This question already has answers here:
Does Java support Julian calendar?
(4 answers)
Closed 5 years ago.
I need to create a program that reads dates from a .csv file and convert it so that 13 days are added. I already did that but somehow it does not add the following dates as wished. It also goes over 30 days, which is not supposed to happen for example 2001-12-42.
public static void main(String[] args) throws FileNotFoundException, ParseException {
File fread = new File("src/daten-greg.csv");
File fwrite = new File("src/daten-jul.csv");
Scanner s = new Scanner(fread);
PrintStream print = new PrintStream(fwrite);
while(s.hasNext()) {
String[] line = s.nextLine().split(" ");
print.println(String.join(" ", Convert(line)));
}
s.close();
print.close();
}
private static String[] Convert(String[] value) throws ParseException {
for (int i = 0; i < value.length; i+=1)
value[i] = ToJulianisch(value[i]);
return value;
}
private static String ToJulianisch(String date) throws ParseException {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd");
Date d = sdf.parse(date);
Calendar c = Calendar.getInstance();
c.setTime(d);
int actDay = c.get(Calendar.DAY_OF_MONTH);
int actMonth = c.get(Calendar.MONTH) + 1 ;
int actYear = c.get(Calendar.YEAR);
actDay -= 13;
if(actDay - 13 < 1) {
actMonth -= 1;
if(actMonth < 1) {
actMonth = 12;
actYear -= 1;
}
Calendar k = Calendar.getInstance();
k.set(Calendar.YEAR, actYear);
k.set(Calendar.MONTH, actMonth - 1);
actDay = k.getActualMaximum(Calendar.DAY_OF_MONTH) + actDay;
}
return String.format("%s-%s-%s", actYear, actMonth, actDay);
}
You are subtracting 13 from actDay twice, first in actDay-=13 and again for if(actDay - 13 < 1). Inside the if block, you then add the value which is less than 14 to the number of days per month, resulting in overflowing the day of month.
If you simply want to subtract 13 days from the given date, you should use c.set(Calendar.DAY_OF_MONTH,actDay-13). This will handle the subtraction correctly inside the Calendar object and you can then use
actDay = c.get(Calendar.DAY_OF_MONTH);
int actMonth = c.get(Calendar.MONTH) + 1 ;
int actYear = c.get(Calendar.YEAR);
return String.format("%s-%s-%s", actYear, actMonth, actDay);
About some mistakes in your algorithm, see the answer of Heikki Mäenpää. I have also seen another mistake, namely a wrong pattern "yyyy-mm-dd" where "mm" stands for minutes (use "MM" for months).
But in general, you seem to try to reinvent the wheel. Even the old java.util.Calendar-API has a built-in way for the transformation from a gregorian to a julian calendar date, see my solution which is valid even for any date in the past with respect to cutover.
Your solution is only valid for dates where the distance between gregorian and julian calendar is 13 days (which is not true in the past, at the time of Pope Gregor's reform, there were only 10 days cut off).
public static void main(String[] args) throws ParseException {
String input = "2017-10-24";
System.out.println("Old API => " + toJulianisch(input)); // 2017-10-11
}
private static String toJulianisch(String date) throws ParseException {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
sdf.setTimeZone(TimeZone.getTimeZone("GMT"));
GregorianCalendar gcal = new GregorianCalendar();
gcal.setTimeZone(TimeZone.getTimeZone("GMT"));
gcal.setGregorianChange(new Date(Long.MIN_VALUE));
sdf.setCalendar(gcal);
Date d = sdf.parse(date);
gcal.setGregorianChange(new Date(Long.MAX_VALUE));
gcal.setTime(d);
return sdf.format(d);
}
As you can see, the old API-stuff even forces you to set the timezone to a fixed offset to avoid any possible timezone clutter. This is necessary because java.util.Calendar and java.util.Date are not real calendar dates but instants/moments.
Side notice:
I have written a time library (Time4J) which can even handle any historic date equal if it was gregorian or julian (or even swedish), equal when the historic year started (was in most cases not the first of January!) etc. Maybe it is overkill for your problem but I mention it for the case you really want to operate with true historic calendar dates.
Related
this code below gets the current time and timezone of the area
Date date = new Date();
DateFormat df = new SimpleDateFormat("HH:mm:ss");
df.setTimeZone(TimeZone.getDefault());
System.out.println("Time: " + df.format(date));
right now its 1:01 pm (at the time of typing)
what i need help doing is implementing a feature in the code that checks if the current time has passed, for example 1:00PM
but I have no idea where to even start, can you help me out?
