How to add 10 minutes to my (String) time?

Java 7 Time API

    DateTimeFormatter df = DateTimeFormatter.ofPattern("HH:mm");

    LocalTime lt = LocalTime.parse("14:10");
    System.out.println(df.format(lt.plusMinutes(10)));

Use Calendar.add(int field,int amount) method.

I would use Joda Time, parse the time as a LocalTime, and then use

time = time.plusMinutes(10);

Short but complete program to demonstrate this:

import org.joda.time.*;
import org.joda.time.format.*;

public class Test {
    public static void main(String[] args) {
        DateTimeFormatter formatter = DateTimeFormat.forPattern("HH:mm");
        LocalTime time = formatter.parseLocalTime("14:10");
        time = time.plusMinutes(10);
        System.out.println(formatter.print(time));
    }       
}

Note that I would definitely use Joda Time instead of java.util.Date/Calendar if you possibly can - it's a much nicer API.

Something like this

 String myTime = "14:10";
 SimpleDateFormat df = new SimpleDateFormat("HH:mm");
 Date d = df.parse(myTime); 
 Calendar cal = Calendar.getInstance();
 cal.setTime(d);
 cal.add(Calendar.MINUTE, 10);
 String newTime = df.format(cal.getTime());

As a fair warning there might be some problems if daylight savings time is involved in this 10 minute period.