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public class IdWorker {
 private long workerId; // 这个就是代表了机器id private long datacenterId; // 这个就是代表了机房id private long sequence; // 这个就是代表了一毫秒内生成的多个id的最新序号
 public IdWorker(long workerId, long datacenterId, long sequence) {
 // sanity check for workerId // 这儿不就检查了一下，要求就是你传递进来的机房id和机器id不能超过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;  // 这个是二进制运算，就是5 bit最多只能有31个数字，也就是说机器id最多只能是32以内 private long maxWorkerId = -1L ^ (-1L << workerIdBits);
 // 这个是一个意思，就是5 bit最多只能有31个数字，机房id最多只能是32以内 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(); }
 // 这个是核心方法，通过调用nextId()方法，让当前这台机器上的snowflake算法程序生成一个全局唯一的id public synchronized long nextId() {
 // 这儿就是获取当前时间戳，单位是毫秒 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)); }
  // 下面是说假设在同一个毫秒内，又发送了一个请求生成一个id // 这个时候就得把seqence序号给递增1，最多就是4096 if (lastTimestamp == timestamp) {  // 这个意思是说一个毫秒内最多只能有4096个数字，无论你传递多少进来， //这个位运算保证始终就是在4096这个范围内，避免你自己传递个sequence超过了4096这个范围 sequence = (sequence + 1) & sequenceMask;
 if (sequence == 0) { timestamp = tilNextMillis(lastTimestamp); }  } else { sequence = 0; }
 // 这儿记录一下最近一次生成id的时间戳，单位是毫秒 lastTimestamp = timestamp;
 // 这儿就是最核心的二进制位运算操作，生成一个64bit的id // 先将当前时间戳左移，放到41 bit那儿；将机房id左移放到5 bit那儿；将机器id左移放到5 bit那儿；将序号放最后12 bit // 最后拼接起来成一个64 bit的二进制数字，转换成10进制就是个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(); }
 //---------------测试--------------- 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()); } }}