Use the Java 8+ Time API class LocalTime:
LocalTime refTime = LocalTime.of(13, 0); // 1:00 PM
// Check if now > refTime, in default time zone
LocalTime now = LocalTime.now();
if (now.isAfter(refTime)) {
// passed
}
// Check if now >= refTime, in pacific time zone
LocalTime now = LocalTime.now(ZoneId.of("America/Los_Angeles"))
if (now.compareTo(refTime) >= 0) {
// passed
}
I see it has already answered with Time, but as a teaching point, if you really wanted to use Date, you could have done something like this:
public static void main(String[] args) {
Date date = new Date();
DateFormat df = new SimpleDateFormat("HH:mm:ss");
df.setTimeZone(TimeZone.getDefault());
System.out.println("Time: " + df.format(date));
//If you print the date you'll see how it is formatted
//System.out.println(date.toString());
//So you can just split the string and use the segment you want
String[] fullDate = date.toString().split(" ");
String compareAgainstTime = "01:00PM";
System.out.println(isPastTime(fullDate[3],compareAgainstTime));
}
public static boolean isPastTime(String currentTime, String comparedTime) {
//We need to make the comparison time into the same format as the current time: 24H instead of 12H:
//then we'll just convert the time into only minutes to that we can more easily compare;
int comparedHour = comparedTime[-2].equals("AM") ? String.valueOf(comparedTime[0:2]) : String.valueOf(comparedTime[0:2] + 12 );
int comparedMin = String.valueOf(comparedTime[3:5]);
int comparedT = comparedHour*60 + comparedMin;
//obviously currentTime is alredy the correct format; just need to convert to minutes
int currentHour = String.valueOf(currentTime[0:2]);
int currentMin = String.valueOf(currentTime[3:5]);
int currentT = currentHour*60 + currentMin;
return (currentT > comparedT);
}
It's a bit messier, having to muddy into the Strings and whatnot, but it is possible. You would also have to be careful the zero-pad the comparedTime or just check for that in the function
Apparently in a simple problem but I am being complicated with the treatment of dates. I need a date comparator that receives as parameters a date in yyyy-MM-dd format and a number (age) and that determines if it is above that number or below.
For example for 18, 1999-01-01 is above and would return true, but for 2010-01-01 false. If it were the year 2001, it would compare with the current month and year, that is, 2001-06-18 that was greater or less
I have this code using the gregorian api for the current date but I am unable.
I have this done
public static void main (String args[]) throws ParseException{
//SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
//Date fechaInicial=(Date) dateFormat.parse("1999-01-01");
java.sql.Datedate1 = new Date(1999-01-01);
Calendar date2 = Calendar.getInstance();
boolean res = date(date1, date2);
}
public static boolean date(java.sql.Datedate1, Calendar date2 ){
//int year=18;
int y= date2.get(Calendar.YEAR)-18;
int m = date2.get(Calendar.MONTH)+1;
int d = date2.get(Calendar.DAY_OF_MONTH);
System.out.println(
String fechacompleta= y+"-"+m+"-"+d;
System.out.println(fechacompleta);
return ;
}
You can write your date method using java.time.LocalDate like this:
public static boolean date(LocalDate ld, int age) {
Period p = Period.between(ld, LocalDate.now());
return p.getYears() >= age;
}
It computes the Period between a certain date and now, and returns whether that period is greater than or equal to 18 years.
You can create a LocalDate like this:
LocalDate ld = LocalDate.parse("2001-12-23", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
And pass it into date:
if (date(ld, 18)) {
// 18 or above!
}
How can the year in the output add up according to the month's summation?
int sewa = 10
Calendar now = Calendar.getInstance();
int year = now.get(Calendar.YEAR);
String cyear = Integer.toString(year);
int mont = (now.get(Calendar.MONTH) + 1);
String cmont = Integer.toString(mont);
int day = (now.get(Calendar.DATE) );
String cday = Integer.toString(day);
String date = cyear +"/"+cmont+"/"+cday;
Calendar ex = Calendar.getInstance();
int exyear = ex.get(Calendar.YEAR);
String excyear = Integer.toString(exyear);
ex.add(Calendar.MONTH,+sewa);
int exmont = (ex.get(Calendar.MONTH) + 1);
String excmont = Integer.toString(exmont);
int exday = (ex.get(Calendar.DATE) );
String excday = Integer.toString(exday);
String exdate = excyear +"/"+excmont+"/"+excday;
System.out.println(date);
System.out.println("+++++");
System.out.println(exdate);
now : 2018/3/25
+++++ after:2018/1/25
how ouput :2019/1/25
If you are using Java 8 or newer version, please use LocalDate instead of Calendar class. It's very easy to add days, months and years using methods plusDays(), plusMonths() and plusYears(). It's that simple:
LocalDate today = LocalDate.now();
today.plusDays(20);
today.plusMonths(1);
today.plusYears(5);
LocalDate and LocalDateTime were introduced with JSR-310 as much simpler, straightforward and easy to use replacement of Date and Calendar.
