HashSet

 import java.util.HashSet;

// HashSet is an interface in java.

// if we want to remove  an element which is not exist in set then we do not get any error.

// in set there is no concept of index , so we use for each loop.

// if any element is already present , then we can not add again , no error.

public class Basic{

    public static void main(String[] args) {

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

        // Insert O(1)

        set.add(89);

        set.add(10);

        set.add(-987);

        set.add(100);

        // size O(1)

        System.out.println(set.size());

        //in set elements are stroe randomly

        System.out.println(set);

        // remove element O(1)

        set.remove(10);

        System.out.println(set);

        // search - true/false O(1)

        System.out.println(set.contains(89));

        // convert set into array

        Object[] arr = set.toArray();

        for(Object ele : arr){

            System.out.print(ele+" ");

        }

        // acess elements of set

        for(int ele : set){

            System.out.print(ele+" ");

        }

        // for remove all elements from set

        set.clear();

        System.out.println(set);

    }

}