public class FieldVisibility {

  volatile int a = 1;
  volatile int b = 2;

//  static final Set<ExecutionResult> results = new HashSet<>();

  /**
   * 四种结果：
   * ExecutionResult{a=3, b=2} write1 -> read -> write2
   * ExecutionResult{a=3, b=3} write1 -> write2 -> read
   * ExecutionResult{a=1, b=2} read -> write1 -> write2
   * ExecutionResult{a=1, b=3} 发生可见性问题
   *
   * 解决可见性问题可以使用volatile关键字，修饰之后运行结果：
   *
   * @param args
   * @throws InterruptedException
   */
  public static void main(String[] args) throws InterruptedException {

    for(int i=0;i<50000;i++) {
      FieldVisibility fieldVisibility = new FieldVisibility();

      Thread thread1 = new Thread(() -> {
        try {
          Thread.sleep(1);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        fieldVisibility.change();
      });

      Thread thread2 = new Thread(() -> {
        try {
          Thread.sleep(1);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        fieldVisibility.print();
      });

      thread1.start();
      thread2.start();
//      thread1.join();
//      thread2.join();
    }
//    for(ExecutionResult result : results) {
//      System.out.println(result.toString());
//    }
  }

  public void change() {
    a = 3;
    b = a;
  }

  public void print() {
//    results.add(new ExecutionResult(a, b));
    System.out.println("a=" + a + "; b=" + b);
  }
}

救命，老师，同学们！