public class TestA { static int a=0;  public static void main(String[] args) {
       
        ExecutorService executorService = Executors.newFixedThreadPool(10);  for (int i = 0; i < 20; i++) {
            executorService.execute(()->{ synchronized ("锁"){ for (int j = 0; j < 10000; j++) { a++;  }
                }
            });   } try {
            Thread.sleep(2000);  System.out.println(a);  } catch (InterruptedException e) {
            e.printStackTrace();  }
    }
}