How to Implement Queue in Java using Array and Generics?

// Java Program to Implement Queue using Array and Generics // Importing input output classes import java.io.*; // Importing all utility classes import java.util.*; // Class 1 // Helper Class(user defined - generic queue class) class queue<T> {  // front and rear variables are initially initiated to  // -1 pointing to no element that control queue  int front = -1, rear = -1;  // Creating an object of ArrayList class of T type  ArrayList<T> A = new ArrayList<>();  // Method 1  // Returns value of element at front  T front()  {  // If it is not pointing to any element in queue  if (front == -1)  return null;  // else return the front element  return A.get(front);  }  // Method 2  // Returns value of element at rear  T rear()  {  // If it is not pointing to any element in queue  if (rear == -1)  return null;  return A.get(rear);  }  // Method 3  // Inserts element at the front of queue  void enqueue(T X)  {  // If queue is empty  if (this.empty()) {  front = 0;  rear = 0;  A.add(X);  }  // If queue is not empty  else {  front++;  if (A.size() > front) {  // Mov front pointer to next  A.set(front, X);  }  else  // Add element to the queue  A.add(X);  }  }  // Method 4  // Deletes elements from the rear from queue  void dequeue()  {  // if queue doesn't have any elements  if (this.empty())  // Display message when queue is already empty  System.out.println("Queue is already empty");  // If queue has only one element  else if (front == rear) {  // Both are pointing to same element  front = rear = -1;  }  // If queue has more than one element  else {  // Increment the rear  rear++;  }  }  // Method 5  // Checks whether the queue is empty  boolean empty()  {  // Both are initialized to same value  // as assigned at declaration means no queue made  if (front == -1 && rear == -1)  return true;  return false;  }  // Method 6  // Print the queue  // @Override  public String toString()  {  if (this.empty())  return "";  String Ans = "";  for (int i = rear; i < front; i++) {  Ans += String.valueOf(A.get(i)) + "->";  }  Ans += String.valueOf(A.get(front));  return Ans;  } } // Class 2 // Main class class GFG {  // Main driver method  public static void main(String args[])  {  // Case 1 : Integer Queue  // Creating object of queue Class (user defined)  // Declaring object of integer type  queue<Integer> q1 = new queue<>();  // Pushing elements to the integer object created  // Custom input integer entries  q1.enqueue(5);  q1.enqueue(10);  q1.enqueue(20);  // Print the queue after inserting integer elements  System.out.println(  "q1 after enqueue of 3 elements:\n" + q1);  q1.dequeue();  System.out.println("q1 after dequeue :\n" + q1);  // Case 2 : String Queue  // Creating object of queue Class (user defined)  // Declaring object of string type  queue<String> q2 = new queue<>();  // Pushing elements to the String object created  // Custom input string entries  q2.enqueue("hello");  q2.enqueue("world");  q2.enqueue("GFG");  // Print the queue after inserting string elements  System.out.println(  "\nq2 after enqueue of 3 elements:\n" + q2);  // Printing front and rear of the above queue  System.out.println("q2 front = " + q2.front()  + ", q2 rear = " + q2.rear());  // Case 3 : Float Queue  // Creating object of queue Class (user defined)  // Declaring object of float type  queue<Float> q3 = new queue<>();  // Display message only  System.out.println(  "\nCreated new Float type queue q3...");  // Display whether queue is empty or not  // using the empty() method  System.out.println(  "Checking if queue is empty or not :\n"  + q3.empty());  } }