Question

Code in Java

Create a queue class to store integers and implement following methods:

1) void enqueue(int num): This method will add an integer to the queue (end of the queue).

2) int dequeue(): This method will return the first item in the queue (First In First Out).

3) void display(): This method will display all items in the queue (First item will be displayed first).

4) Boolean isEmpty(): This method will check the queue and if it is empty, this will return true, otherwise false.

Answer 1

class Queue { 
    //front points to front of Queue
    //rear points to rear of Queue
    //size is the length of Queue
    //array is to store the values
    //capacity is the length of the array 
    int front, rear, size; 
    int capacity; 
    int array[]; 
  
    public Queue(int capacity) 
    { 
        this.capacity = capacity; 
        front = this.size = 0; 
        rear = capacity - 1; 
        array = new int[this.capacity]; 
    } 
  
  
    // Queue is empty when size is 0 
    boolean isEmpty(Queue queue) 
    { 
        return (queue.size == 0); 
    } 
  
    //enqueue method to add an num to the queue. 
    //This changes rear and size 
    void enqueue(int num) 
    { 
        //rear=(rear+1)%capacity
        //mod by capacity is to keep rear in range of array length
        this.rear = (this.rear + 1) % this.capacity; 
        
        //Storing the val in array
        this.array[this.rear] = num; 
        
        //Queue is increased by 1
        this.size = this.size + 1; 
    } 
  
    //dequeue method to remove an num from queue. 
    //This changes front and size 
    int dequeue() 
    { 
        //If queue is empty 
        //Case of Underflow
        if (isEmpty(this)) 
            return Integer.MIN_VALUE; 
  
        int num = this.array[this.front];
        
        //front=(front+1)%capacity
        //mod by capacity is to keep fornt in range of array length
        this.front = (this.front + 1) % this.capacity;
        
        //Queue is decreased by 1
        this.size = this.size - 1; 
        return num; 
    } 
    
    void display()
    {
        for(int i=this.front;i < this.front+this.size;i++)
        {
            System.out.print(this.array[i]+" ");
        }
    }
  
} 
  
//Driver class 
public class Test { 
    public static void main(String[] args) 
    { 
        Queue queue = new Queue(100); 
  
        queue.enqueue(100); 
        queue.enqueue(150); 
        queue.enqueue(200); 
        queue.enqueue(400); 
  
        System.out.println("Queue is (before deque) ");
        queue.display();
        System.out.println();
        System.out.println(queue.dequeue()+" dequeued from queue\n"); 
        System.out.println("Queue is (after deque) ");
        queue.display();
        System.out.println();
        System.out.println(queue.dequeue()+" dequeued from queue\n"); 
        System.out.println("Queue is (after deque) ");
        queue.display();
        
        
    } 
} 

Output Screenshot:

(Note: Please refer to the screenshot of the code to understand the indentation of the code.)

Code Screenshots:

Queue and its constructor:

isEmpty() and enqueue():

dequeue() and display():

main():