How do I add hours, minutes or seconds to a date?

By Wayan in Core API, Util Package 0 Comment

This example shows you how to add or subtract hours, minutes or seconds to a date using the java.util.Calendar object.

package org.kodejava.util;

import java.util.Calendar;

public class DateAddSubtract {
    public static void main(String[] args) {
        // Gets a calendar using the default time zone and locale. The
        // Calendar returned is based on the current time in the default
        // time zone with the default locale.
        Calendar calendar = Calendar.getInstance();
        System.out.println("Original = " + calendar.getTime());

        // Subtract 2 hour from the current time
        calendar.add(Calendar.HOUR, -2);

        // Add 30 minutes to the calendar time
        calendar.add(Calendar.MINUTE, 30);

        // Add 300 seconds to the calendar time
        calendar.add(Calendar.SECOND, 300);
        System.out.println("Updated  = " + calendar.getTime());
    }
}

The output of the code snippet:

Original = Wed Oct 06 19:47:53 CST 2021
Updated  = Wed Oct 06 18:22:53 CST 2021

How do I search collection elements?

By Wayan in Core API, Util Package 0 Comment

This code example use the Collections.binarySearch() to search an specified object inside a specified collections. Prior to calling the binarySearch() method we need to sort the elements of the collection. If the object is not sorted according to their natural order the search result will be undefined.

package org.kodejava.util;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Collections;
import java.text.DateFormatSymbols;

public class CollectionSearch {
    public static void main(String[] args) {
        DateFormatSymbols dfs = new DateFormatSymbols();

        LinkedList<String> monthList =
                new LinkedList<>(Arrays.asList(dfs.getMonths()));

        // Sort the collection elements
        Collections.sort(monthList);
        System.out.println("Months = " + monthList);

        // Get the position of November inside the monthList. It returns a positive
        // value if the item found in the monthList.
        int index = Collections.binarySearch(monthList, "November");
        if (index > 0) {
            System.out.println("Found at index = " + index);
            System.out.println("Month = " + monthList.get(index));
        }
    }
}

The output of the code snippet above is below.

Months = [, April, August, December, February, January, July, June, March, May, November, October, September]
Found at index = 10
Month = November

How do I rotate elements of a collection?

By Wayan in Core API, Util Package 0 Comment

This example demonstrate how to rotate the elements of a collection object. We can use the java.util.Collections class and call the rotate() method with the collection to rotate and the distance as the parameters.

package org.kodejava.util;

import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Arrays;

public class CollectionRotate {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();

        // Add some items into the collection
        for (int i = 0; i < 25; i++) {
            numbers.add(i);
        }

        // Print the collection items        
        System.out.println(Arrays.toString(numbers.toArray()));

        // Rotates the elements in the collection by the 10.
        Collections.rotate(numbers, 10);

        // Print the rotated collection items
        System.out.println(Arrays.toString(numbers.toArray()));
    }
}

Here is the program result:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]
[15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

How do I know if a date is after another date?

By Wayan in Core API, Util Package 0 Comment

This example demonstrate Date‘s class after() method to check if a date is later than another date.

package org.kodejava.util;

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

public class DateCompareAfter {
    public static void main(String[] args) {
        // Get current date
        Date today = new Date();

        // Add 1 day from the current date.
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.DATE, 1);
        Date tomorrow = calendar.getTime();

        // Tests if this date is after the specified date. This method will
        // return true if the value time represented by the tomorrow object
        // is later than today.
        if (tomorrow.after(today)) {
            System.out.println(tomorrow + " is after " + today);
        }
    }
}

The result of the code snippet above is:

Tue Oct 05 20:52:34 CST 2021 is after Mon Oct 04 20:52:33 CST 2021

How do I know if a date is before another date?

By Wayan in Core API, Util Package 0 Comment

This example demonstrate Date‘s class before() method to check if a date is earlier than another date.

package org.kodejava.util;

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

public class DateCompareBefore {
    public static void main(String[] args) {
        // Get current date
        Date today = new Date();

        // Subtract 1 day from the current date.
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.DATE, -1);
        Date yesterday = calendar.getTime();

        // Tests if this date is before the specified date. This method will
        // return true if the value time represented by the yesterday object
        // is earlier than today.
        if (yesterday.before(today)) {
            System.out.println(yesterday + " is before " + today);
        }
    }
}

The result of the code snippet above is:

Sun Oct 03 20:49:36 CST 2021 is before Mon Oct 04 20:49:36 CST 2021