public class SmallSnowflake { public static final int NODE_SHIFT = 10; public static final int SEQ_SHIFT = 12; public static final short MAX_NODE = 1023; public static final short MAX_SEQUENCE = 4095; private short sequence; private long referenceTime; private int node; public SmallSnowflake(int node) { if (node < 0 || node > MAX_NODE) { throw new IllegalArgumentException(String.format("node must be between %s and %s", 0, MAX_NODE)); } this.node = node; } public synchronized long next() { long currentTime = this.getCurrentTimeMillis(); long counter; if (currentTime < referenceTime) { throw new RuntimeException(String.format("Last referenceTime %s is after reference time %s", referenceTime, currentTime)); } else if (currentTime > referenceTime) { this.sequence = 0; } else { if (this.sequence < SmallSnowflake.MAX_SEQUENCE) { this.sequence++; } else { throw new RuntimeException("Sequence exhausted at " + this.sequence); } } counter = this.sequence; referenceTime = currentTime; return currentTime << NODE_SHIFT << SEQ_SHIFT | node << SEQ_SHIFT | counter; } protected long getCurrentTimeMillis() { return System.currentTimeMillis() / 1000; }public class LargeSnowflake extends SmallSnowflake { public LargeSnowflake(int node) { super(node); } @Override protected long getCurrentTimeMillis() { return System.currentTimeMillis(); }} public static void main(String[] args) { LargeSnowflake lsf = new LargeSnowflake(1); System.out.println(lsf.next()); SmallSnowflake ssf = new SmallSnowflake(1); System.out.println(ssf.next()); }