HashSet: Creation and Insertion

HashSet is a class in the java.utils package which implements the Set interface. Some of the features of HashSet are:

1. HashSet does not allow duplicate elements.
2. HashSet allows only one null element.
3. The elements are inserted in random order in a HashSet.
4. A HashSet is internally backed by a HashMap.

Creating a HashSet

There are four different constructors available to create a HashSet in Java:

Using the no-arg constructor

The simplest way to create a HashSet is by using the no-arg constructor. This constructor creates a HashSet with an initial capacity of 16 and a load factor of 0.75.

Below is the code syntax to create a HashSet.

Set<Integer> set= new HashSet<>();

Load factor is a number that defines when a Set should be resized. If the load factor is 0.75, then the Set should be resized when it is 75% full.

Using the Constructor that takes initial capacity

We can also provide the initial capacity while creating the HashSet. If we are already aware that our HashSet will contain more than 16 elements, then it is better to provide some initial capacity as it reduces the number of resizes. In this case, also, the default load factor (0.75) is used.

Using the constructor that takes initial capacity and load factor

We can also provide initial capacity along with the load factor while creating the HashSet. If we don’t want frequent resizing, we can set the load factor to a higher number.

Using the constructor that takes another Set as a parameter

We can also create a HashSet using another Set by passing it to the constructor. The newly created HashSet will have the same size as that of the passed Set, whereas the load factor will default to 0.75.

Inserting an element into a HashSet

There is an add(E e) method available that inserts an element into the HashSet. If the element is not already present, then this method puts the element and returns true. If the element is already present, then it returns false.