However, if you use older version of java, or need to use Date and Calendar for some other reason, you can increase the number of years the same way you did with the months, using
ex.add(Calendar.YEAR, 5);
You capture the year to a variable ...
int exyear = ex.get(Calendar.YEAR);
String excyear = Integer.toString(exyear);
... right before you add 10 months to the calendar ...
ex.add(Calendar.MONTH,+sewa);
... which causes the excyear remains not updated.
To solve it, give the statements a correct order (Get Calendar -> add the months -> get Strings -> print). Or better using SimpleDateFormat:
Calendar ex = Calendar.getInstance();
ex.add(Calendar.MONTH, sewa);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd");
String exdate = sdf.format(ex.getTime());
System.out.println(exdate);
Prints out:
2019/01/25
I have an application that plugs into the Google Fit Api and returns the steps for the last 7 days, the method is below. As the screen shot shows though I wish to add the day to the step count.
I have tried many options to take away one day at a time for the 7 loop but had no luck, it just says the same day. Any help would be great thank you.
private void dumpDataSet(DataSet dataSet) {
Log.i(TAG, "Data returned for Data type: " + dataSet.getDataType().getName());
DateFormat dateFormat = DateFormat.getTimeInstance();
int i = 0;
for (DataPoint dp : dataSet.getDataPoints()) {
for(Field field : dp.getDataType().getFields()) { //loop 7 times
int test = dp.getValue(field).asInt();
String weekSteps= String.valueOf(test); //get weekday steps one at a time
SimpleDateFormat sdf = new SimpleDateFormat("EEEE");
Calendar cal = Calendar.getInstance();
String weekday = sdf.format(cal.getTime());
String weekStepsFinal= weekSteps + " steps on " + weekday; //set Textfield to steps and the day
FeedItem item = new FeedItem();
item.setTitle(weekStepsFinal);
feedItemList.add(item);
}
}
}
There are 7 datasets btw.
If by "take away one day at a time" means that you want the days going backwards, then here's how:
SimpleDateFormat sdf = new SimpleDateFormat("EEEE");
System.out.println("Last 7 days (starting today):");
Calendar cal = Calendar.getInstance(); // Initialized to today/now
for (int i = 0; i < 7; i++) {
System.out.println(" " + sdf.format(cal.getTime()));
cal.add(Calendar.DAY_OF_MONTH, -1); // Update to previous day at same time-of-day
}
OUTPUT
Last 7 days (starting today):
Monday
Sunday
Saturday
Friday
Thursday
Wednesday
Tuesday
This will subtract 7 days from the calendar to get you the date 7 days ago:
Calendar cal = Calendar.getInstance();
cal.add(Calendar.DAY_OF_MONTH, -7).
To subtract one day use the following code :
int DAY_IN_MILLIS = 1000 * 60 * 60 * 24;
Date currentDate = new Date();
long previousDay = currentDate.getTime()-DAY_IN_MILLIS;
SimpleDateFormat sdf = new SimpleDateFormat("EEEE");
String day = sdf.format(previousDay);
I have a string holding a start time and an end time in this format 8:30AM - 9:30PM I want to be able to strip out the AM - and the PM and convert all the times to 24 hour format so 9:30PM would really be 21:30 and also have both the times stored in 2 different variables, I know how to strip the string into substrings but Im not sure about the conversion, this is what I have so far. the time variable starts out holding 8:30AM - 9:30PM.
