How do I set the time of java.util.Date instance to 00:00:00?

By Wayan in Core API, Util Package 1 Comment

The following code snippet shows you how to remove time information from the java.util.Date object. The static method removeTime() in the code snippet below will take a Date object as parameter and will return a new Date object where the hour, minute, second and millisecond information hasbeen reset to zero. To do this, we use the java.util.Calendar. To remove time information, we set the calendar fields of Calendar.HOUR_OF_DAY, Calendar.MINUTE, Calendar.SECOND and Calendar.MILLISECOND to zero.

package org.kodejava.util;

import java.util.Calendar;
import java.util.Date;

public class DateRemoveTime {
    public static void main(String[] args) {
        System.out.println("Now = " + removeTime(new Date()));
    }

    private static Date removeTime(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);
        return calendar.getTime();
    }
}

The result of the code snippet above is:

Now = Sat Nov 20 00:00:00 CST 2021

In the above code:

  1. An instance of Calendar is created using Calendar.getInstance().
  2. We set the Calendar time using setTime() method and pass the date object.
  3. The time fields (HOUR_OF_DAY, MINUTE, SECOND, MILLISECOND) are set to zero. Calendar.HOUR_OF_DAY is used for 24-hour clock.
  4. The resulting Calendar instances time value is printed which should now represent the start of the day.

How do I find the difference between two times?

By Wayan in Java Date Time API 0 Comment

The following code snippet show you how to find the difference between two time objects represented by LocalTime class. To get the difference between two LocalTime objects we can use the Duration.between() method. This method returns a Duration object, to get the difference in seconds we call the getSeconds() method.

Here a code snippet to demonstrate it.

package org.kodejava.datetime;

import java.time.*;

public class TimeDifference {
    public static void main(String[] args) {
        LocalTime start = LocalTime.now();
        LocalTime end = LocalTime.of(16, 59, 55);
        Duration duration = Duration.between(start, end);

        System.out.printf("Seconds between %s and %s is: %s seconds.%n",
                start, end, duration.getSeconds());

        diffLocalDateTime();
        diffInstant();
    }

    /**
     * Difference between two LocalDateTime objects.
     */
    public static void diffLocalDateTime() {
        LocalDateTime dt1 = LocalDateTime.now();
        LocalDateTime dt2 = LocalDateTime.now(ZoneId.of("GMT+0"));
        Duration duration = Duration.between(dt1, dt2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }

    /**
     * Difference between two Instant objects.
     */
    public static void diffInstant() {
        Instant instant1 = Instant.now();
        Instant instant2 = Instant.EPOCH;
        Duration duration = Duration.between(instant1, instant2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }
}

Using the Duration.between() we can also get the difference between two LocalDateTime objects and two Instant object as seen in the diffLocalDateTime() method and diffInstant method in the code snippet above.

The result of the code snippet:

Seconds between 15:05:35.401317900 and 16:59:55 is: 6859 seconds.
Duration = -28800 seconds.
Duration = -1637132736 seconds.

How do I format a message that contains time information?

By Wayan in Core API, Text Package 0 Comment

Here we demonstrate how to use the java.text.MessageFormat class to format a message contains time information.

package org.kodejava.text;

import java.util.Date;
import java.util.Calendar;
import java.util.Locale;
import java.text.MessageFormat;

public class MessageFormatTime {
    public static void main(String[] args) {
        Date today = new Date();
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.HOUR, 7);

        Date next7Hours = calendar.getTime();

        // We want the message to be is Locale.US
        Locale.setDefault(Locale.US);

        // Format a time including date information.
        String message = MessageFormat.format("Now is {0} and the next " +
                "7 hours is {1}", today, next7Hours);
        System.out.println(message);

        // Format a time and display only the time portion
        message = MessageFormat.format("Now is {0, time} and the next " +
                "7 hours is {1, time}", today, next7Hours);
        System.out.println(message);

        // Format a time using a short format (e.g. HH:mm am/pm)
        message = MessageFormat.format("Now is {0, time, short} and " +
                "the next 7 hours is {1, time, short}", today, next7Hours);
        System.out.println(message);

