Java用数组实现队列（非环状）

import java.util.Scanner;

public class Start {
    public static void main(String[] args) {
        boolean loop = true;
        Queue queue = new Queue(4);
        while (loop) {
            System.out.println("a(append):入队");
            System.out.println("r(remove):出队");
            System.out.println("h(head):查看队列头部情况");
            System.out.println("e(exit):退出程序");
            Scanner scanner = new Scanner(System.in);
            char key = scanner.next().charAt(0);
            switch (key) {
                case 'a':
                    System.out.println("输入想要入队的元素值");
                    int num = scanner.nextInt();
                    try {
                        queue.addQueue(num);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'r':
                    try {
                        int number = queue.removeQueue();   // 与 case: 'b' 中 num 不能名字相同，考虑局部变量的作用域问题
                        System.out.println("出队元素为：" + number);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'h':
                    try {
                        queue.headQueue();
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'e' :
                    scanner.close();
                    loop = false;
                    break;
                default:
                    System.out.println("请输入正确序号");
                    break;
            }
        }

    }
}




 class Queue {
    
    int front = -1;
    int rear = -1;
    private int[] arr;
    private int arrSize;

    public Queue(int arrSize) {
        this.arrSize = arrSize;
        arr = new int[arrSize];
    }

    public Queue() {
    }

    public void setArr(int arrSize) {
        this.arrSize = arrSize;
        arr = new int[arrSize];
    }

    // 队列是否为满
    public boolean isFull() {
        return rear == arrSize - 1;
    }

    // 队列是否为空
    public boolean isEmpty() {
        return rear == front;
    }

    // 元素加队列
    // 注意: 1. 判断队列是否为满 2. 未满则加入新元素
    public void addQueue(int num) {
        if (this.isFull()) {
            throw new RuntimeException("队列已满，无法继续进队列");
        }
        rear++;
        arr[rear] = num;
    }

    // 元素出队列
    // 注意： 1. 出队列前判断队列是否为空 2. 未空则输出移除元素
    public int removeQueue() {
        if (this.isEmpty()) {
            throw new RuntimeException("队列为空，无法继续出队列");
        }
        front++;
        return arr[front];
    }

    public void headQueue() {
        if(this.isEmpty()) {
            throw new RuntimeException("队列为空");
        }
        System.out.println("arr的头部数据为：" + arr[front + 1]);
    }
}