Use of Java timers (Introduction to Timer)

In development, we often need to perform some periodic operations, such as performing an operation every few minutes. At this time we need to set up a timer. The most convenient and efficient way to implement it in Java is to use the java.util.Timer tool class and then schedule the java.util.TimerTask task.

1. Introduction

Timer is a tool that threads use to schedule tasks to be executed in the background thread in the future. Tasks can be scheduled to be executed once or to be repeated periodically. It is actually a thread, TimerTasks owned by scheduled scheduling.

TimerTask is an abstract class, and its subclasses are arranged by Timer to perform tasks once or repeatedly. In fact, it is a class with a run method, and the code that needs to be executed regularly is placed in the run method body.

2. Calling method

Timer timer = Timer(true);

// Note that there is also a Timer class in the javax.swing package. If the swing package is used in the import, pay attention to the name conflict. TTimrtask task = New Timrtask () {

Public void run () {

... // Put the code you need to execute in this.

}

};

//The following are several commonly used methods of scheduling tasks:

timer.schedule(task, time);

//time is a Date type: execute once at a specified time .

timer.schedule(task, firstTime, period);

// firstTime is Date type, period is long

// Starting from firstTime, execute every period milliseconds.

timer.schedule(task, delay)

// delay is long type: executed once after delay milliseconds from now

timer.schedule(task, delay, period)

// delay is long , period is long: after delay milliseconds from now, it will be executed every period

// milliseconds.

What is the difference between schedule() and scheduleAtFixedRate()?

First of all, schedule(TimerTask task,Date time) and schedule(TimerTask task,long delay) are only single execution operations, and there is no situation of calling the task multiple times, so there is no way to call the scheduleAtFixedRate method. They all implement the same functions, so what's the difference?

(1) The schedule() method pays more attention to maintaining the stability of the interval: ensuring that it can be called once every period.

(2) The scheduleAtFixedRate() method pays more attention to maintaining the stability of the execution frequency: ensuring that the frequency of multiple calls approaches the period time. If the time of a certain call is greater than the period, the next time it will be less than the period as much as possible to ensure that the frequency is close to the period. period.

3. Example demonstration

Customized task:

import java.util.Timer;

import java.util.TimerTask;

public void run () {

// TODO Auto-generated method stub

System.out.println("Execute task...");

}

}

Call java.util.Timer:

import java. util.Timer;

/**

* Arrange the specified task to perform repeated fixed-rate period execution starting at the specified time firstTime

* Execute once every day at 12 noon

*/

public class Test {

public static void main(String[] args){

Timer timer = new Timer();

Calendar calendar = Calendar.getInstance();

calendar.set(Calendar.HOUR_OF_DAY, 12);//Control the hour

calendar.set(Calendar.MINUTE, 0);//Control the minute

calendar.set(Calendar.SECOND, 0);//Control seconds

Date time = calendar.getTime();//The execution time of the task is 12:00:00

       

Timer timer = new Timer();

// 12:00 every day Execute the operation, delay it for one day and then execute it again

timer.schedule(new TimerTaskTest(), time, 1000 * 60 * 60 * 24); The timer tool class Timer, please point out if there are any deficiencies. Those who are interested can check out another timer open source project: QUARTZ. Sharing is a kind of happiness, persistence is a kind of spirit.

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