队列

用数组模拟队列

用两个变量来记录队列的前后

front：随着数据的输出而改变

rear：随着数据的输入而改变

当添加数据时候 指针往后移动 rear + 1 当 front == rear 时队列为空

若指针 rear 小于队列的最大下标则存入，否则无法存入，队列满判断：rear == maxSize - 1

import java.util.Scanner;

public class ArrayQueueDemo {

    public static void main(String[] args) {
        ArrayQueue arrayQueue = new ArrayQueue(3);
        char key = ' ';
        Scanner scanner = new Scanner(System.in);
        boolean loop = true;
        while (loop){
            System.out.println("s 显示队列");
            System.out.println("e 退出程序");
            System.out.println("a 添加数据到队列");
            System.out.println("g 从队列取出数据");
            System.out.println("h 查看队列头数据");
            key = scanner.next().charAt(0);
            switch (key){
                case 's':
                    arrayQueue.showQueue();
                    break;
                case 'e':
                    scanner.close();
                    loop = false;
                    break;
                case 'a':
                    System.out.println("请输入");
                    int value = scanner.nextInt();
                    arrayQueue.addQueue(value);
                    break;
                case 'g':
                    try {
                        int res = arrayQueue.getQueue();
                        System.out.printf("取出数据为%d\n", res);
                    } catch (Exception e){
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'h':
                    try {
                        int res = arrayQueue.headQueue();
                        System.out.printf("队列头数据为%d\n", res);
                    } catch (Exception e){
                        System.out.println(e.getMessage());
                    }
                    break;
            }
            System.out.println("程序退出");
        }
    }

}

class ArrayQueue {
    private int maxSize;
    private int front;
    private int rear;
    private int[] arr;

    public ArrayQueue(int arrMaxSize) {
        maxSize = arrMaxSize;
        arr = new int[maxSize];
        front = -1;
        rear = -1;
    }

    public boolean isFull() {
        return rear == maxSize - 1;
    }

    public boolean isEmpty() {
        return front == rear;
    }

    public void addQueue(int n) {
        if (isFull()) {
            System.out.println("队列已满");
            return;
        }
        arr[++rear] = n;
    }

    public int getQueue() {
        if (isEmpty()) {
            throw new RuntimeException("队列为空");
        }
        return arr[++front];
    }

    public void showQueue() {
        if (isEmpty()) {
            System.out.println("队列为空");
            return;
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.printf("arr[%d]=%d\n", i, arr[i]);
        }
    }

    public int headQueue() {
        if (isEmpty()) {
            throw new RuntimeException("队列为空");
        }
        return arr[front + 1];
    }
}