JAVA

java queue

import java.util.*;

Queue<Integer> queue = new LinkedList<Integer>();
// use non-primative types when constructing

// to add a value to the back of queue:
queue.add(7);

// to remove and return front value:
int next = queue.remove();

// to just return front value without removing:
int peek = queue.peek();

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(); 
    } 
}

queue in java

queues, //add, remove, peek , size()
    Queue<Integer> q = new LinkedList<>();
	- Unlike stacks, a queue is open at both its ends. (one end enqueue & one end remove data, dequeue) FIFO
	- enqueue() − add (store) an item to the queue. 
	- dequeue() − remove (access) an item from the queue.
	- peek() − Gets the element at the front of the queue without removing it.
	- isfull() − Checks if the queue is full.
	- isempty() − Checks if the queue is empty.
      
      Queue<Integer> queue = new LinkedList<Integer>();
        queue.add(10);
        queue.add(20);
        int a = queue.remove();
        int peek = queue.peek();
        System.out.println(queue + " " + a); //[20] 10

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);
    }
}

Java How to use Queue?

// LinkedList implementation of Queue
Queue<String> animal1 = new LinkedList<>();

// Array implementation of Queue
Queue<String> animal2 = new ArrayDeque<>();

// Priority Queue implementation of Queue
Queue<String> animal 3 = new PriorityQueue<>();

Java Queue

The Queue interface is available in java.util package and extends the Collection interface. The queue collection is used to hold the elements about to be processed and provides various operations like the insertion, removal etc. It is an ordered list of objects with its use limited to insert elements at the end of the list and deleting elements from the start of list i.e. it follows the FIFO or the First-In-First-Out principle.

LinkedList, ArrayBlockingQueue and PriorityQueue are the most frequently used implementations.   

queue in java

//this a basic one 
public class prosses {
    int [] s;
    int quu;
    int tu;
  
    prosses () {//constructor
        s = new int[20];
        quu = -1;
        tu = 0;
    }
  
    void enqueue (int d) {//for input and prosses
        if (quu >= 19) {
            System.out.println("stack is full");
        } else {
            s[++quu] = d;

        }
    }
  
    int dequeue(){//to send the output
        if(quu<0 && quu>19 && tu<0 && tu>19) {
            System.out.println("not possible");
            return 'n';
        }

        return s[tu++];
    }
}