已经为一些想要练习和学习的人写了一个示例代码。

import java.util.Timer;
import java.util.TimerTask;

public class TimerTest {

    public static void main(String args[]){
        TimerTest.DelayTask task = new DelayTask();
        Timer timer = new Timer();
        /**
         * Use schedule or scheduletAtFixedrate and check the printed result
         */
        timer.schedule(task, 0, 5000);
        //timer.scheduleAtFixedRate(task, 0, 5000);
    }

    public static boolean stop = false;

    public static void delayOneSec(String status){
        try{
            System.out.print(status);
            Thread.sleep(1000);
        }catch(Exception e){
            e.printStackTrace();
        }
    }

    static class DelayTask extends TimerTask{
        int count = 2;

        @Override
        public void run() {
            // TODO Auto-generated method stub
            stop = true;
            for(int i = 0; i < count; i++){
                TimerTest.delayOneSec("T");
            }
            if(count == 2){
                count = 6;
            }else{
                count = 2;
            }
            stop = false;
            new PrintW().start();
        }
    }

    static class PrintW extends Thread{
        @Override
        public void run(){
            while(!stop){
                TimerTest.delayOneSec("W");
            }
        }

    }
}

源代码Timer

public void schedule(TimerTask task, Date firstTime, long period) {
    if (period <= 0)
        throw new IllegalArgumentException("Non-positive period.");
    sched(task, firstTime.getTime(), -period);
}


public void scheduleAtFixedRate(TimerTask task, long delay, long period) {
    if (delay < 0)
        throw new IllegalArgumentException("Negative delay.");
    if (period <= 0)
        throw new IllegalArgumentException("Non-positive period.");
    sched(task, System.currentTimeMillis()+delay, period);
}

下面的代码位于mainloop成TimerThread，，，

currentTime = System.currentTimeMillis();
executionTime = task.nextExecutionTime;
if (taskFired = (executionTime<=currentTime)) {
    if (task.period == 0) { // Non-repeating, remove
        queue.removeMin();
        task.state = TimerTask.EXECUTED;
    } else { // Repeating task, reschedule
        queue.rescheduleMin(
        task.period<0 ? currentTime   - task.period
                      : executionTime + task.period);
           }
    }
}