JAVA

Java Queue Array Implementation

class Queue { 
    private static int front, rear, capacity; 
    private static int queue[]; 
   
    Queue(int size) { 
        front = rear = 0; 
        capacity = size; 
        queue = new int[capacity]; 
    } 
   
    // insert an element into the queue
    static void queueEnqueue(int item)  { 
        // check if the queue is full
        if (capacity == rear) { 
            System.out.printf("
Queue is full
"); 
            return; 
        } 
   
        // insert element at the rear 
        else { 
            queue[rear] = item; 
            rear++; 
        } 
        return; 
    } 
   
    //remove an element from the queue
    static void queueDequeue()  { 
        // check if queue is empty 
        if (front == rear) { 
            System.out.printf("
Queue is empty
"); 
            return; 
        } 
   
        // shift elements to the right by one place uptil rear 
        else { 
            for (int i = 0; i < rear - 1; i++) { 
                queue[i] = queue[i + 1]; 
            } 
   
       
      // set queue[rear] to 0
            if (rear < capacity) 
                queue[rear] = 0; 
   
            // decrement rear 
            rear--; 
        } 
        return; 
    } 
   
    // print queue elements 
    static void queueDisplay() 
    { 
        int i; 
        if (front == rear) { 
            System.out.printf("Queue is Empty
"); 
            return; 
        } 
   
        // traverse front to rear and print elements 
        for (i = front; i < rear; i++) { 
            System.out.printf(" %d = ", queue[i]); 
        } 
        return; 
    } 
   
    // print front of queue 
    static void queueFront() 
    { 
        if (front == rear) { 
            System.out.printf("Queue is Empty
"); 
            return; 
        } 
        System.out.printf("
Front Element of the queue: %d", queue[front]); 
        return; 
    } 
} 
 
public class Main {
    public static void main(String[] args) { 
        // Create a queue of capacity 4 
        Queue q = new Queue(4); 
   
        System.out.println("Initial Queue:");
       // print Queue elements 
        q.queueDisplay(); 
   
        // inserting elements in the queue 
        q.queueEnqueue(10); 
        q.queueEnqueue(30); 
        q.queueEnqueue(50); 
        q.queueEnqueue(70); 
   
        // print Queue elements 
        System.out.println("Queue after Enqueue Operation:");
        q.queueDisplay(); 
   
        // print front of the queue 
        q.queueFront(); 
         
        // insert element in the queue 
        q.queueEnqueue(90); 
   
        // print Queue elements 
        q.queueDisplay(); 
   
        q.queueDequeue(); 
        q.queueDequeue(); 
        System.out.printf("
Queue after two dequeue operations:"); 
   
        // print Queue elements 
        q.queueDisplay(); 
   
        // print front of the queue 
        q.queueFront(); 
    } 
}

Java Queue Implementation

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Queue<Integer> q1 = new LinkedList<Integer>();
        //Add elements to the Queue
        q1.add(10);
        q1.add(20);
        q1.add(30);
        q1.add(40);
        q1.add(50);
        System.out.println("Elements in Queue:"+q1);
        //remove () method =>removes first element from the queue
        System.out.println("Element removed from the queue: "+q1.remove());
        //element() => returns head of the queue
        System.out.println("Head of the queue: "+q1.element());
        //poll () => removes and returns the head
        System.out.println("Poll():Returned Head of the queue: "+q1.poll());
        //returns head of the queue
        System.out.println("peek():Head of the queue: "+q1.peek());
        //print the contents of the Queue
        System.out.println("Final Queue:"+q1);
    }
}

implement queue using array in java

// Java program to implement a queue using an array
class Queue {
    private int front, rear, capacity;
    private int queue[];
 
    Queue(int c)
    {
        front = rear = 0;
        capacity = c;
        queue = new int[capacity];
    }
 
    // function to insert an element
    // at the rear of the queue
    static void queueEnqueue(int data)
    {
        // check queue is full or not
        if (capacity == rear) {
            System.out.printf("
Queue is full
");
            return;
        }
 
        // insert element at the rear
        else {
            queue[rear] = data;
            rear++;
        }
        return;
    }
 
    // function to delete an element
    // from the front of the queue
    static void queueDequeue()
    {
        // if queue is empty
        if (front == rear) {
            System.out.printf("
Queue is empty
");
            return;
        }
 
        // shift all the elements from index 2 till rear
        // to the right by one
        else {
            for (int i = 0; i < rear - 1; i++) {
                queue[i] = queue[i + 1];
            }
 
            // store 0 at rear indicating there's no element
            if (rear < capacity)
                queue[rear] = 0;
 
            // decrement rear
            rear--;
        }
        return;
    }
 
    // print queue elements
    static void queueDisplay()
    {
        int i;
        if (front == rear) {
            System.out.printf("
Queue is Empty
");
            return;
        }
 
        // traverse front to rear and print elements
        for (i = front; i < rear; i++) {
            System.out.printf(" %d <-- ", queue[i]);
        }
        return;
    }
 
    // print front of queue
    static void queueFront()
    {
        if (front == rear) {
            System.out.printf("
Queue is Empty
");
            return;
        }
        System.out.printf("
Front Element is: %d", queue[front]);
        return;
    }
}
 
public class StaticQueueinjava {
 
    // Driver code
    public static void main(String[] args)
    {
        // Create a queue of capacity 4
        Queue q = new Queue(4);
 
        // print Queue elements
        q.queueDisplay();
 
        // inserting elements in the queue
        q.queueEnqueue(20);
        q.queueEnqueue(30);
        q.queueEnqueue(40);
        q.queueEnqueue(50);
 
        // print Queue elements
        q.queueDisplay();
 
        // insert element in the queue
        q.queueEnqueue(60);
 
        // print Queue elements
        q.queueDisplay();
 
        q.queueDequeue();
        q.queueDequeue();
        System.out.printf("

after two node deletion

");
 
        // print Queue elements
        q.queueDisplay();
 
        // print front of the queue
        q.queueFront();
    }
}