转载：https://blog.csdn.net/wenzhi20102321/article/details/78681379

ScheduledThreadPoolExecutor ，Timer和TimerTask的比较

误差说明：

我在后台程序看看一下Timer执行程序是有可能延迟1、2毫秒，如果是1秒执行一次的任务，1分钟有可能延迟60毫秒，一小时延迟3600毫秒，相当于3秒，实际用户看不出什么区别。
但是，如果我的程序需要每40毫秒就执行一次任务，如果还是有1、2毫秒的误差，1秒钟就有25毫秒的误差，大概40秒就有1秒的误差，十几分钟就有十几秒的误差，这对UI显示来说是延迟非常严重的了。
而我用ScheduledThreadPoolExecutor来做40毫秒的间隔任务，一般十几分钟才有1秒多的误差，这个还是能接受的。
这也是我用ScheduledThreadPoolExecutor这个类的原因。

ScheduledThreadPoolExecutor的介绍

ScheduledThreadPoolExecutor，它可另行安排在给定的延迟后运行命令，或者定期执行命令。需要多个辅助线程时，或者要求 ThreadPoolExecutor 具有额外的灵活性或功能时，此类要优于Timer。

使用Timer和TimerTask存在一些缺陷：

1.Timer只创建了一个线程。当你的任务执行的时间超过设置的延时时间将会产生一些问题。

2.Timer创建的线程没有处理异常，因此一旦抛出非受检异常，该线程会立即终止。

JDK 5.0以后推荐使用ScheduledThreadPoolExecutor。该类属于Executor Framework，它除了能处理异常外，还可以创建多个线程解决上面的问题

Timer和TimerTask的使用

这个大家应该都是会使用的了，但是还是給给大家看看代码：

        Timer  timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                log.e("time:");

            }
        }, 2000, 40);//2000表示第一次执行任务延迟时间，40表示以后每隔多长时间执行一次run里面的任务

ScheduledThreadPoolExecutor的使用

这里先学会简单使用再深入探讨。

        ScheduledThreadPoolExecutor  scheduled = new ScheduledThreadPoolExecutor(2);
        scheduled.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                loge("time:");
            }
        }, 0, 40, TimeUnit.MILLISECONDS);//0表示首次执行任务的延迟时间，40表示每次执行任务的间隔时间，TimeUnit.MILLISECONDS执行的时间间隔数值单位

间隔单位毫秒：TimeUnit.MILLISECONDS
间隔单位秒：TimeUnit.SECONDS
间隔单位分钟：TimeUnit.MINUTES
间隔单位小时：TimeUnit.HOURS
间隔单位天：TimeUnit.DAYS

定时器的一个实例

使用Timer和TimerTask、ScheduledThreadPoolExecutor显示秒的定时器

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效果：

这里看起来是每秒刷新一次UI，但是我为了看40毫秒的延迟效果，是每40 毫秒index加一，添加25次后，刷新一次UI，表面上看起来是和每秒刷新的效果。

代码：

package com.example.wenzhi.scheduledthreadpoolexecutordemo;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class MainActivity extends AppCompatActivity {

    TextView tv_time;
    int      time;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv_time = (TextView) findViewById(R.id.tv_time);

    }

    Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (time % 25 == 0) {
                tv_time.setText("" + time / 25);
            }
        }
    };

    /**
     * 普通定时器
     */
    Timer timer;

    public void timer(View view) {
        stopTimer1();
        timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                loge("time:" + time++);//add
                handler.sendEmptyMessage(11);
            }
        }, 2000, 40);
    }

    public void stop(View view) {
        stopTimer1();
    }

    /**
     * 停止定时器
     */
    private void stopTimer1() {
        if (timer != null) {
            timer.cancel();
            timer = null;
        }
    }


    /**
     * 稳定的定时器
     */
    ScheduledThreadPoolExecutor scheduled;

    public void timer2(View view) {
        stopTimer2();
        scheduled = new ScheduledThreadPoolExecutor(2);
        scheduled.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                loge("time:" + time++);
                handler.sendEmptyMessage(11);
            }
        }, 0, 40, TimeUnit.MILLISECONDS);

    }

    public void stop2(View view) {
        stopTimer2();
    }

    /**
     * 停止定时器
     */
    private void stopTimer2() {
        if (scheduled != null) {
            scheduled.shutdownNow();
            scheduled = null;
        }
    }

    private void loge(String msg) {
        Log.e("TAG", msg);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        System.exit(0);
    }

    /**
     * 数据清零
     */
    public void clear(View view) {
        time = 0;
        tv_time.setText("" + time);
    }

}

Log数据对比

Timer定时器

11-29 01:08:09.940 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:0
11-29 01:08:09.980 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:1
11-29 01:08:10.020 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:2
11-29 01:08:10.060 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:3
11-29 01:08:10.100 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:4
11-29 01:08:10.140 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:5
11-29 01:08:10.180 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:6
11-29 01:08:10.224 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:7
11-29 01:08:10.264 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:8
11-29 01:08:10.304 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:9
11-29 01:08:10.344 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:10
11-29 01:08:10.384 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:11
11-29 01:08:10.424 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:12
11-29 01:08:10.468 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:13
11-29 01:08:10.508 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:14
11-29 01:08:10.548 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:15
11-29 01:08:10.592 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:16
11-29 01:08:10.632 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:17
11-29 01:08:10.672 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:18
11-29 01:08:10.712 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:19
11-29 01:08:10.752 6070-20203/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:20

可以看到上面时间间隔不是很稳定，有几个是间隔40多毫秒的

ScheduledThreadPoolExecutor定时器

11-29 01:11:13.492 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:0
11-29 01:11:13.528 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:1
11-29 01:11:13.564 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:2
11-29 01:11:13.604 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:3
11-29 01:11:13.644 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:4
11-29 01:11:13.684 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:5
11-29 01:11:13.724 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:6
11-29 01:11:13.764 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:7
11-29 01:11:13.804 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:8
11-29 01:11:13.844 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:9
11-29 01:11:13.888 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:10
11-29 01:11:13.924 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:11
11-29 01:11:13.984 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:12
11-29 01:11:14.004 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:13
11-29 01:11:14.044 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:14
11-29 01:11:14.084 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:15
11-29 01:11:14.124 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:16
11-29 01:11:14.164 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:17
11-29 01:11:14.204 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:18
11-29 01:11:14.244 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:19
11-29 01:11:14.284 6070-22987/com.example.wenzhi.scheduledthreadpoolexecutordemo E/TAG: time:20

可以看到上面的数据除了第一个和第二个，其他的数据都是非常稳定的，间隔时间都是40毫秒。

而且时间越长越能看出，这两种定时器的差距。

ScheduledThreadPoolExecutor定时任务