Write a Java Program to implement a queue using an array.
What is Queue in Java?
Queue is a particular kind of abstract data type or collection in which the entities in the collection are kept in order and the principal (or only) operations on the collection are the addition of entities to the rear terminal position and removal of entities from the front terminal position. This makes queue a First-In-First-Out (FIFO) data structure.
How to declare Queue?
In Java, you can declare a queue using the Queue interface, which is a part of the Java Collections Framework. Since Queue is an interface, you will need to instantiate a concrete class that implements it.
To declare a queue of integers using an array in Java, you can use the ArrayDeque class, which is a resizable-array implementation of the Deque interface, which itself extends the Queue interface. Here’s an example:
Queue<Integer> myQueue = new ArrayDeque<Integer>();
Queue Class Methods in Java
Some of the common methods provided by the Queue interface include:
- add(E element): Adds the specified element to the end of the queue.
- offer(E element): Inserts the specified element into the queue if it is possible to do so without violating capacity restrictions. Returns true upon success and false if the queue is full.
- remove(): Removes the element at the front of the queue and returns it. Throws a NoSuchElementException if the queue is empty.
- poll(): Retrieves and removes the head of the queue, or returns null if the queue is empty.
- element(): Retrieves the element at the front of the queue without removing it. Throws a NoSuchElementException if the queue is empty.
- peek(): Retrieves the element at the front of the queue without removing it, or returns null if the queue is empty.
Here is the source code of the Java Program to implement a queue using array. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.
/* * Queue Implementation in Java */ import java.util.*; /* Class arrayQueue */ class arrayQueue { protected int Queue[] ; protected int front, rear, size, len; /* Constructor */ public arrayQueue(int n) { size = n; len = 0; Queue = new int[size]; front = -1; rear = -1; } /* Function to check if queue is empty */ public boolean isEmpty() { return front == -1; } /* Function to check if queue is full */ public boolean isFull() { return front==0 && rear == size -1 ; } /* Function to get the size of the queue */ public int getSize() { return len ; } /* Function to check the front element of the queue */ public int peek() { if (isEmpty()) throw new NoSuchElementException("Underflow Exception"); return Queue[front]; } /* Function to insert an element to the queue */ public void insert(int i) { if (rear == -1) { front = 0; rear = 0; Queue[rear] = i; } else if (rear + 1 >= size) throw new IndexOutOfBoundsException("Overflow Exception"); else if ( rear + 1 < size) Queue[++rear] = i; len++ ; } /* Function to remove front element from the queue */ public int remove() { if (isEmpty()) throw new NoSuchElementException("Underflow Exception"); else { len-- ; int ele = Queue[front]; if ( front == rear) { front = -1; rear = -1; } else front++; return ele; } } /* Function to display the status of the queue */ public void display() { System.out.print("\nQueue = "); if (len == 0) { System.out.print("Empty\n"); return ; } for (int i = front; i <= rear; i++) System.out.print(Queue[i]+" "); System.out.println(); } } /* Class QueueImplement */ public class QueueImplement { public static void main(String[] args) { Scanner scan = new Scanner(System.in); System.out.println("Array Queue Test\n"); System.out.println("Enter Size of Integer Queue "); int n = scan.nextInt(); /* creating object of class arrayQueue */ arrayQueue q = new arrayQueue(n); /* Perform Queue Operations */ char ch; do{ System.out.println("\nQueue Operations"); System.out.println("1. insert"); System.out.println("2. remove"); System.out.println("3. peek"); System.out.println("4. check empty"); System.out.println("5. check full"); System.out.println("6. size"); int choice = scan.nextInt(); switch (choice) { case 1 : System.out.println("Enter integer element to insert"); try { q.insert( scan.nextInt() ); } catch(Exception e) { System.out.println("Error : " +e.getMessage()); } break; case 2 : try { System.out.println("Removed Element = "+q.remove()); } catch(Exception e) { System.out.println("Error : " +e.getMessage()); } break; case 3 : try { System.out.println("Peek Element = "+q.peek()); } catch(Exception e) { System.out.println("Error : "+e.getMessage()); } break; case 4 : System.out.println("Empty status = "+q.isEmpty()); break; case 5 : System.out.println("Full status = "+q.isFull()); break; case 6 : System.out.println("Size = "+ q.getSize()); break; default : System.out.println("Wrong Entry \n "); break; } /* display Queue */ q.display(); System.out.println("\nDo you want to continue (Type y or n) \n"); ch = scan.next().charAt(0); } while (ch == 'Y'|| ch == 'y'); } }
1. A class called arrayQueue is defined which contains the following instance variables:
- Queue: An integer array to store the elements of the queue.
- front: An integer variable to store the index of the front element.
- rear: An integer variable to store the index of the rear element.
- size: An integer variable to store the maximum size of the queue.
- len: An integer variable to store the current number of elements in the queue.
2. The constructor of the arrayQueue class initializes all instance variables to their default values.
3. The isEmpty() method checks if the queue is empty by checking if front is equal to -1.
4. The isFull() method checks if the queue is full by checking if front is equal to 0 and rear is equal to size – 1.
5. The getSize() method returns the current number of elements in the queue.
6. The peek() method returns the front element of the queue without removing it. It throws an exception if the queue is empty.
7. The insert(int i) method inserts an element into the queue. It throws an exception if the queue is full.
8. The remove() method removes and returns the front element of the queue. It throws an exception if the queue is empty.
9. The display() method displays the elements of the queue.
10. A class called QueueImplement is defined which contains the main method.
11. The main method creates an object of the arrayQueue class and performs various queue operations using a menu-driven approach.
Array Queue Test Enter Size of Integer Queue 5 Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 4 Empty status = true Queue = Empty Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 1 Enter integer element to insert 24 Queue = 24 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 1 Enter integer element to insert 6 Queue = 24 6 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 1 Enter integer element to insert 16 Queue = 24 6 16 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 1 Enter integer element to insert 19 Queue = 24 6 16 19 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 1 Enter integer element to insert 32 Queue = 24 6 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 1 Enter integer element to insert 14 Error : Overflow Exception Queue = 24 6 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 5 Full status = true Queue = 24 6 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 3 Peek Element = 24 Queue = 24 6 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 2 Removed Element = 24 Queue = 6 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 2 Removed Element = 6 Queue = 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 6 Size = 3 Queue = 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 3 Peek Element = 16 Queue = 16 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 2 Removed Element = 16 Queue = 19 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 2 Removed Element = 19 Queue = 32 Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 2 Removed Element = 32 Queue = Empty Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 2 Error : Underflow Exception Queue = Empty Do you want to continue (Type y or n) y Queue Operations 1. insert 2. remove 3. peek 4. check empty 5. check full 6. size 4 Empty status = true Queue = Empty Do you want to continue (Type y or n) n
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