AtomicInteger類如何在Java項(xiàng)目中使用

public class Sample1 {
  private static Integer count = 0;
  synchronized public static void increment() {
    count++;
  }
}

public class Sample2 {
  private static AtomicInteger count = new AtomicInteger(0);
  public static void increment() {
    count.getAndIncrement();
  }
}

public class AtomicInteger extends Number implements java.io.Serializable {
  private static final long serialVersionUID = 6214790243416807050L;
  // setup to use Unsafe.compareAndSwapInt for updates
  private static final Unsafe unsafe = Unsafe.getUnsafe();
  private static final long valueOffset;
  static {
    try {
      valueOffset = unsafe.objectFieldOffset
        (AtomicInteger.class.getDeclaredField("value"));
    } catch (Exception ex) { throw new Error(ex); }
  }
  private volatile int value;

 public class AtomicTest {
  static long randomTime() {
    return (long) (Math.random() * 1000);
  }
  public static void main(String[] args) {
    // 阻塞隊(duì)列，能容納100個(gè)文件
    final BlockingQueue<File> queue = new LinkedBlockingQueue<File>(100);
    // 線程池
    final ExecutorService exec = Executors.newFixedThreadPool(5);
    final File root = new File("D:\\ISO");
    // 完成標(biāo)志
    final File exitFile = new File("");
    // 原子整型，讀個(gè)數(shù)
    // AtomicInteger可以在并發(fā)情況下達(dá)到原子化更新，避免使用了synchronized，而且性能非常高。
    final AtomicInteger rc = new AtomicInteger();
    // 原子整型，寫個(gè)數(shù)
    final AtomicInteger wc = new AtomicInteger();
    // 讀線程
    Runnable read = new Runnable() {
      public void run() {
        scanFile(root);
        scanFile(exitFile);
      }
      public void scanFile(File file) {
        if (file.isDirectory()) {
          File[] files = file.listFiles(new FileFilter() {
            public boolean accept(File pathname) {
              return pathname.isDirectory() || pathname.getPath().endsWith(".iso");
            }
          });
          for (File one : files)
            scanFile(one);
        } else {
          try {
            // 原子整型的incrementAndGet方法，以原子方式將當(dāng)前值加 1，返回更新的值
            int index = rc.incrementAndGet();
            System.out.println("Read0: " + index + " " + file.getPath());
            // 添加到阻塞隊(duì)列中
            queue.put(file);
          } catch (InterruptedException e) {
          }
        }
      }
    };
    // submit方法提交一個(gè) Runnable 任務(wù)用于執(zhí)行，并返回一個(gè)表示該任務(wù)的 Future。
    exec.submit(read);
    // 四個(gè)寫線程
    for (int index = 0; index < 4; index++) {
      // write thread
      final int num = index;
      Runnable write = new Runnable() {
        String threadName = "Write" + num;
        public void run() {
          while (true) {
            try {
              Thread.sleep(randomTime());
              // 原子整型的incrementAndGet方法，以原子方式將當(dāng)前值加 1，返回更新的值
              int index = wc.incrementAndGet();
              // 獲取并移除此隊(duì)列的頭部，在元素變得可用之前一直等待（如果有必要）。
              File file = queue.take();
              // 隊(duì)列已經(jīng)無對象
              if (file == exitFile) {
                // 再次添加"標(biāo)志"，以讓其他線程正常退出
                queue.put(exitFile);
                break;
              }
              System.out.println(threadName + ": " + index + " " + file.getPath());
            } catch (InterruptedException e) {
            }
          }
        }
      };
      exec.submit(write);
    }
    exec.shutdown();
  }
}