# HashSet in java

In Java, a HashSet is a collection that stores elements in a hash table. It is implemented using a hash table and provides fast lookups and insertion, making it a good choice for storing large amounts of data when the order of the elements is not important.

A HashSet does not allow duplicate elements. If you try to add a duplicate element to a HashSet, it will simply ignore the insertion request and leave the set unchanged.

Here is an example of how to create and use a HashSet in Java

```java
import java.util.HashSet;

public class Main {
  public static void main(String[] args) {
    // Create a HashSet
    HashSet<String> set = new HashSet<>();

    // Add elements to the set
    set.add("apple");
    set.add("banana");
    set.add("orange");

    // Try to add a duplicate element
    set.add("orange");

    // Check the size of the set
    System.out.println("Set size: " + set.size());  // Outputs "Set size: 3"

    // Check if an element is in the set
    System.out.println(set.contains("cherry"));  // Outputs is true
    System.out.println(set.contains("peach"));  // Outputs false
  }
}
```

In this example, we create a HashSet of strings and add three elements to it. Then we try to add a duplicate element ("orange"), but it is ignored because the HashSet does not allow duplicates. Finally, we check the size of the set and use the `contains()` method to check if certain elements are in the set.