What is my mistake to convert Date into minutes?

Question

Based on How to convert Standard Date into minutes in java? information, I follow this technique to convert date into minute, but an output is not as an expected value (e.g., 12 hour -> it should be 720 minutes).

Here is my source code

    SimpleDateFormat sdf = new SimpleDateFormat("hh");
    Date theDate = sdf.parse ("12");
    long minutes22 = (theDate.getTime() / 1000)  / 60;
    System.out.println("Minute "+minutes22);

An output is -420. Can someone explain to me ?

< First problem is solved, please take a look at the comment section >

The new problem is cutting String. < The problem is solved as well,please take a look at comment section >

For Another Input that I have try to do my own solution,but there is problem occur after finishing cutting String. I found that duplicate value can not keep separately. I don t know why would happen because I kept in different index. Any suggestion ?

Here is another my another source code.

    String date = "Sun 10:00-20:00\r\n" + 
            "Fri 05:00-10:00\r\n" + 
            "Fri 16:30-23:50\r\n" + 
            "Sat 10:00-24:00\r\n" + 
            "Sun 01:00-04:00\r\n" + 
            "Sat 02:00-06:00\r\n" + 
            "Tue 03:30-18:15\r\n" + 
            "Tue 19:00-20:00\r\n" + 
            "Wed 04:25-15:14\r\n" + 
            "Wed 15:14-22:40\r\n" + 
            "Thu 00:00-23:59\r\n" + 
            "Mon 05:00-13:00\r\n" + 
            "Mon 15:00-21:00";

    List<String> Hour = new ArrayList<String>();
    int loop = 0;

    String [] replacement = {"sun","mon","tue","wed","thu","fri","sat"};
    String new_s = date.toLowerCase().replaceAll(" ","");

    for(int j = 0;j<replacement.length;j++)
    {
        new_s = new_s.replace(replacement[j],"").replace("\r\n","");


    }

    String temp = "";
    temp = temp+new_s.replaceAll("-","");

    int show = 0;
    while(!temp.equals(""))
    {
        Hour.add(temp.substring(loop,loop+5));
        temp = temp.replace(temp.substring(0,loop+5),"");
        System.out.println("Hour "+Hour.get(show));
        show++;

    }

Here is the output

Hour 10:00 Hour 20:00 Hour 05:00 Hour 16:30 Hour 23:50 Hour 24:00 Hour 01:00 Hour 04:00 Hour 02:00 Hour 06:00 Hour 03:30 Hour 18:15 Hour 19:00 Hour 04:25 Hour 15:14 Hour 22:40 Hour 00:00 Hour 23:59 Hour 13:00 Hour 15:00 Hour 21:00

Another question - why would it print out < 0 instead of 1200 >

 LocalTime froms = LocalTime.parse("20:00", DateTimeFormatter.ofPattern("HH:mm", Locale.ENGLISH));
System.out.println("TIme "+froms.getMinute());'

Answer 1

tl;dr

Duration.ofHours(12).toMinutes()

720

java.time.Duration

You are using troubled old legacy date-time classes. And furthermore, you are abusing by them.

The Date class has been replaced by the Instant class. Both represent a moment, a point on the timeline. Do not abuse them to represent “twelve hours”.

Apparently you want to represent a span of time unattached to the timeline. So use the class designed for that purpose, Duration.

Duration d = Duration.ofHours(12);

To see the total number of minutes in the entire duration, call toMinutes.

long minutes = d.toMinutes();

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Answer 2

    String input = "Sun 11:00-20:00";
    String[] fromAndTo = input.split("-");
    LocalTime from = LocalTime.parse(fromAndTo[0], DateTimeFormatter.ofPattern("EEE H:mm", Locale.ENGLISH));
    LocalTime to = LocalTime.parse(fromAndTo[1]);
    System.out.println(Duration.between(from, to).toMinutes());

This printed:

540

Can someone explain to me ?

You’ve got two bugs that both contribute to your incorrect result:

• You misused a Date for a duration and didn’t specify time zone.
• You used lowercase hh for hours in you format pattern string. hh is for hour within AM or PM from 01 through 12, so 12 means the same as 0 (because 12:00 AM is the same as 00:00 on a 24-hour clock).

Your SimpleDateFormat understood 12 as 00:00 in your local time zone (as defined by your JVM’s time zone setting). However, when you take out the milliseconds using theDate.getTime(), you get the milliseconds since 00:00 in UTC. Since your time zone has an offset from UTC, you get an error the magnitude of this offset.