关于Atomic系列与LongAdder的性能差距

public class LongAdderTest {

//    private static AtomicLong counter = new AtomicLong();
    private static LongAdder counter = new LongAdder();
    private static ExecutorService executorService  = Executors.newFixedThreadPool(7);
    public static void main(String[] args) {
        LongAdderTest longAdderTest = new LongAdderTest();
        long l = System.currentTimeMillis();
        //开启N个任务并且每个任务循环M次，最总计数到 sum(N*M) 所花费的时间
        for (int i = 1; i <= 100000; i++) {
            executorService.execute(()->{
               for (int j = 1;j<=5000;j++){
                   longAdderTest.add();
               }
            });
        }
        executorService.shutdown();
        while (true){
            //等待全部线程执行完
            if (executorService.isTerminated()){
                break;
            }
        }
//        System.out.println("result is "+counter.get()+" and  spend time: "+(System.currentTimeMillis()-l)/1000 + "(s)");
        System.out.println("result is "+counter.sum()+" and  spend time: "+(System.currentTimeMillis()-l)/1000 + "(s)");

    }

    private void add(){
//        counter.addAndGet(1);
        counter.add(1L);
    }


}