Simple Clock in Java with JFrame

Question

I've been messing around with NetBeans creating a clock that is always on top and always loads in the bottom right of the screen. I've gotten it completed however I think my code is eating away at memory, after I left it over night I came back to 1.4GB of memory being used and a large amount of the CPU being used. I'm new to Java programming so I'm hoping this isn't normal!

In my main thread I create a new Calendar object each run. Moving this out of the Thread creates a Calendar object that is initialised with the current time but never updates, is there a better method of doing this?

I'm not used to dealing with Threads and I think I may have gotten turned around. Can anyone suggest improvements to the following that will lower my memory footprint and cpu usage?

public JavaClockGUI() {
    initComponents();    

    new Thread()
    {
        public void run()
        {
            while(true) 
            {
                Calendar cal = new GregorianCalendar();
                int hour = cal.get(Calendar.HOUR_OF_DAY);
                int min = cal.get(Calendar.MINUTE);
                int sec = cal.get(Calendar.SECOND);

                String time = String.format("%02d",hour) + ":" + String.format("%02d",min) + ":" + String.format("%02d",sec);

                lblTime.setText(time);
            }
        }
    }.start();
}

Answer 1

try declaring the variables outside the while loop and having a delay to lessen execution of the loop on a given amount of time.

public void run()
    {
        Calendar cal;
        int hour;
        int min;
        int sec;
        String time;
        while(true) 
        {
            cal = new GregorianCalendar();
            hour = cal.get(Calendar.HOUR_OF_DAY);
            min = cal.get(Calendar.MINUTE);
            sec = cal.get(Calendar.SECOND);

            String time = String.format("%02d",hour) + ":" +  String.format("%02d",min) + ":" + String.format("%02d",sec);

            lblTime.setText(time);
            //delay the loop for 1 sec
            try {
                Thread.currentThread().sleep(1000);
                System.out.println(x);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
        }
    }

Answer 2

Hope this will help you.

Date(){
    DateFormat dateFormat = new SimpleDateFormat("MMM dd, yyyy HH:mm:ss)";
    Date date = new Date();
    boolean condition = false;

    while(!false){
      lbltime.setText(dateFormat.format(date));
      Thread.sleep(1000);
   }
}

Answer 3

Two important things about performance:

• Not to create a new object inside the loop every iteration (and avoid heap allocation as much as possible)
• Execute the task periodically (and not let a while(true) loop run rampant).

I don't know what's the best way to do it, but I have a short, simple and accurate one:

Use a Timer to execute a TimerTask at a fixed rate. The method scheduleAtFixedRate will execute the task (run method) at a fixed rate with respect to absolute time, and not with respect to previous execution. That is, if one of the executions is delayed, the next one will commence regardless of the delay (they will be shorter apart). Calling Thread.sleep(1000) will not behave this way and will result in accumulating delays in the long run.

For receiving the time and formatting it, the Java8 Date-Time API (java.time) is the way to go.

public class Example {

    public static void main(String[] args) {

        DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM);
        new Timer().scheduleAtFixedRate(new TimerTask() {

            @Override
            public void run() {

                System.out.println(LocalTime.now().format(formatter));
            }
        }, 0, 1000);
    }
}

Notes:

• You can make your class extend TimerTaks if you don't like the anonymous construction here, or create an inner class.
• Explore DateTimeFormatter to find the format you want if this one is not what you're looking for.

• You can hold a reference to timer,

  Timer timer = new Timer();
  timer.scheduleAtFixedRate(...);
  

  If you need it later.