This class implements the Set interface, backed by a hash table (actually a HashMap instance). Permits the null element. The class also offers constant time performance for the basic operations like add, remove, contains, and size functions.
- HashSet doesn’t maintain any order, the elements would be returned in any random order.
- Duplicates are not allowed.
- Allows a null value to be present.
- HashSet is non-synchronized, can be synchronized explicitly.
| Constructor | Description |
|---|---|
Set<E> hs = new HashSet<E>(); |
Constructs a new, empty set; the backing HashMap instance has default initial capacity (16) and load factor (0.75) |
Set<E> hs = new HashSet<E>(Collection C); |
Constructs a new set containing the elements in the specified collection. |
Set<E> hs = new HashSet<E>(int initialCapacity); |
Constructs a new, empty set; the backing HashMap instance has the specified initial capacity and default load factor (0.75). |
| Constructor | Description |
|---|---|
| public boolean add(E e) | Adds the specified element to this set if it is not already present. |
| public boolean remove(Object o) | Removes the specified element from this set if it is present. |
| public boolean contains(Object o) | Returns true if this set contains the specified element. |
| public boolean isEmpty() | Returns true if this set contains no elements. |
| public int size() | Returns the number of elements in this set (its cardinality). |