[Objective]

Array implementation of ring queue

[Idea analysis]

[Code implementation]

import java.util.Scanner;

public class CircleArrayQueueDemo {

	public static void main(String[] args) {
		
		//Test a handful
		System.out.println("Examples of test arrays simulating ring queues~~~");
		
		// Create a circular queue
		CircleArray queue = new CircleArray(4); //Explanation Set 4, the maximum valid data for its queue is 3
		char key = ' '; // Receive user input
		Scanner scanner = new Scanner(System.in);//
		boolean loop = true;
		// Output a menu
		while (loop) {
			System.out.println("s(show): Display queue");
			System.out.println("e(exit): Exit procedure");
			System.out.println("a(add): Add data to queues");
			System.out.println("g(get): Extract data from the queue");
			System.out.println("h(head): View the data of the queue head");
			key = scanner.next().charAt(0);// Receive a character
			switch (key) {
			case 's':
				queue.showQueue();
				break;
			case 'a':
				System.out.println("Output a number");
				int value = scanner.nextInt();
				queue.addQueue(value);
				break;
			case 'g': // Remove data
				try {
					int res = queue.getQueue();
					System.out.printf("The data taken out is%d\n", res);
				} catch (Exception e) {
					// TODO: handle exception
					System.out.println(e.getMessage());
				}
				break;
			case 'h': // View the data of the queue head
				try {
					int res = queue.headQueue();
					System.out.printf("The data of the queue head is%d\n", res);
				} catch (Exception e) {
					// TODO: handle exception
					System.out.println(e.getMessage());
				}
				break;
			case 'e': // Sign out
				scanner.close();
				loop = false;
				break;
			default:
				break;
			}
		}
		System.out.println("Program exit~~");
	}

}


class CircleArray {
	private int maxSize; // Represents the maximum capacity of an array
	//The meaning of the front variable is adjusted: front points to the first element of the queue, that is, arr[front] is the first element of the queue. 
	//The initial value of front = 0
	private int front; 
	//The meaning of the rear variable is adjusted: rear points to the last position of the last element of the queue, because you want to leave a space as a convention.
	//The initial value of rear = 0
	private int rear; // Queue tail
	private int[] arr; // This data is used to store data and simulate queues.
	
	public CircleArray(int arrMaxSize) {
		maxSize = arrMaxSize;
		arr = new int[maxSize];
	}
	
	// Judging whether the queue is full
	public boolean isFull() {
		return (rear  + 1) % maxSize == front;
	}
	
	// Determine whether the queue is empty
	public boolean isEmpty() {
		return rear == front;
	}
	
	// Add data to queues
	public void addQueue(int n) {
		// Judging whether the queue is full
		if (isFull()) {
			System.out.println("The queue is full and data cannot be added~");
			return;
		}
		//Add data directly
		arr[rear] = n;
		//Moving the rear backward, we must consider taking the model here.
		rear = (rear + 1) % maxSize;
	}
	
	// Get the data of the queue and get out of the queue
	public int getQueue() {
		// Determine whether the queue is empty
		if (isEmpty()) {
			// By throwing an exception
			throw new RuntimeException("Queue empty, unable to retrieve data");
		}
		// Here you need to analyze that front is the first element that points to the queue
		// 1. Save the value of front to a temporary variable first
		// 2. Move the front backward and consider taking the model
		// 3. Return temporarily saved variables
		int value = arr[front];
		front = (front + 1) % maxSize;
		return value;

	}
	
	// Display all data for the queue
	public void showQueue() {
		// ergodic
		if (isEmpty()) {
			System.out.println("Queue empty, no data~~");
			return;
		}
		// Thought: How many elements do you traverse from front?
		for (int i = front; i < front + size() ; i++) {
			System.out.printf("arr[%d]=%d\n", i % maxSize, arr[i % maxSize]);
		}
	}
	
	// Find out the number of valid data in the current queue
	public int size() {
		// rear = 2
		// front = 1
		// maxSize = 3 
		return (rear + maxSize - front) % maxSize;   
	}
	
	// Display the header data of the queue, note that it's not fetching the data
	public int headQueue() {
		// judge
		if (isEmpty()) {
			throw new RuntimeException("Queue empty, no data~~");
		}
		return arr[front];
	}
}

[Result Display]