Java定时器Timer与TimerTask的使用详解

public class Timer {
    //默认给线程命名："Timer-" + serialNumber()
	public Timer() {
        this("Timer-" + serialNumber());
    }
    //指定Timer的名字
    public Timer(String name) {
        thread.setName(name);
        thread.start();
    }
    //isDaemon：是否为守护线程
    public Timer(boolean isDaemon) {
        this("Timer-" + serialNumber(), isDaemon);
    }
    //给定线程名字，守护线程与否
    public Timer(String name, boolean isDaemon) {
        thread.setName(name);
        //setDaemon是指定线程是否为守护线程，true是守护线程，当主线程退出，      守护线程退出
        thread.setDaemon(isDaemon);
        thread.start();
    }    
}
//TimerThread类 继承Thread
class TimerThread extends Thread{
	private void mainLoop() {
	......
	//每次执行下标为1的TimerTask
	task = queue.getMin();
	......
	}
}
//TaskQueue 类
class TaskQueue {
	//TaskQueue 中存储TimerTask
    private TimerTask[] queue = new TimerTask[128];
    //返回数组中下标1的TimerTask
    TimerTask getMin() {
        return queue[1];
    }
}

public class TimerDemo {
	//指定Timer为守护线程，run方法结束Timer线程会结束。
    private static Timer timer = new Timer(true);
    //TimerTask 具体的定时任务
    static public class MyTask extends TimerTask {
        @Override
        public void run() {
            System.out.println("已运行，时间为：" + new Date());
        }
    }
    public static void main(String[] args) {
    	//创建定时任务
        MyTask myTask = new MyTask();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        //早于当前时间，定时任务会立即执行
        String dateString = "2020-06-01 09:56:00";
        try {
            Date taskDate = sdf.parse(dateString);
            //启动定时任务
            timer.schedule(myTask,taskDate);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class TimerDemo {
    private static Timer timer = new Timer();
    static public class MyTaskA extends TimerTask {
        @Override
        public void run() {
        	//只输出一次，MyTaskA 任务将会移除
            System.out.println("MyTaskA已运行，时间为：" + new Date());
            //执行TimerTask的cancel方法，将自身任务从队列中移除
            this.cancel();
        }
    }
    static public class MyTaskB extends TimerTask {
        @Override
        public void run() {
        	//移除MyTaskA任务，MyTaskB 任务不受影响
            System.out.println("MyTaskB已运行，时间为：" + new Date());
        }
    }
    public static void main(String[] args) {
        MyTaskA myTaskA = new MyTaskA();
        MyTaskB myTaskB = new MyTaskB();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateString = "2020-07-01 15:19:00";
        try {
            Date taskDate = sdf.parse(dateString);
            timer.schedule(myTaskA,taskDate,2000);
            timer.schedule(myTaskB,taskDate,2000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class TimerDemo {
    private static Timer timer = new Timer();
    static public class MyTaskA extends TimerTask {
        @Override
        public void run() {
            System.out.println("MyTaskA已运行，时间为：" + new Date());
            //执行Timer类的cancel方法，将Timer中所有任务从队列中移除
            timer.cancel();
        }
    }
    static public class MyTaskB extends TimerTask {
        @Override
        public void run() {
            //MyTaskB也会被移除，因为MyTaskA与MyTaskB是队列执行，先执行MyTaskA再执行MyTaskB
            //MyTaskA中走了timer.cancel()，所以MyTaskB不会执行
            System.out.println("MyTaskB已运行，时间为：" + new Date());
        }
    }
    public static void main(String[] args) {
        MyTaskA myTaskA = new MyTaskA();
        MyTaskB myTaskB = new MyTaskB();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateString = "2020-07-01 15:19:00";
        try {
            Date taskDate = sdf.parse(dateString);
            timer.schedule(myTaskA,taskDate,2000);
            timer.schedule(myTaskB,taskDate,2000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public void cancel() {
        synchronized(queue) {
            thread.newTasksMayBeScheduled = false;
            queue.clear();
            queue.notify();  // In case queue was already empty.
        }
    }

public class TimerDemo {
    private static Timer timer = new Timer();
    static public class MyTaskA extends TimerTask {
        @Override
        public void run() {
            System.out.println("MyTaskA已运行，时间为：" + new Date());
            try {
                //任务执行时间是1s
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("MyTaskA已结束，时间为：" + new Date());
        }
    }
    public static void main(String[] args) {
        MyTaskA myTaskA = new MyTaskA();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateString = "2020-07-02 14:31:00";
        try {
            Date taskDate = sdf.parse(dateString);
            //3s执行一次任务
            timer.scheduleAtFixedRate(myTaskA,taskDate,3000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}