A queue (array based) data structure implementation done in java along with respective time complexities for each method

ArrayQueue.java

/**
  * Queue Data Structure (Array Based Implementation)
  *
  * Enqueue: O(1)
  * Dequeue: O(n)
  * Peek: O(1)
  * Search: O(n)
  */

import java.util.*;

public class ArrayQueue<E> {
  private static final int DEFAULT_CAPACITY = 5;
  private int capacity;
  private int size;
  private Object[] elements;

  public ArrayQueue() throws Exception {
    this(ArrayQueue.DEFAULT_CAPACITY);
  }

  public ArrayQueue(int capacity) throws Exception {
    if (capacity <= 0) {
      throw new Exception("Cannot intialize. Capacity to be greater than zero");
    }
    else {
      this.capacity = capacity;
      this.size = 0;
      this.elements = new Object[capacity];
    }
  }

  /* O(1) */
  public E peek() {
    return (this.isEmpty()) ? null : (E) this.elements[0];
  }

  /* O(1) */
  public void enqueue(E value) {
    if (!Objects.isNull(value) && !this.isFull()) {
      this.elements[this.size++] = value;
    }
  }

  /* O(n) */
  public E dequeue() {
    if (this.isEmpty()) {
      return null;
    }

    E value = (E) this.elements[0];

    for (int i = 0; i < this.size - 1; ++i) {
      this.elements[i] = this.elements[i + 1];
    }

    this.elements[this.size - 1] = null;
    --this.size;
    return value;
  }

  /* O(n) */
  public int search(E value) {
    int index = -1;

    if (!this.isEmpty() && !Objects.isNull(value)) {
      for (int i = 0; i < this.size; ++i) {
        if ((E) this.elements[i] == value) {
          index = i;
          break;
        }
      }
    }

    return index;
  }

  public int size() {
    return this.size;
  }

  public boolean isFull() {
    return this.size == this.capacity;
  }

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

  public String toString() {
    String string = "[";

    for (int i = 0; i < this.size; ++i) {
      string += (i == this.size - 1) ? this.elements[i] : this.elements[i] + ", ";
    }

    return string += "]";
  }

  public static void main(String[] args) throws Exception {
    /* remove this comment and see how this works
    ArrayQueue queue = new ArrayQueue();
    queue.enqueue(12);
    queue.enqueue(123);
    queue.enqueue(4);
    queue.enqueue(11);
    queue.enqueue(23);
    System.out.println("Search: " + queue.search(23));
    System.out.println(queue);
    */
  }
}