Gain insights into Java Collections Framework. Delve into lists, sets, and hashmaps. Learn about data modification, sorting, thread-safety, and internal workings for efficient usage.

Collection is one of the most important topics for Java programming. Without the proper knowledge of every collection type in Java, it becomes difficult for you to decide which option to pick in a particular scenario.

This course will give you a great understanding of all collection types available in the Collections Framework like lists, linked lists, sets, and hashmaps. 

After completing this course, you will know how data can be modified within a collection, how to sort a collection, and how it can be made thread-safe. You will also cover the internal working of each Java collection so you can work with them more efficiently.

Collections in Java

**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**.

```Java
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`.


**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**.

```Java
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`.


Let's discuss HashSet creation and insertion.

Let's Begin

Lists in Java

LinkedList in Java

CopyOnWriteArrayList in Java

Sets in Java

TreeSet in Java

HashMap In Java

TreeMap in Java

LinkedHashMap in Java

Additional Map Implementations

Arrays Class

Collections Class

HashSet: Creation and Insertion

Creating a HashSet