public class IdWorker {   private long workerId; // 這個就是代表了機器id   private long datacenterId; // 這個就是代表了機房id   private long sequence; // 這個就是代表了一毫秒內(nèi)生成的多個id的最新序號   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)來的機房id和機器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));       }       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();   }   // 這個是核心方法，通過調(diào)用nextId()方法，讓當(dāng)前這臺機器上的snowflake算法程序生成一個全局唯一的id   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));       }              // 下面是說假設(shè)在同一個毫秒內(nèi)，又發(fā)送了一個請求生成一個id       // 這個時候就得把seqence序號給遞增1，最多就是4096       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;       // 這兒就是最核心的二進(jìn)制位運算操作，生成一個64bit的id       // 先將當(dāng)前時間戳左移，放到41 bit那兒；將機房id左移放到5 bit那兒；將機器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());       }   }}