How can I add an hour on to the time set but the SimpleDateFormat?

Question

I have a start button with the current time displaying and I want to be able to have a button with a stop time that is an hour later than the current time. How can I go about doing this?

Here is my code for the button displaying the current time

Button stopButton = (Button) this
            .findViewById(R.id.StartTrackingEditStopTime_button);
    // using SimpleDateFormat class
    SimpleDateFormat sdfStopTime = new SimpleDateFormat("hh:mm:ss a",
            Locale.ENGLISH);
    String newStoptime = sdfStopTime
            .format(new Date(System.currentTimeMillis()));

    stopButton.append(newStoptime);

Many thanks for any help or advice on how to do this.

Answer 1

The way you are setting a time with new Date(System.currentTimeMillis()) currently is taking the exact, current millisecond and making a date out of it. If you insist on working with milliseconds, what you need to do is add an hour's worth of milliseconds or 1000 * 60 * 60 = 3600000.

Thus, Way #1 you can fulfill your needs is with this exact code:

Button stopButton = (Button) findViewById(R.id.StartTrackingEditStopTime_button);

SimpleDateFormat sdfStopTime = new SimpleDateFormat("hh:mm:ss a", Locale.ENGLISH);

String newStoptime = sdfStopTime.format(
        new Date(System.currentTimeMillis() + 3600000));

stopButton.setText(newStopTime);

This will work. Way #2 to accomplish this, and useful if you're systematically working with times, is to use the Calendar object. To do this, replace the third line from above with the following code:

Calendar c = Calendar.getInstance();
c.add(Calendar.HOUR, 1);
Date d = c.getTime();
String newStopTime = sdfStopTime.format(d);

Hope this helps! Your choice.

Answer 2

This keeps everything in SimpleDateFormat. No need to create extra objects.

SimpleDateFormat sdfStopTime = new SimpleDateFormat("hh:mm:ss a", Locale.ENGLISH);

System.out.println("Before: " + sdfStopTime.getCalendar().getTime());

sdfStopTime.getCalendar().add(Calendar.HOUR, 1);

System.out.println("After: " + sdfStopTime.getCalendar().getTime());

The first argument of the add() method is the field, hours, minutes etc. The second argument is the amount you want to add, if negative you substract.

Answer 3

Use the Calendar class ( javadoc ). Assuming that you already have a Date now :

Calendar calendar = Calendar.getInstance();
calendar.setTime(now);
calendar.add(Calendar.HOUR, 1);
Date inAnHour = calendar.getTime();

// format inAnHour with your DateFormat and set a button label

Answer 4

You have to add one hour to the current time.

// You don't have to put System.currentTimeMillis() to the constructor.
// Default constructor of Date gives you the current time.
Date stopTime = new Date();
stopTime.setHours(stopTime.getHours() + 1);
String newStoptime = sdfStopTime.format(stopTime);
stopButton.append(newStoptime);

If you don't want to use deprecated functions setHours and getHours , use setTime and getTime and add 3,600,000 milli seconds (1 hour) to the current time:

stopTime.setTime(stopTime.getTime() + 60 * 60 * 1000);

instead of

stopTime.setHours(stopTime.getHours() + 1);