public class IdWorker {
    private long workerId;
    private long datacenterId;
    private long sequence;
    public IdWorker(long workerId, long datacenterId, long sequence) {
        // sanity check for workerId
        // 這兒不就檢查了一下，要求就是你傳遞進(jìn)來的機(jī)房id和機(jī)器id不能超過32，不能小于0
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(
                    String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(
                    String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        System.out.printf(
                "worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d",
                timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId);
        this.workerId = workerId;
        this.datacenterId = datacenterId;
        this.sequence = sequence;
    }
    private long twepoch = 1288834974657L;
    private long workerIdBits = 5L;
    private long datacenterIdBits = 5L;
    // 這個是二進(jìn)制運算，就是 5 bit最多只能有31個數(shù)字，也就是說機(jī)器id最多只能是32以內(nèi)
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
    // 這個是一個意思，就是 5 bit最多只能有31個數(shù)字，機(jī)房id最多只能是32以內(nèi)
    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private long sequenceBits = 12L;
    private long workerIdShift = sequenceBits;
    private long datacenterIdShift = sequenceBits + workerIdBits;
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << sequenceBits);
    private long lastTimestamp = -1L;
    public long getWorkerId() {
        return workerId;
    }
    public long getDatacenterId() {
        return datacenterId;
    }
    public long getTimestamp() {
        return System.currentTimeMillis();
    }
    public synchronized long nextId() {
        // 這兒就是獲取當(dāng)前時間戳，單位是毫秒
        long timestamp = timeGen();
        if (timestamp < lastTimestamp) {
            System.err.printf("clock is moving backwards.  Rejecting requests until %d.", lastTimestamp);
            throw new RuntimeException(String.format(
                    "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        if (lastTimestamp == timestamp) {
            // 這個意思是說一個毫秒內(nèi)最多只能有4096個數(shù)字
            // 無論你傳遞多少進(jìn)來，這個位運算保證始終就是在4096這個范圍內(nèi)，避免你自己傳遞個sequence超過了4096這個范圍
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0;
        }
        // 這兒記錄一下最近一次生成id的時間戳，單位是毫秒
        lastTimestamp = timestamp;
        // 這兒就是將時間戳左移，放到 41 bit那兒；
        // 將機(jī)房 id左移放到 5 bit那兒；
        // 將機(jī)器id左移放到5 bit那兒；將序號放最后12 bit；
        // 最后拼接起來成一個 64 bit的二進(jìn)制數(shù)字，轉(zhuǎn)換成 10 進(jìn)制就是個 long 型
        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift) | sequence;
    }
    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }
    private long timeGen() {
        return System.currentTimeMillis();
    }
    // ---------------測試---------------
    public static void main(String[] args) {
        IdWorker worker = new IdWorker(1, 1, 1);
        for (int i = 0; i < 30; i++) {
            System.out.println(worker.nextId());
        }
    }
}