Help with this one would be greatly appreciated. Please write the code in an organized manner. Thank you for your help!

Queue of distinct strings Abstract Concept of a queue of distinct strings: A queue of distinct strings, p, is a collection of strings with a front and end where a string cannot exist more than once in the collection. For example, the collection of strings ("ab, cd", "ae", "bd) is a queue with front = "ab and end = "hd". The only operations supported are addition of a string at the end known as enqueue, and deletion of a string from the front known as dequeue. Implementation of a queue of distinct strings: The following class, QueueOfDistinctStrings, represents a queue of distinct strings. import java.util.ArrayList; public class QueueOfDistinctStrings { // Overview: QueueOfDistinct Strings are mutable, bounded // collection of distinct strings that operate in // FIFO (First-In-First-Out) order. // The abstraction function is: // a) Write the abstraction function here // // // The rep invariant is: // b) Write the rep invariant here /// //the rep private ArrayList items; // constructor public QueueOfDistinctStrings () { // EFFECTS: Creates a new QueueOfDistinctStrings object items = new ArrayList(); } // MODIFIES: this // EFFECTS: Appends the element at the end of the queue if the element is not in the queue, otherwise // does nothing. public void enqueue (String element) throws Exception { if(element == null) throw new Exception(); if(false == items. contains (element)) items.add (element); } public String dequeue () throws Exception { // MODIFIES: this // EFFECTS: Removes an element from the front of the queue if (items.size() == 0) throw new Exception(); return items.remove(0); } public boolean repok () { // EFFECTS: Returns true if the rep invariant holds for this // object; otherwise returns false // c) Write the code for the repoK() here public String toString() { // EFFECTS: Returns a string that contains the strings in the queue, the front element and the end element. // Implements the abstraction function. 11 d) Write the code for the toString() here }