class HashSet<E> in Java

Компьютер, программы

→

Java

→

Java (class, interface, collections, etc.)

class HashSet in Java

посмотрели 328 раз

обновлено: 25 Augusta 2026

class HashSet<E> implements interface Set<E>

HashSet contains a non-repeating collection of items.
HashSet contains unsorted items.
HashSet allows you to quickly determine whether such an element exists or not (fast because it uses an index that is calculated from the hash code of the element).
HashSet has methods Add, Remove, Contains, but because it uses a hash implementation, these operations take 1 action (the Contains and Remove methods in ArrayList take n actions.)

HashSet is not synchronized. If multiple threads access a hash set concurrently, and at least one of the threads modifies the HashSet, it must be synchronized externally. This is typically accomplished by synchronizing using the Collections.synchronizedSet method:

Java

Set mySet1 = Collections.synchronizedSet( new HashSet(...) );

Java

class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, Serializable
{
     // Constructors
     HashSet()
     HashSet(Collection<? extends E> c)
     HashSet(int initialCapacity)
     HashSet(int initialCapacity, float loadFactor)

     // Methods
     boolean add(E e)
     void clear()
     Object clone()
     boolean contains(Object o)
     boolean isEmpty()
     Iterator<E> iterator()
     boolean remove(Object o)
     int size()
     Spliterator<E> spliterator()

     // Methods inherited from class java.util.AbstractSet
     boolean equals(Object o)
     int hashCode()
     boolean removeAll(Collection<?> c)

     // Methods inherited from class java.util.AbstractCollection
     boolean addAll(Collection<? extends E> c)
     boolean containsAll(Collection<?> c)
     boolean retainAll(Collection<?> c)
     Object[] toArray()
     <T> T[] toArray(T[] a)
     String toString()

     // Methods inherited from class java.lang.Object
     void finalize()
     Class<?> getClass()
     void notify()
     void notifyAll()
     void wait()
     void wait(long timeout)
     void wait(long timeout, int nanos)

     // Methods inherited from interface java.util.Set
     boolean addAll(Collection<? extends E> c)
     boolean containsAll(Collection<?> c)
     boolean equals(Object o)
     int hashCode()
     boolean removeAll(Collection<?> c)
     boolean retainAll(Collection<?> c)
     Object[] toArray()
     <T> T[] toArray(T[] a)

     // Methods inherited from interface java.util.Collection
     Stream<E> parallelStream()
     boolean removeIf(Predicate<? super E> filter)
     Stream<E> stream()

     // Methods inherited from interface java.lang.Iterable
     void forEach(Consumer<? super T> action)
}

Learn more about methods in the Java documentation:https://docs.oracle.com ...

← Previous topic
class LinkedList<E> in Java

Next topic →
class LinkedHashSet<E> in Java