        // Format a time using a medium format (eg. HH:mm:ss am/pm).
        message = MessageFormat.format("Now is {0, time, medium} and " +
                "the next 7 hours is {1, time, medium}", today, next7Hours);
        System.out.println(message);

        // Format a time using a long format (e.g. HH:mm:ss am/pm TIMEZONE).
        message = MessageFormat.format("Now is {0, time, long} and the " +
                "next 7 hours is {1, time, long}", today, next7Hours);
        System.out.println(message);

        // Format a time using a full format (e.g. HH:mm:ss am/pm TIMEZONE).
        message = MessageFormat.format("Now is {0, time, full} and the " +
                "next 7 hours is {1, time, full}", today, next7Hours);
        System.out.println(message);

        // Format a time using a custom pattern.
        message = MessageFormat.format("Now is {0, time, HH:mm:ss.sss} " +
                "and the next 7 hours is {1, time, HH:mm:ss.sss}", today, next7Hours);
        System.out.println(message);
    }
}

The above program produces:

Now is 10/8/21, 9:38 PM and the next 7 hours is 10/9/21, 4:38 AM
Now is 9:38:10 PM and the next 7 hours is 4:38:10 AM
Now is 9:38 PM and the next 7 hours is 4:38 AM
Now is 9:38:10 PM and the next 7 hours is 4:38:10 AM
Now is 9:38:10 PM CST and the next 7 hours is 4:38:10 AM CST
Now is 9:38:10 PM China Standard Time and the next 7 hours is 4:38:10 AM China Standard Time
Now is  21:38:10.010 and the next 7 hours is  04:38:10.010

How do I get date time functions supported by database?

By Wayan in JDBC 0 Comment 
package org.kodejava.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.DatabaseMetaData;
import java.sql.SQLException;

public class DateTimeFunction {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            DatabaseMetaData meta = connection.getMetaData();

            // Get date and time functions supported by database
            String[] functions = meta.getTimeDateFunctions().split(",\\s*");

            for (String function : functions) {
                System.out.println("Function = " + function);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Date and time functions supported by MySQL database.

Function = DAYOFWEEK
Function = WEEKDAY
Function = DAYOFMONTH
Function = DAYOFYEAR
Function = MONTH
Function = DAYNAME
Function = MONTHNAME
Function = QUARTER
Function = WEEK
Function = YEAR
Function = HOUR
Function = MINUTE
Function = SECOND
Function = PERIOD_ADD
Function = PERIOD_DIFF
Function = TO_DAYS
Function = FROM_DAYS
Function = DATE_FORMAT
Function = TIME_FORMAT
Function = CURDATE
Function = CURRENT_DATE
Function = CURTIME
Function = CURRENT_TIME
Function = NOW
Function = SYSDATE
Function = CURRENT_TIMESTAMP
Function = UNIX_TIMESTAMP
Function = FROM_UNIXTIME
Function = SEC_TO_TIME
Function = TIME_TO_SEC

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.1.0</version>
</dependency>

Maven Central

How do I convert string of time to time object?

By Wayan in Core API, Util Package 1 Comment

You want to convert a string representing a time into a time object in Java. As we know that Java represents time information in a class java.util.Date, this class keep information for date and time.

Now if you have a string of time like 15:30:18, you can use a SimpleDateFormat object to parse the string time and return a java.util.Date object. The pattern of the string should be passed to the SimpleDateFormat constructor. In the example below the string is formatted as hh:mm:ss (hour:minute:second).

package org.kodejava.util;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

public class StringToTimeExample {
    public static void main(String[] args) {        
        // A string of time information
        String time = "15:30:18";

        // Create an instance of SimpleDateFormat with the specified
        // format.
        DateFormat sdf = new SimpleDateFormat("hh:mm:ss");
        try {
            // To get the date object from the string just called the 
            // parse method and pass the time string to it. This method 
            // throws ParseException if the time string is invalid. 
            // But remember as we don't pass the date information this 
            // date object will represent the 1st of january 1970.
            Date date = sdf.parse(time);            
            System.out.println("Date and Time: " + date);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The code snippet above print the following output:

Date and Time: Thu Jan 01 15:30:18 CST 1970