# Java - Timer
###### tags: `Java` `Basic Java`

Java Timer有兩種
1. Timer
2. ScheduledExecutorService

## Timer示範：

public class TimerDemo {
    public static void main(String[] args) {
        // 1. create timer object
        Timer timer = new Timer();
        // 2. use it on task
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName() + " executing...");
            }
        }, 3000, 2000);
    }
}

**BUT!!!!!!!!!**

Timer是single thread，在使用上會產生許多不便，故還是比較建議使用第二種方式建立定時任務

## ScheduledExecutorService
這個API是基於thread pool開發的，在開發中會比較常使用

public class ScheduledExecutorDemo {
    public static void main(String[] args) {
        // 1. create a scheduled thread pool
        ScheduledExecutorService pool = Executors.newScheduledThreadPool(3);

        // 2. create scheduled task
        pool.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName() + " executing...");
            }
        }, 0, 2, TimeUnit.SECONDS);
    }
}