Java - Adding a time variable to the current time

Question

I am trying to add a given "duration" to the current time. For example,

String runtime = "1h58m"

and I am trying to add this to the current time so that the output looks something like

The runtime of <movie name> is <runtime>. 
<Name> will end at <calculatedDate>

where calculated date is the system current time, plust the given runtime.

This is what I currently have, but don't know how to add the runtime to current system time.

public void playMovie(Movie movie){
        SimpleDateFormat df = new SimpleDateFormat("MM/dd/Y hh:mmaa");
        Date date = new Date();
        System.out.println("The runtime of "+name+" is "+runtime);
        System.out.println(""+name+" will end at "+df.format(date));

Don't use `Date`, but `java.time`, which makes this straightforward. — Louis Wasserman, Sep 11 '21 at 18:56
I recommend you don’t use `SimpleDateFormat` and `Date`. Those classes are poorly designed and long outdated, the former in particular notoriously troublesome. Instead use `ZonedDateTime` and `DateTimeFormatter`, both from [java.time, the modern Java date and time API](https://docs.oracle.com/javase/tutorial/datetime/). — Ole V.V., Sep 12 '21 at 07:52

Arvind Kumar Avinash · Answer 1 · 2021-09-11T20:06:33.073

java.time

The java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern Date-Time API^*.

Solution using java.time, the modern Date-Time API: I recommend you use java.time.Duration which was introduced with Java-8 as part of JSR-310 implementation to model ISO_8601#Duration.

Demo:

import java.time.Duration;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        String runtime = "1h58m";
        runtime = "PT" + runtime;
        Duration duration = Duration.parse(runtime);
        System.out.println(duration);

        LocalDateTime now = LocalDateTime.now();
        LocalDateTime endTime = now.plus(duration);
        System.out.println(endTime);

        // Custom format
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("MM/dd/uuuu hh:mm a", Locale.ENGLISH);
        System.out.println(endTime.format(dtf));
    }
}

Output:

PT1H58M
2021-09-11T23:03:58.749831
09/11/2021 11:03 PM

ONLINE DEMO

Learn more about the modern Date-Time API from Trail: Date Time.

^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.}

2

This is the smart answer. – Ole V.V. Sep 12 '21 at 07:53

score 1 · Answer 2 · answered Sep 11 '21 at 18:57

1

Just use LocalDateTime API (since java 8) like that:

System.out.println("will end at " + LocalDateTime.now().plusHours(1).plusMinutes(30).plusSeconds(45));

answered Sep 11 '21 at 18:57

Dmitrii B

2,672
3
5
14

score 1 · Answer 3 · answered Sep 11 '21 at 19:46

You can use the LocalTime class as shown below.

public void playMovie(Movie movie){

        // Finding Hours, Minutes, and Seconds from the String runtime
        int n = runtime.length();
        int hours = 0;
        int minutes = 0;
        int seconds = 0;
        int i=0;
        for(int j=1; j<n; j++){
            if(runtime.charAt(j)=='h'){
                hours = Integer.parseInt(runtime.substring(i,j));
                i=j+1;
            }
            if(runtime.charAt(j)=='m'){
                minutes = Integer.parseInt(runtime.substring(i,j));
                i=j+1;
            }
            if(runtime.charAt(j)=='s'){
                seconds = Integer.parseInt(runtime.substring(i,j));
                i=j+1;
            }
        }

        //SimpleDateFormat df = new SimpleDateFormat("MM/dd/Y hh:mmaa");
        //Date date = new Date();
        System.out.println("The runtime of "+name+" is "+runtime);
        //System.out.println(""+name+" will end at "+df.format(date));
        
        // Current System Time using the LocalTime class
        LocalTime currentSystemTime = LocalTime.now();  

        // Adding the duration of the movie to the current system time
        LocalTime movieEndTime = currentSystemTime
                .plusHours(hours)
                .plusMinutes(minutes)
                .plusSeconds(seconds);

        System.out.println(""+name+" will end at "+ movieEndTime);
}

Java - Adding a time variable to the current time

3 Answers3

java.time