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This exercise is already available in your IntelliJ as a project. What you need to do is described in the comments at the top of the file in src/main/java/.

package algorithms;
import java.util.Optional;

/**
 * In this exercise, you will implement some methods for a circular linked-list.
 * A circular linked-list is a linked-list for which the last element has a successor: the
 * first element.
 * For example, if the list is 4 -> 5 -> 2, then 4 is the first element, and 2 points towards 4.
 *                             ^         |
 *                             |         |
 *                             -----------
 *
 * We ask you to implement two methods; enqueue and remove which, respectively, add an element at the end of the queue, and
 * removes an element at a given index. The time complexity of each method is note in their specifications.
 */
public class CircularLinkedList {

    public static class Node {
        public int value;
        public Optional<Node> next;

        public Node(int value) {
            this.value = value;
            this.next = Optional.empty();
        }

        public void setNext(Node next) {
            this.next = Optional.of(next);
        }

        public boolean hasNext() {
            return this.next.isPresent();
        }
    }

    public Optional<Node> first;
    public Optional<Node> last;
    public int size;

    public CircularLinkedList() {
        this.first = Optional.empty();
        this.last = Optional.empty();
        this.size = 0;
    }

    public boolean isEmpty() {
        return this.size == 0;
    }

    public Optional<Node> getFirst() {
        return this.first;
    }

    public Optional<Node> getLast() {
        return this.last;
    }

    public void enqueue(int value) {

    }

    public int remove(int index) {
         return -1;
    }
}