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math with dates , + - and ADD

Hello guys i have a tricky question for you that i really cant find a solution out there.
What i want to do is to have 3 date/time inputs on simpledateformat
Date 1
Date 2
Date 3
and basicaly i want to get difference of months days hours and minutes from date 1 - date2 and result of those 2 dates to be added on the firth date
for example 11/3/2017 12:30 - 7/3/2017 = 4 days and ADD that to current date 13/3/2017 13:30 + 4 days and 1 hour = 17/3/2017 14:30
i know how to get the diference in days hours and minutes , i cant get the second part of adding the result to the current date
any ideas?
thank you in dvance

Use Calendar class to add days and hours
Calendar cal = Calendar.getInstance();
cal.setTime(yourDate);
cal.add(Calendar.DAY_OF_MONTH, yourDays); //adds days to your date
cal.add(Calendar.HOUR_OF_DAY, yourHours); //adds hours to your date
cal.getTime(); //to get Date instance
To decrement dates just add negative number, for example:
int yourDays = -daysVariable;
int yourHours = -hoursVariable; //
Calendar cal = Calendar.getInstance();
cal.setTime(yourDate);
cal.add(Calendar.DAY_OF_MONTH, yourDays); //decrement days
cal.add(Calendar.HOUR_OF_DAY, yourHours); //decrement hours
cal.getTime(); //to get Date instance

Get a date object using the simpledate format
Because it is an object of the same type
Comparison is possible

I think you need to use getTime and add days throught miliseconds.
For example, if you can get the difference of days you should use something like this
date1.getTime() + 24*60*60*1000*4
(where 4 is the difference you want to add)
You can use Calendar too.

Thank you all for your ultra fast replies!
I solved it by using Mij Solution
Calendar cal = Calendar.getInstance();
cal.setTime(yourDate);
cal.add(Calendar.DAY_OF_MONTH, yourDays); //adds days to your date
cal.add(Calendar.HOUR_OF_DAY, yourHours); //adds hours to your date
cal.getTime(); //to get Date instance
To add days and
tis code to decrese days
Calendar cal = Calendar.getInstance();
cal.setTime(yourDate);
cal.add(Calendar.DAY_OF_MONTH, -yourDays); //adds days to your date
cal.add(Calendar.HOUR_OF_DAY, -yourHours); //adds hours to your date
cal.getTime(); //to get Date instance
and to control if date is bigget than my current date i used this condition
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
Date strDate = sdf.parse(valid_until);
if (new Date().after(strDate)) {
catalog_outdated = 1;
}
it returns -1 if the date is past from current
+1 if date is bigger that current or whatever
and 0 if dates are equal
again thank you!

Android , Calendar.getInstance() not giving the correct month

I am trying to write code to find the Day difference between tow date but Calendar.getInstance() keep getting the date for previous month instead of current month
for example :Current 17/7/2014 it get 17/6/2014
my code :
TextView textview=(TextView) findViewById (R.id.textView1);
Calendar cal = Calendar.getInstance();
Calendar startDate=Calendar.getInstance();
startDate.set(Calendar.DAY_OF_MONTH, 1);
startDate.set(Calendar.MONTH,1);
startDate.set(Calendar.YEAR, 2013);
long diff=(((cal.getTimeInMillis()-startDate.getTimeInMillis())/(1000*60*60*24))+1);
String sdiff=String.valueOf(diff);
String stt=cal.get(Calendar.YEAR) +"_"+cal.get(Calendar.MONTH)+"_"+cal.get(Calendar.DAY_OF_MONTH);
textview.setText(stt);

Months start at 0, not at 1, but you really don't have to worry about this if you don't use magic numbers when getting or setting month but instead use the constants. So not this:
startDate.set(Calendar.MONTH,1); // this is February!
but rather
startDate.set(Calendar.MONTH, Calendar.JANUARY);

Months in Java's Calendar start with 0 for January, so July is 6, not 7.
Calendar.MONTH javadocs:
The first month of the year in the Gregorian and Julian calendars is JANUARY which is 0
Add 1 to the result of get.
(cal.get(Calendar.MONTH) + 1)
This also affects your set call. You can either subtract 1 when passing a month number going in, or you can use a Calendar constant, e.g. Calendar.JANUARY.
You can also use a SimpleDateFormat to convert it to your specific format, without having to worry about this quirk.
SimpleDateFormat sdf = new SimpleDateFormat("yyyy_MM_dd");
String stt = sdf.format(cal.getTime());

how to get the timestamp of previous dates in java? [duplicate]

This question already has answers here:
How to subtract n days from current date in java? [duplicate]
(5 answers)
Closed 9 years ago.
In my shopping cart application, I am storing all the purchase dates in timestamp.
Suppose, I want to get the timestamp of purchase date n days before (n is configurable). How will I get it using java?
example: something like
purchasedateBefore5days = currentTimestamp_in_days - 5;
I am getting current timestamp using
long currentTimestamp = Math.round(System.currentTimeMillis() / 1000);
How can i subtract n days from it. I am a beginner. Please help on this.

