Java计时器错误

Question

我的Java类中有这段代码

package me.mario.timer;

import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;

public class AutoSyncDatabase {
    Runnable helloRunnable = new Runnable() {
        public void run() {
         System.out.println("Hello world");
        }
    };
    ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
    executor.scheduleAtFixedRate(helloRunnable, 0, 3, TimeUnit.SECONDS);
}

但是我在此行收到错误Syntax error on tokens, delete these tokens：

executor.scheduleAtFixedRate(helloRunnable, 0, 3, TimeUnit.SECONDS);

我尝试了很多方法来修复它，但是没有任何运气。

任何帮助将不胜感激！

谢谢。