public class HashSet<T> extends AbstractSet<T> implements Set<T>, Cloneable
Most operations are O(1), assuming no hash collisions. In the worst case (where all hashes collide), operations are O(n). Setting the initial capacity too low will force many resizing operations, but setting the initial capacity too high (or loadfactor too low) leads to wasted memory and slower iteration.
HashSet accepts the null key and null values. It is not synchronized,
so if you need multi-threaded access, consider using:
Set s = Collections.synchronizedSet(new HashSet(...));
The iterators are fail-fast, meaning that any structural
modification, except for remove() called on the iterator
itself, cause the iterator to throw a
ConcurrentModificationException rather than exhibit
non-deterministic behavior.
Collection,
Set,
TreeSet,
Collections.synchronizedSet(Set),
HashMap,
LinkedHashSet| Constructor and Description |
|---|
HashSet()
Construct a new, empty HashSet whose backing HashMap has the default
capacity (11) and loadFacor (0.75).
|
HashSet(Collection<? extends T> c)
Construct a new HashSet with the same elements as are in the supplied
collection (eliminating any duplicates, of course).
|
HashSet(int initialCapacity)
Construct a new, empty HashSet whose backing HashMap has the supplied
capacity and the default load factor (0.75).
|
HashSet(int initialCapacity,
float loadFactor)
Construct a new, empty HashSet whose backing HashMap has the supplied
capacity and load factor.
|
| Modifier and Type | Method and Description |
|---|---|
boolean |
add(T o)
Adds the given Object to the set if it is not already in the Set.
|
void |
clear()
Empties this Set of all elements; this takes constant time.
|
Object |
clone()
Returns a shallow copy of this Set.
|
boolean |
contains(Object o)
Returns true if the supplied element is in this Set.
|
boolean |
isEmpty()
Returns true if this set has no elements in it.
|
Iterator<T> |
iterator()
Returns an Iterator over the elements of this Set, which visits the
elements in no particular order.
|
boolean |
remove(Object o)
Removes the supplied Object from this Set if it is in the Set.
|
int |
size()
Returns the number of elements in this Set (its cardinality).
|
equals, hashCode, removeAlladdAll, containsAll, retainAll, toArray, toArray, toStringpublic HashSet()
public HashSet(Collection<? extends T> c)
c - a collection of initial set elementsNullPointerException - if c is nullpublic HashSet(int initialCapacity)
initialCapacity - the initial capacity of the backing HashMapIllegalArgumentException - if the capacity is negativepublic HashSet(int initialCapacity,
float loadFactor)
initialCapacity - the initial capacity of the backing HashMaploadFactor - the load factor of the backing HashMapIllegalArgumentException - if either argument is negative, or
if loadFactor is POSITIVE_INFINITY or NaNpublic boolean add(T o)
add in interface Collection<T>add in interface Set<T>add in class AbstractCollection<T>o - the Object to add to this Setpublic void clear()
clear in interface Collection<T>clear in interface Set<T>clear in class AbstractCollection<T>Iterator.remove()public Object clone()
public boolean contains(Object o)
contains in interface Collection<T>contains in interface Set<T>contains in class AbstractCollection<T>o - the Object to look forpublic boolean isEmpty()
isEmpty in interface Collection<T>isEmpty in interface Set<T>isEmpty in class AbstractCollection<T>size() == 0.AbstractCollection.size()public Iterator<T> iterator()
iterator in interface Iterable<T>iterator in interface Collection<T>iterator in interface Set<T>iterator in class AbstractCollection<T>ConcurrentModificationExceptionpublic boolean remove(Object o)
remove in interface Collection<T>remove in interface Set<T>remove in class AbstractCollection<T>o - the object to removeIterator.remove()public int size()
size in interface Collection<T>size in interface Set<T>size in class AbstractCollection<T>