Use the Calendar class:
Calendar cal = Calendar.getInstance();
cal.add(Calendar.DAY_OF_YEAR, -5);
long fiveDaysAgo = cal.getTimeInMillis();

You can use the Calendar class in Java , use its set() method to add/subtract the required number of days from the Calendar.DATE field.
To subtract n days from today , Use c.get(Calendar.DATE)-n. Sample code :
Calendar c = Calendar.getInstance();
System.out.println(c.getTime()); // Tue Jun 18 17:07:45 IST 2013
c.set(Calendar.DATE, c.get(Calendar.DATE)-5);
System.out.println(c.getTime()); // Thu Jun 13 17:07:45 IST 2013

Date d = initDate();//intialize your date to any date
Date dateBefore = new Date(d.getTime() - n * 24 * 3600 * 1000 ); //Subtract n days
Also possible duplicate .

That currentTimestamp must be passed to a Calendar instance.
from Calendar you can subtract X days.
Get the milliseconds from calendar and is done.

You can play aorund with the following code snippet, to form it the way you want:
Calendar c = Calendar.getInstance();
c.setTimeInMillis(milliSeconds);
c.add(Calendar.DATE, -5);
Date date = c.getTime();

Calendar calendar=Calendar.getInstance();
calendar.add(Calendar.DATE, -5);
using Java.util.Calendar Class
Calendar.DATE
This is the field number for get and set indicating the day of the month. , to subtract 5 days from the current time of the calendar, you can achieve it by calling.

Try this..
long timeInMillis = System.currentTimeMillis();
Calendar cal = Calendar.getInstance();
cal.setTimeInMillis(timeInMillis);
cal.set(Calendar.DATE, cal.get(Calendar.DATE)-5);
java.util.Date date1 = cal.getTime();
System.out.println(date1);

Problems with the Date 31-12-9999 in java

My program needs to represent this date as a java.sql.date object , but it seems that when I create a new date (using the calendar) and set it to '9999-12-31' and finally convert this java.util.date object to a java.sql.date object, this date is converted to something like '000-01-31'.
Calendar calendar = Calendar.getInstance();
calendar.set(9999, 12, 31);
infinityDate = new java.sql.Date(normalizeDate(calendar.getTime()).getTime());
infinityDate should be 31-12-9999
but when my code reaches here :
if(otherDate.equals(infinityDate))
{// Do stuff}
It never goes into the if condition as the infinityDate has for some reason been changed to 31-01-000, even though otherDate is infact '31-12-9999'.
The fact that otherDate is 31-12-9999 tells me that java can represent this dates , but for some reason , when I construct it using a calendar it changes the date. (otherDate comes from a jdbc statement which fetches data from a database)
This reference date '31-12-9999' has been fixed by some client , so it cannot be changed and my program has to be able to compare some incoming date values with this.
Does anyone know why this is happening , I realize that http://en.wikipedia.org/wiki/Year_10,000_problem may be a problem for dates after year 9999 , but I should be safe by a day.
EDIT : The Normalize date method only "normalizes the given date to midnight of that day"
private static java.util.Date normalizeDate(java.util.Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
date = calendar.getTime();
return date;
}
But , this issue was appearing before I was normalizing the date , I normalized it in an attempt to fix this.

Months are zero indexed. Use 11 for December, not 12. This is why you are rolling over the year.

Calendar.MONTH is zero-based. The call
calendar.set(9999, 12, 31);
sets the date to "the 31st day in the 13th month of the year 9999", which is then implicitly converted to the 1st month of the year 10000. It would result in an exception if you first called
calendar.setLenient(false);

Check hours, minutes, seconds and milliseconds that are held into these 2 date objects. I believe they are different.
If your want to compare the date (year, month, day) only you should probably create your custom Comparator and use it.

Calendar returning the wrong time

The time displayed is way ahead of what I expected. I'm parsing a date string and turning it into milliseconds.
year = Integer.parseInt(m1.group(1));
mo = Integer.parseInt(m1.group(2));
day = Integer.parseInt(m1.group(3));
hr = Integer.parseInt(m1.group(4));
min = Integer.parseInt(m1.group(5));
sec = Integer.parseInt(m1.group(6));
and here I set the Calendar
Calendar cal = Calendar.getInstance();
cal.set(year, mo, day, hr, min, sec);
time = cal.getTimeInMillis();

If you check out the calendar documentation here, then visit here, you'll see that January is month 0. You'll want to change your code to mo = Integer.parseInt(m1.group(2))-1;

You should probably use DateFormatter to parse the date string (rather than rolling your own).
Other than that, make sure that you have the proper time zone and understand that month number one is February (not January).