HashSet
open class HashSet<E : Any!> : AbstractSet<E>, Cloneable, Serializable, MutableSet<E>
|
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
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
. 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.
Summary
Public constructors | |
---|---|
HashSet() Constructs a new, empty set; the backing |
|
Constructs a new, empty set; the backing |
|
Constructs a new, empty set; the backing |
|
HashSet(c: MutableCollection<out E>) Constructs a new set containing the elements in the specified collection. |
Public methods | |
---|---|
open Boolean |
add(element: E) Adds the specified element to this set if it is not already present. |
open Unit |
clear() Removes all of the elements from this set. |
open Any |
clone() Returns a shallow copy of this |
open Boolean |
contains(element: E) Returns |
open Boolean |
contains(element: E) Returns |
open Boolean |
isEmpty() Returns |
open MutableIterator<E> |
iterator() Returns an iterator over the elements in this set. |
open static HashSet<T> |
newHashSet(numElements: Int) Creates a new, empty HashSet suitable for the expected number of elements. |
open Boolean |
remove(element: E) Removes the specified element from this set if it is present. |
open Boolean |
remove(element: E) Removes the specified element from this set if it is present. |
open Spliterator<E> |
Creates a late-binding and fail-fast |
open Array<Any!> |
toArray() |
open Array<T> |
Inherited functions | |||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|||||||||||||||||||||||||
|
Public constructors
HashSet
HashSet()
Constructs a new, empty set; the backing HashMap
instance has default initial capacity (16) and load factor (0.75).
HashSet
HashSet(initialCapacity: Int)
Constructs a new, empty set; the backing HashMap
instance has the specified initial capacity and default load factor (0.75).
Parameters | |
---|---|
initialCapacity |
Int: the initial capacity of the hash table |
Exceptions | |
---|---|
java.lang.IllegalArgumentException |
if the initial capacity is less than zero |
HashSet
HashSet(
initialCapacity: Int,
loadFactor: Float)
Constructs a new, empty set; the backing HashMap
instance has the specified initial capacity and the specified load factor.
Parameters | |
---|---|
initialCapacity |
Int: the initial capacity of the hash map |
loadFactor |
Float: the load factor of the hash map |
Exceptions | |
---|---|
java.lang.IllegalArgumentException |
if the initial capacity is less than zero, or if the load factor is nonpositive |
HashSet
HashSet(c: MutableCollection<out E>)
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 |
MutableCollection<out E>: the collection whose elements are to be placed into this set |
Exceptions | |
---|---|
java.lang.NullPointerException |
if the specified collection is null |
Public methods
add
open fun add(element: E): Boolean
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 |
element to be added to this set |
Return | |
---|---|
Boolean |
true if this set did not already contain the specified element |
Exceptions | |
---|---|
java.lang.UnsupportedOperationException |
if the add operation is not supported by this set |
java.lang.ClassCastException |
if the class of the specified element prevents it from being added to this set |
java.lang.NullPointerException |
if the specified element is null and this set does not permit null elements |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this set |
java.lang.IllegalStateException |
if the element cannot be added at this time due to insertion restrictions |
clear
open fun clear(): Unit
Removes all of the elements from this set. The set will be empty after this call returns.
Exceptions | |
---|---|
java.lang.UnsupportedOperationException |
if the clear method is not supported by this set |
clone
open fun clone(): Any
Returns a shallow copy of this HashSet
instance: the elements themselves are not cloned.
Return | |
---|---|
Any |
a shallow copy of this set |
Exceptions | |
---|---|
java.lang.CloneNotSupportedException |
if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned. |
contains
open fun contains(element: E): Boolean
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 |
element whose presence in this set is to be tested |
Return | |
---|---|
Boolean |
true if this set contains the specified element |
contains
open fun contains(element: E): Boolean
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 |
element whose presence in this set is to be tested |
Return | |
---|---|
Boolean |
true if this set contains the specified element |
isEmpty
open fun isEmpty(): Boolean
Returns true
if this set contains no elements.
Return | |
---|---|
Boolean |
true if this set contains no elements |
iterator
open fun iterator(): MutableIterator<E>
Returns an iterator over the elements in this set. The elements are returned in no particular order.
Return | |
---|---|
MutableIterator<E> |
an Iterator over the elements in this set |
newHashSet
open static fun <T : Any!> newHashSet(numElements: Int): HashSet<T>
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 |
<T> |
the type of elements maintained by the new set |
Return | |
---|---|
HashSet<T> |
the newly created set |
Exceptions | |
---|---|
java.lang.IllegalArgumentException |
if numElements is negative |
remove
open fun remove(element: E): Boolean
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 to be removed from this set, if present |
Return | |
---|---|
Boolean |
true if the set contained the specified element |
Exceptions | |
---|---|
java.lang.ClassCastException |
if the type of the specified element is incompatible with this set (optional) |
java.lang.NullPointerException |
if the specified element is null and this set does not permit null elements (optional) |
java.lang.UnsupportedOperationException |
if the remove operation is not supported by this set |
remove
open fun remove(element: E): Boolean
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 to be removed from this set, if present |
Return | |
---|---|
Boolean |
true if the set contained the specified element |
Exceptions | |
---|---|
java.lang.ClassCastException |
if the type of the specified element is incompatible with this set (optional) |
java.lang.NullPointerException |
if the specified element is null and this set does not permit null elements (optional) |
java.lang.UnsupportedOperationException |
if the remove operation is not supported by this set |
spliterator
open fun spliterator(): Spliterator<E>
Creates a late-binding and fail-fast Spliterator
over the elements in this set.
The Spliterator
reports Spliterator.SIZED
and Spliterator.DISTINCT
. Overriding implementations should document the reporting of additional characteristic values.
Return | |
---|---|
Spliterator<E> |
a Spliterator over the elements in this set |
toArray
open fun <T : Any!> toArray(a: Array<T>): Array<T>
Parameters | |
---|---|
<T> |
the component type of the array to contain the collection |
a |
Array<T>: the array into which the elements of this set are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose. |
Return | |
---|---|
Array<T> |
an array containing all the elements in this set |
Exceptions | |
---|---|
java.lang.ArrayStoreException |
if the runtime type of the specified array is not a supertype of the runtime type of every element in this set |
java.lang.NullPointerException |
if the specified array is null |
Properties
size
open val size: Int
Returns the number of elements in this set (its cardinality).
Return | |
---|---|
Int |
the number of elements in this set (its cardinality) |