java volatile关键字使用方法及注意事项

public class VolatileData {

  //声明为volatile类型
  private volatile int counter = 0;

  /**
  * 返回counter变量的值
  * @return
  */
  public int getCounter() {
    return counter;
  }

  /**
  * 自增counter变量的值
  */
  public void increaseCounter() {
    ++counter;
  }
}

public class VolatileThread extends Thread {
  private final VolatileData volatileData;

  public VolatileThread(VolatileData volatileData) {
    this.volatileData = volatileData;
  }

  /**
  * 调用VolatileData类中的两个方法，进行取值和自增操作
  */
  @Override
  public void run() {
    int oldValue = volatileData.getCounter();
    System.out.println("[Thread " + Thread.currentThread().getId() + "]: Old value = " + oldValue);
    volatileData.increaseCounter();
    int newValue = volatileData.getCounter();
    System.out.println("[Thread " + Thread.currentThread().getId() + "]: New value = " + newValue);
  }
 }

public class VolatileMain {

  private final static int TOTAL_THREADS = 2;

  public static void main(String[] args) throws InterruptedException {
    VolatileData volatileData = new VolatileData();

    Thread[] threads = new Thread[TOTAL_THREADS];
    for(int i = 0; i < TOTAL_THREADS; ++i)
      threads[i] = new VolatileThread(volatileData);

    //开始读取变量值的操作
    for(int i = 0; i < TOTAL_THREADS; ++i)
      threads[i].start();

    //等待所有线程操作终止
    for(int i = 0; i < TOTAL_THREADS; ++i)
      threads[i].join();
  }
}

[Thread 10]: Old value = 0
[Thread 11]: Old value = 0
[Thread 10]: New value = 1
[Thread 11]: New value = 2