----------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` abstract boolean` | ` `[add](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` | ` `[addAll](https://developer.android.com/reference/java/util/Set#addAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` 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://developer.android.com/reference/java/util/Set#clear())`() ` Removes all of the elements from this set (optional operation). | | ` abstract boolean` | ` `[contains](https://developer.android.com/reference/java/util/Set#contains(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Returns`true`if this set contains the specified element. | | ` abstract boolean` | ` `[containsAll](https://developer.android.com/reference/java/util/Set#containsAll(java.util.Collection))`(`[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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[copyOf](https://developer.android.com/reference/java/util/Set#copyOf(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` coll) ` Returns an[unmodifiable Set](https://developer.android.com/reference/java/util/HashSet#unmodifiable)containing the elements of the given Collection. | | ` abstract boolean` | ` `[equals](https://developer.android.com/reference/java/util/Set#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Compares the specified object with this set for equality. | | ` abstract int` | ` `[hashCode](https://developer.android.com/reference/java/util/Set#hashCode())`() ` Returns the hash code value for this set. | | ` abstract boolean` | ` `[isEmpty](https://developer.android.com/reference/java/util/Set#isEmpty())`() ` Returns`true`if this set contains no elements. | | ` abstract `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/util/Set#iterator())`() ` Returns an iterator over the elements in this set. | | ` static `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](https://developer.android.com/reference/java/util/Set#of(E[]))`(E... elements) ` Returns an unmodifiable set containing an arbitrary number of elements. | | ` static `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](https://developer.android.com/reference/java/util/Set#of())`() ` Returns an unmodifiable set containing zero elements. | | ` static `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](https://developer.android.com/reference/java/util/Set#of(E,%20E))`(E e1, E e2) ` Returns an unmodifiable set containing two elements. | | ` static `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](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 `[Set](https://developer.android.com/reference/java/util/Set)`` | ` `[of](https://developer.android.com/reference/java/util/Set#of(E))`(E e1) ` Returns an unmodifiable set containing one element. | | ` abstract boolean` | ` `[remove](https://developer.android.com/reference/java/util/Set#remove(java.lang.Object))`(`[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` | ` `[removeAll](https://developer.android.com/reference/java/util/Set#removeAll(java.util.Collection))`(`[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` | ` `[retainAll](https://developer.android.com/reference/java/util/Set#retainAll(java.util.Collection))`(`[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` | ` `[size](https://developer.android.com/reference/java/util/Set#size())`() ` Returns the number of elements in this set (its cardinality). | | ` default `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/util/Set#spliterator())`() ` Creates a`Spliterator`over the elements in this set. | | ` abstract `[Object[]](https://developer.android.com/reference/java/lang/Object) | ` `[toArray](https://developer.android.com/reference/java/util/Set#toArray())`() ` Returns an array containing all of the elements in this set. | | ` abstract T[]` | ` `[toArray](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` `[java.util.Collection](https://developer.android.com/reference/java/util/Collection)` ` |----------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` abstract boolean` | ` `[add](https://developer.android.com/reference/java/util/Collection#add(E))`(E e) ` Ensures that this collection contains the specified element (optional operation). | | ` abstract boolean` | ` `[addAll](https://developer.android.com/reference/java/util/Collection#addAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Adds all of the elements in the specified collection to this collection (optional operation). | | ` abstract void` | ` `[clear](https://developer.android.com/reference/java/util/Collection#clear())`() ` Removes all of the elements from this collection (optional operation). | | ` abstract boolean` | ` `[contains](https://developer.android.com/reference/java/util/Collection#contains(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Returns`true`if this collection contains the specified element. | | ` abstract boolean` | ` `[containsAll](https://developer.android.com/reference/java/util/Collection#containsAll(java.util.Collection))`(`[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` | ` `[equals](https://developer.android.com/reference/java/util/Collection#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Compares the specified object with this collection for equality. | | ` abstract int` | ` `[hashCode](https://developer.android.com/reference/java/util/Collection#hashCode())`() ` Returns the hash code value for this collection. | | ` abstract boolean` | ` `[isEmpty](https://developer.android.com/reference/java/util/Collection#isEmpty())`() ` Returns`true`if this collection contains no elements. | | ` abstract `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/util/Collection#iterator())`() ` Returns an iterator over the elements in this collection. | | ` default `[Stream](https://developer.android.com/reference/java/util/stream/Stream)`` | ` `[parallelStream](https://developer.android.com/reference/java/util/Collection#parallelStream())`() ` Returns a possibly parallel`Stream`with this collection as its source. | | ` abstract