面試官問訂單ID是如何生成的?難道不是MySQL自增主鍵

import java.util.UUID;

/**
 * @author yideng
 * @apiNote UUID範例
 */
public class UUIDTest {
    public static void main(String[] args) {
        String orderId = UUID.randomUUID().toString().replace("-", "");
        System.out.println(orderId);
    }
}

/**
 * @author 一燈架構
 * @apiNote 雪花演演算法
 **/
public class SnowFlake {

    /**
     * 起始時間戳，從2021-12-01開始生成
     */
    private final static long START_STAMP = 1638288000000L;

    /**
     * 序列號佔用的位數 12
     */
    private final static long SEQUENCE_BIT = 12;

    /**
     * 機器標識佔用的位數
     */
    private final static long MACHINE_BIT = 10;

    /**
     * 機器數量最大值
     */
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);

    /**
     * 序列號最大值
     */
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long TIMESTAMP_LEFT = SEQUENCE_BIT + MACHINE_BIT;

    /**
     * 機器標識
     */
    private long machineId;
    /**
     * 序列號
     */
    private long sequence = 0L;
    /**
     * 上一次時間戳
     */
    private long lastStamp = -1L;

    /**
     * 構造方法
     * @param machineId 機器ID
     */
    public SnowFlake(long machineId) {
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new RuntimeException("機器超過最大數量");
        }
        this.machineId = machineId;
    }

    /**
     * 產生下一個ID
     */
    public synchronized long nextId() {
        long currStamp = getNewStamp();
        if (currStamp < lastStamp) {
            throw new RuntimeException("時鐘後移，拒絕生成ID！");
        }

        if (currStamp == lastStamp) {
            // 相同毫秒內，序列號自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            // 同一毫秒的序列數已經達到最大
            if (sequence == 0L) {
                currStamp = getNextMill();
            }
        } else {
            // 不同毫秒內，序列號置為0
            sequence = 0L;
        }

        lastStamp = currStamp;

        return (currStamp - START_STAMP) << TIMESTAMP_LEFT // 時間戳部分
                | machineId << MACHINE_LEFT             // 機器標識部分
                | sequence;                             // 序列號部分
    }

    private long getNextMill() {
        long mill = getNewStamp();
        while (mill <= lastStamp) {
            mill = getNewStamp();
        }
        return mill;
    }

    private long getNewStamp() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        // 訂單ID生成測試，機器ID指定第0臺
        SnowFlake snowFlake = new SnowFlake(0);
        System.out.println(snowFlake.nextId());
    }
}