How to add current time to a previous date in java?

Question

I was trying to add current time into previous date. But it was adding in current date with time not with previous date.

see my bellow code:

Date startUserDate = ;//this is my previous date object;
startUserDate.setTime(new Date().getTime());// here i'm trying to add current time in previous date.
System.out.println("current time with previous Date :"+startUserDate);

In previous date there is no time and i want to add current time in previous date.I can do this, please help me out.

Answer 1

Use calendar object

Get instance of calendar object and set your past time to it Date startUserDate = ;

    Calendar calendar = Calendar.getInstance();
    calendar.settime(startUserDate);

Create new calendar instance

     Calendar cal = Calendar.getInstance();
     cal.settime(new Date());

format the date to get string representation of time of current date

        SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
        String currentdate =  sdf.format(cal.getTime());

split that string to get hour minute and second object

                String hh = expiry.split(":")[0];
                String mm = expiry.split(":")[1];
                String ss = expiry.split(":")[2];

add it to the previous calendar object

    calendar .add(Calendar.HOUR_OF_DAY, hh);
    calendar .add(Calendar.MINUTE, mm);
    calendar .add(Calendar.SECOND, ss);

this date will have current time added to your date

   Date newDate = calendar.getTime;

Answer 2

Use Calendar:

• first set the date/time of the first calendar object to the old date

• object use as second Calendar object to set the current time on the

• first calendar object then convert it back to date

as follow:

//E.g. for startUserDate 
Date startUserDate = new Date(System.currentTimeMillis() - (24L * 60L * 60L * 1000L) - (60L * 60L * 1000L));//minus 1 day and 1 hour
Calendar calDateThen = Calendar.getInstance();
Calendar calTimeNow = Calendar.getInstance();
calDateThen.setTime(startUserDate);
calDateThen.set(Calendar.HOUR_OF_DAY, calTimeNow.get(Calendar.HOUR_OF_DAY));
calDateThen.set(Calendar.MINUTE, calTimeNow.get(Calendar.MINUTE));
calDateThen.set(Calendar.SECOND, calTimeNow.get(Calendar.SECOND));
startUserDate = calDateThen.getTime();
System.out.println(startUserDate);

The second Calendar object calTimeNow can be replaced with Calendar.getInstance() where it is used.

Answer 3

You can do it using DateFormat and String, here's the solution that you need:

Code:

DateFormat df = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
String timeString = df.format(new Date()).substring(10); // 10 is the beginIndex of time here

DateFormat df2 = new SimpleDateFormat("MM/dd/yyyy");
String startUserDateString = df2.format(startUserDate);

startUserDateString = startUserDateString+" "+timeString;
// you will get this format "MM/dd/yyyy HH:mm:ss" 

//then parse the new date here
startUserDate = df.parse(startUserDateString);

Explanation:

Just convert the current date to a string and then extract the time from it using .substring() method, then convert your userDate to a string concatenate the taken time String to it and finally parse this date to get what you need.

Example:

You can see it working in this ideone DEMO.

Which takes 02/20/2002 in input and returns 02/20/2002 04:36:14 as result.