boolean` | ` `[remove](https://developer.android.com/reference/java/util/Collection#remove(java.lang.Object))`(`[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` | ` `[removeAll](https://developer.android.com/reference/java/util/Collection#removeAll(java.util.Collection))`(`[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` | ` `[removeIf](https://developer.android.com/reference/java/util/Collection#removeIf(java.util.function.Predicate))`(`[Predicate](https://developer.android.com/reference/java/util/function/Predicate)` filter) ` Removes all of the elements of this collection that satisfy the given predicate. | | ` abstract boolean` | ` `[retainAll](https://developer.android.com/reference/java/util/Collection#retainAll(java.util.Collection))`(`[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` | ` `[size](https://developer.android.com/reference/java/util/Collection#size())`() ` Returns the number of elements in this collection. | | ` default `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/util/Collection#spliterator())`() ` Creates a[Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements in this collection. | | ` default `[Stream](https://developer.android.com/reference/java/util/stream/Stream)`` | ` `[stream](https://developer.android.com/reference/java/util/Collection#stream())`() ` Returns a sequential`Stream`with this collection as its source. | | ` abstract T[]` | ` `[toArray](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 `[Object[]](https://developer.android.com/reference/java/lang/Object) | ` `[toArray](https://developer.android.com/reference/java/util/Collection#toArray())`() ` Returns an array containing all of the elements in this collection. | | ` default T[]` | ` `[toArray](https://developer.android.com/reference/java/util/Collection#toArray(java.util.function.IntFunction))`(`[IntFunction](https://developer.android.com/reference/java/util/function/IntFunction)` generator) ` Returns an array containing all of the elements in this collection, using the provided`generator`function to allocate the returned array. | || | From interface` `[java.lang.Iterable](https://developer.android.com/reference/java/lang/Iterable)` ` |----------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` default void` | ` `[forEach](https://developer.android.com/reference/java/lang/Iterable#forEach(java.util.function.Consumer))`(`[Consumer](https://developer.android.com/reference/java/util/function/Consumer)` 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://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/lang/Iterable#iterator())`() ` Returns an iterator over elements of type`T`. | | ` default `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/lang/Iterable#spliterator())`() ` Creates a[Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements described by this`Iterable`. | || ## Public constructors ### HashSet Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public HashSet () ``` Constructs a new, empty set; the backing`HashMap`instance has default initial capacity (16) and load factor (0.75).
### HashSet Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public HashSet (int initialCapacity) ``` Constructs a new, empty set; the backing`HashMap`instance has the specified initial capacity and default load factor (0.75).
##### API Note: - To create a`HashSet`with an initial capacity that accommodates an expected number of elements, use[newHashSet](https://developer.android.com/reference/java/util/HashSet#newHashSet(int)). | Parameters || |-------------------|------------------------------------------------------| | `initialCapacity` | `int`: the initial capacity of the hash table
| | Throws || |--------------------------------------------------------------------------------------------------------|-------------------------------------------| | [IllegalArgumentException](https://developer.android.com/reference/java/lang/IllegalArgumentException) | if the initial capacity is less than zero | ### HashSet Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public HashSet (int initialCapacity, float loadFactor) ``` Constructs a new, empty set; the backing`HashMap`instance has the specified initial capacity and the specified load factor.
##### API Note: - To create a`HashSet`with an initial capacity that accommodates an expected number of elements, use[newHashSet](https://developer.android.com/reference/java/util/HashSet#newHashSet(int)). | Parameters || |-------------------|----------------------------------------------------| | `initialCapacity` | `int`: the initial capacity of the hash map
| | `loadFactor` | `float`: the load factor of the hash map
| | Throws || |--------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------| | [IllegalArgumentException](https://developer.android.com/reference/java/lang/IllegalArgumentException) | if the initial capacity is less than zero, or if the load factor is nonpositive | ### HashSet Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public HashSet (Collection c) ``` Constructs a new set containing the elements in the specified collection. The`HashMap`is created with default load factor (0.75) and an initial capacity sufficient to contain the elements in the specified collection.
| Parameters || |-----|-----------------------------------------------------------------------------------| | `c` | `Collection`: the collection whose elements are to be placed into this set
| | Throws || |------------------------------------------------------------------------------------------------|-------------------------------------| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified collection is null | ## Public methods ### add Added in[API level 1](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 this set contains no element`e2`such that`Objects.equals(e, e2)`. If this set already contains the element, the call leaves the set unchanged and returns`false`.
| Parameters || |-----|---------------------------------------------| | `e` | `E`: element to be added to this set
| | Returns || |-----------|------------------------------------------------------------------------| | `boolean` | `true`if this set did not already contain the specified element
| ### clear Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public void clear () ``` Removes all of the elements from this set. The set will be empty after this call returns.
