Getting the system time in action listener

Question

I have a class that implements Actionlistener. Upon clicking the button from this class I want it do something at a precise time I specified, earlier, and elsewhere. So I have made these classes :

class DoSomething implements ActionListener{
     public void actionPerformed(ActionEvent a){
     while(true){
         String test = obtainTime.time;

    if(test.matches("(.*)17:29:30(.*)")){
         Class.doSomethingMethod();
    }
        //Rest of the code
     }
     }
}

class ObtainTime{
     static DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
     static Calendar cal = Calendar.getInstance();
     static String time = dateFormat.format(cal.getTime());
}

So the problem is, I only get the time from when I clicked it. The second thing is the button becomes unclickable since it is still running, is there a way to make it clickable again while the code still runs in the background? Thank you for any help.

Answer 1

If you're doing something quick and/or something that requires you to update a UI when you reach the target time, you want to use a Java Swing Timer. More documentation on this is here: Oracle's Swing Timer tutorial. If you're doing a long-running task, you'll want to follow andersoj's suggestion and use a scheduled executor.

Answer 2

If you want to do several things paralely, you'd have to use threads.. You can do this by extending your class with Thread or implementing Runnable interface Nice tutorial for both ways can be found here.

To get the time & date in formate, that will match your pattern, check this document, where you can find patterns for foramtting date & time in java.

Answer 3

Your first question: While it's confusing, I think you are asking why you only get the time as measured by the first time you push the button. The answer is because when you push the button for the first time, you load the ObtainTime class. When you load that class, once and only once, the static initializers run. The line:

static String time = dateFormat.format(cal.getTime());

Is a static initializer. What you probably mean to do is something more like this:

class DoSomething implements ActionListener{

  private final ScheduledExecutor scheduler = executors.newSingleThreadScheduledExecutor();
  private final long timeToRunAction;

   DoSomething(long timeToRunAction) {
     this.timeToRunAction = timeToRunAction;
   }

   public void actionPerformed(ActionEvent a)
   {
     long currentTime = System.currentTimeMillis();
     long delayTime = timeToRunAction - currentTime;
     scheduler.schedule(new Runnable() {
         public void run() { Class.doSomethingMethod(); }
     }, delayTime, TimeUnit.MILLISECONDS);
   }
}

If you use this class, then when you instantiate it you specify the target time in the constructor. You might want this to be more dynamic, that's fine, you just make the timeToRunAction field mutable and provide a way to set it. Times here are specified in milliseconds from the unix epoch. If you need to do some calendar magic to figure out your target time, I have left that out.

Your second question: Instead of rolling your own concurrency, I strongly recommend using ScheduledExecutor.schedule() to do this. You will need to use the calendar to compute the correct delay time, probably in milliseconds, to schedule the activity.

Answer 4

Looks like you are using Swing as your GUI API. you should use javax.swing.SwingWorker to achieve what you are looking for. It can be done as follows:

import javax.swing.*;
import java.util.*;
import java.text.*;
import java.awt.*;

public class SWorker extends JFrame
{
    JLabel label ;
    DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
    Calendar cal = Calendar.getInstance();
    static SwingWorker worker;
    public void createAndShowGUI()
    {
        setTitle("SwingWorker Demo");
        label = new JLabel();
        getContentPane().add(label,BorderLayout.NORTH);
        setSize(300,200);
        worker = new SwingWorker<String, String>() 
        {
            @Override
            public String doInBackground() 
            {
               cal = Calendar.getInstance();
               String test = dateFormat.format(cal.getTime());
               while (!(test.matches("(.*)23:41:30(.*)")) && ! isCancelled())
               {
                   publish(new String[] {test});
                    Thread.sleep(5);//Added to sleep the thread for 5 ms so that load could be shed from processor..
                   cal = Calendar.getInstance();
                   test = dateFormat.format(cal.getTime());
               }
               return test;
            }

            @Override
            public void done() //This method is called when doInBackground() finishes. i.e when pattern is matched
            {
                try
                {
                    //Call here the method that you want to call after the time matches.
                    label.setText(get() + " Time's up ...!!");  
                }
                catch (Exception ex){}

            }
            @Override
            public void process(java.util.List<String> chunks)
            {
                label.setText(chunks.get(chunks.size()-1));
            }
        };
        String time = dateFormat.format(cal.getTime());
        label.setText(time);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }
    public void start()
    {
        worker.execute();
    }
    public static void main(String st[])
    {
        SwingUtilities.invokeLater( new Runnable()
        {
            @Override
            public void run()
            {
                SWorker sWorker = new SWorker();
                sWorker.createAndShowGUI();
                sWorker.start();
            }
        });
    }
}

To know more about how to use SwingWorker look at this official tutorial on SwingWorker