/*** 生成序列號，最大值為MAX_VAL。如果達到MAX_VAL，從0開始。*/ public class SerialGenerator {public static final int MAX_VAL = 999;public static final int R_NUM = getRNum(MAX_VAL);private static AtomicReference<AtomicInteger> ref = new AtomicReference<AtomicInteger>(new AtomicInteger(0));public static int getSerialNo() {AtomicInteger old = ref.get();int serialNo = old.getAndIncrement();while (serialNo > MAX_VAL) {AtomicInteger update = new AtomicInteger(0);ref.compareAndSet(old, update);old = ref.get();serialNo = old.getAndIncrement();}return serialNo;}/*** 求整數有幾位，如234是3位。* @param i* @return*/private static final int getRNum(int i) {if (i < 0) {throw new RuntimeException("Illegal arg i, i=" + i);}int div = i;int num = 1;div /= 10;while (div > 0) {div /= 10;num++;}return num;}/*** 獲取序列號，該序列號為字符串表示，長度固定為序列號的最大長度，* 如果長度不足，則在前面補0，比如"015"* @return*/public static String getSerialNoInStr() {int serialNo = getSerialNo();int rnum = getRNum(serialNo);StringBuilder sb = new StringBuilder();for (int i=0; i<R_NUM-rnum; i++) {sb.append("0");}return sb.append(serialNo).toString();}@Testpublic static void main(String[] args) throws InterruptedException, ExecutionException {//測10次for (int t=0; t<10; t++) {int taskNum = 1 + new Random().nextInt(19);@SuppressWarnings("unchecked")Future<Integer>[] fs = new Future[taskNum]; // System.err.println(taskNum);ExecutorService executor = Executors.newFixedThreadPool(taskNum);for (int i=0; i<taskNum; i++) {fs[i] = executor.submit(new Callable<Integer>() {int sum = 0;@Overridepublic Integer call() throws Exception {for (int i=0; i<=MAX_VAL; i++) {sum += getSerialNo();}return new Integer(sum);} });}int result = 0;for (Future<Integer> future : fs) {result += future.get();}int expect = 0;for (int i=0; i<taskNum; i++) {for (int j=0; j<=MAX_VAL; j++) {expect += j;}}Assert.assertEquals(expect, result);System.out.println(taskNum + " : " + expect);}Random random = new Random();for (int i=0; i<10000; i++) {getSerialNoInStr();if (random.nextInt(1000) < 9) {System.out.println(getSerialNoInStr());} } }}

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