### clone Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public Object clone () ``` Returns a shallow copy of this`HashSet`instance: the elements themselves are not cloned.
| Returns || |--------------------------------------------------------------------|-----------------------------------| | [Object](https://developer.android.com/reference/java/lang/Object) | a shallow copy of this set
| ### contains Added in[API level 1](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`Objects.equals(o, e)`.
| Parameters || |-----|---------------------------------------------------------------------| | `o` | `Object`: element whose presence in this set is to be tested
| | Returns || |-----------|---------------------------------------------------------| | `boolean` | `true`if this set contains the specified element
| ### isEmpty Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean isEmpty () ``` Returns`true`if this set contains no elements.
| Returns || |-----------|-----------------------------------------------| | `boolean` | `true`if this set contains no elements
| ### iterator Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public Iterator iterator () ``` Returns an iterator over the elements in this set. The elements are returned in no particular order.
| Returns || |-----------------------------------------------------------------------------|--------------------------------------------------| | [Iterator](https://developer.android.com/reference/java/util/Iterator)`` | an Iterator over the elements in this set
| **See also:** - [ConcurrentModificationException](https://developer.android.com/reference/java/util/ConcurrentModificationException) ### newHashSet Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public static HashSet newHashSet (int numElements) ``` Creates a new, empty HashSet suitable for the expected number of elements. The returned set uses the default load factor of 0.75, and its initial capacity is generally large enough so that the expected number of elements can be added without resizing the set.
| Parameters || |---------------|-----------------------------------------------| | `numElements` | `int`: the expected number of elements
| | Returns || |---------------------------------------------------------------------------|------------------------------| | [HashSet](https://developer.android.com/reference/java/util/HashSet)`` | the newly created set
| | Throws || |--------------------------------------------------------------------------------------------------------|----------------------------| | [IllegalArgumentException](https://developer.android.com/reference/java/lang/IllegalArgumentException) | if numElements is negative | ### remove Added in[API level 1](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`Objects.equals(o, 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`: object to be removed from this set, if present
| | Returns || |-----------|---------------------------------------------------------| | `boolean` | `true`if the set contained the specified element
| ### size Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public int size () ``` Returns the number of elements in this set (its cardinality).
| Returns || |-------|-------------------------------------------------------------| | `int` | the number of elements in this set (its cardinality)
| ### spliterator Added in[API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public Spliterator spliterator () ``` Creates a*[late-binding](https://developer.android.com/reference/java/util/Spliterator#binding)* and*fail-fast* [Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements in this set. The`Spliterator`reports[Spliterator.SIZED](https://developer.android.com/reference/java/util/Spliterator#SIZED)and[Spliterator.DISTINCT](https://developer.android.com/reference/java/util/Spliterator#DISTINCT). Overriding implementations should document the reporting of additional characteristic values.
| Returns || |-----------------------------------------------------------------------------------|----------------------------------------------------| | [Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | a`Spliterator`over the elements in this set
| ### toArray Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public T[] toArray (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. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection. If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to`null`. (This is useful in determining the length of this collection*only* if the caller knows that this collection does not contain any`null`elements.) If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
| Parameters || |-----|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `a` | `T`: the array into which the elements of this collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
| | Returns || |-------|-------------------------------------------------------------------| | `T[]` | an array containing all of the elements in this collection
| ### toArray Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public Object[] toArray () ``` Returns an array containing all of the elements in this collection. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array's[runtime component type](https://developer.android.com/reference/java/lang/Class#getComponentType())is`Object`. The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.
| Returns || |----------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [Object[]](https://developer.android.com/reference/java/lang/Object) | an array, whose[type](https://developer.android.com/reference/java/lang/Class#getComponentType())is`Object`, containing all of the elements in this collection
|