throw new IllegalArgumentException("Worker id must be in [0,31]"); 

        } 

        if (!(MIN_DC_ID <= dataCenterId && dataCenterId <= MAX_DC_ID)) { 

            throw new IllegalArgumentException("Data center id must be in [0,31]"); 

        } 

    } 

 

    @Override 

    public synchronized long generate() { 

        long timestamp = System.currentTimeMillis(); 

        // 时钟回拨 

        if (timestamp < lastTimestamp) { 

            throw new IllegalStateException("Clock moved backwards"); 

        } 

        // 同一毫秒内并发 

        if (lastTimestamp == timestamp) { 

            sequence = sequence + 1; 

            if (sequence == MAX_SEQUENCE) { 

                timestamp = untilNextMillis(lastTimestamp); 

                sequence = 0L; 

            } 

        } else { 

            // 下一毫秒重置sequence为0 

            sequence = 0L; 

        } 

        lastTimestamp = timestamp; 

        // 41位时间戳字符串，不够位数左边补"0" 

        String timestampString = leftPadding(Long.toBinaryString(timestamp - epoch), 41); 

        // 5位机器ID字符串，不够位数左边补"0" 

        String workerIdString = leftPadding(Long.toBinaryString(workerId), 5); 

        // 5位数据中心ID字符串，不够位数左边补"0" 

        String dataCenterIdString = leftPadding(Long.toBinaryString(dataCenterId), 5); 

        // 12位序列号字符串，不够位数左边补"0" 

        String seqString = leftPadding(Long.toBinaryString(sequence), 12); 

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