用java写一个雪花算法

以下是使用Java编写的雪花算法示例代码：

public class SnowflakeAlgorithm {
    private final static long START_STAMP = 1546300800000L;  // 起始时间戳，2019-01-01 00:00:00
    private final static long SEQUENCE_BIT = 12;             // 序列号占用的位数
    private final static long MACHINE_BIT = 5;               // 机器标识占用的位数
    private final static long DATACENTER_BIT = 5;            // 数据中心占用的位数
    
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE_NUM = ~(-1L << SEQUENCE_BIT);
    
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
    
    private long datacenterId;   // 数据中心ID
    private long machineId;      // 机器ID
    private long sequence;       // 序列号
    private long lastTimestamp;  // 上次生成ID的时间戳
    
    public SnowflakeAlgorithm(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
        this.sequence = 0L;
        this.lastTimestamp = -1L;
    }
    
    public synchronized long nextId() {
        long currentTimestamp = System.currentTimeMillis();
        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id");
        }
        
        if (currentTimestamp == lastTimestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE_NUM;
            if (sequence == 0) {
                currentTimestamp = nextTimestamp();
            }
        } else {
            sequence = 0L;
        }
        
        lastTimestamp = currentTimestamp;
        
        return ((currentTimestamp - START_STAMP) << TIMESTAMP_LEFT) | 
               (datacenterId << DATACENTER_LEFT) | 
               (machineId << MACHINE_LEFT) | 
               sequence;
    }
    
    private long nextTimestamp() {
        long currentTimestamp = System.currentTimeMillis();
        while (currentTimestamp <= lastTimestamp) {
            currentTimestamp = System.currentTimeMillis();
        }
        return currentTimestamp;
    }
}

使用示例：

public class SnowflakeAlgorithmTest {
    public static void main(String[] args) {
        SnowflakeAlgorithm snowflake = new SnowflakeAlgorithm(1, 1);
        for (int i = 0; i < 10; i++) {
            long id = snowflake.nextId();
            System.out.println(id);
        }
    }
}