String time = strLine.substring(85, 110).trim();
//time is "8:30AM - 9:30PM"
String startTime;
startTime = time.substring(0, 7).trim();
//startTime is "8:30AM"
String endTime;
endTime = time.substring(9).trim();
//endTime "9:30AM"
Working code (considering that you managed to split the Strings):
public class App {
public static void main(String[] args) {
try {
System.out.println(convertTo24HoursFormat("12:00AM")); // 00:00
System.out.println(convertTo24HoursFormat("12:00PM")); // 12:00
System.out.println(convertTo24HoursFormat("11:59PM")); // 23:59
System.out.println(convertTo24HoursFormat("9:30PM")); // 21:30
} catch (ParseException ex) {
Logger.getLogger(App.class.getName()).log(Level.SEVERE, null, ex);
}
}
// Replace with KK:mma if you want 0-11 interval
private static final DateFormat TWELVE_TF = new SimpleDateFormat("hh:mma");
// Replace with kk:mm if you want 1-24 interval
private static final DateFormat TWENTY_FOUR_TF = new SimpleDateFormat("HH:mm");
public static String convertTo24HoursFormat(String twelveHourTime)
throws ParseException {
return TWENTY_FOUR_TF.format(
TWELVE_TF.parse(twelveHourTime));
}
}
Now that I think about it, SimpleDateFormat, H h K k can be confusing.
Cheers.
You need to use: SimpleDateFormat
And can refer this tutorial: Formatting hour using SimpleDateFormat
Example:
//create Date object
Date date = new Date();
//formatting hour in h (1-12 in AM/PM) format like 1, 2..12.
String strDateFormat = "h";
SimpleDateFormat sdf = new SimpleDateFormat(strDateFormat);
System.out.println("hour in h format : " + sdf.format(date));
I wouldn't reinvent the wheel (unless you are doing this as a school project or some such).
Just get a date object out of your time stamp and then you can generate whatever format you want with this: SimpleDateFormat
[edited to address your specific request]
if you absolutely need to work from your own unique strings, then you'll do something like this (I don't know exactly what your strings look like... you're using offsets like 85, which means nothing out of context).
I didn't check this for bugs, but this is approximately what you want...
myStr = timestampString.toLowerCase(); //something like 8:30am
boolean add12 = (myStr.indexOf("pm") != -1)?true:false;
//convert hour to int
int hour = Integer.parseInt(myStr.split(":")[0]);
int minutes = Integer.parseInt( myStr.split(":")[1].replaceAll("\\D+","").replaceAll("^0+","") ); //get the letters out of the minute part and get a number out of that, also, strip out leading zeros
int militaryTime = hour + (add12)? 12:0;
if(!add12 && militaryTime == 12)
militaryTime = 0; //account for 12am
//dont' forget to add the leading zeros back in as you assemble your string
With Joda Time, the code looks like:
DateTimeFormatter formatter12 = DateTimeFormat.forPattern("K:mma");
DateTime begin = formatter12.parseDateTime(beginTime);
DateTime end = formatter12.parseDateTime(endTime);
DateTimeFormatter formatter24 = DateTimeFormat.forPattern("k:mma");
String begin24 = formatter24.print(begin);
String end24 = formatter24.print(end);
I should like to contribute the modern answer
DateTimeFormatter twelveHourFormatter = DateTimeFormatter.ofPattern("h:mma", Locale.ENGLISH);
String time = "8:30AM - 9:30PM";
String[] times = time.split(" - ");
LocalTime start = LocalTime.parse(times[0], twelveHourFormatter);
System.out.println(start.toString());
LocalTime end = LocalTime.parse(times[1], twelveHourFormatter);
System.out.println(end.toString());
This prints:
08:30
21:30
I am using java.time, the modern Java date and time API. The SimpleDateFormat class used in many of the other answers is long outdated and was always troublesome. java.time is so much nicer to work with than the date-time classes from the 1990’s. A LocalTime is a time of day without a date (and without time zone), so suits your need much better than an old-fashioned Date.
Link: Oracle tutorial: Date Time explaining how to use java.time.
24 hour time adds 12 to any time greater than 12pm so that 1pm is 13 and so on until 24 or 12am. Here is the sudo code:
if(hour <= 12)
{
hour = hour + 12;
}
All the below lines will works when
String str="07:05:45PM";
and when you call timeConversion(str) and want to convert to 24 hours format..
public class TimeConversion {
private static final DateFormat TWELVE_TF = new SimpleDateFormat("hh:mm:ssa");
private static final DateFormat TWENTY_FOUR_TF = new SimpleDateFormat("HH:mm:ss");
static String timeConversion(String s) {
String str = null;
try {
str= TWENTY_FOUR_TF.format(
TWELVE_TF.parse(s));
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return str;
}
public static void main(String[] args) throws ParseException {
String str="07:05:45PM";
System.out.println(timeConversion(str));
}
}