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 to Install Consolas Font in Mac OS X?

By Wayan in OS X 0 Comment

Here are the instructions to install Microsoft Consolas Font on Mac OS X.

  • You need to install brew first.
  • Type-in the following commands.
brew install cabextract
cd ~/Downloads
mkdir Consolas
cd Consolas
curl -LO https://sourceforge.net/projects/mscorefonts2/files/cabs/PowerPointViewer.exe
cabextract PowerPointViewer.exe
cabextract ppviewer.cab
open CONSOLA*.TTF
  • Press Install Font button to install the fonts.

How do I clear the current command line in terminal?

By Wayan in Tools, Ubuntu 0 Comment
Terminal

You have typed a long line of command in terminal. But now you want to clear or delete the entire line. Deleting each character in the command will take sometime and bored you. So are there any keyboard shortcuts that allow you to do this? Yes there are some hotkeys to the rescue.

Hotkeys Description
CTRL + u Delete the current command.
The deleted command will be stored into a buffer.
CTRL + w Delete a word.
CTRL + c Abort what you are typing.
CTRL + d Delete current character.

Other hotkeys that might help you work faster in the terminal.

Hotkeys Description
CTRL + e Move to the end of line.
CTRL + a Move to the start of line.
CTRL + k Cut text from the cursor to the end of line.
CTRL + y Paste the last cut text or buffer.
CTRL + - Undo.
CTRL + b Backward one character.
CTRL + f Forward one character.
ALT + ← Backward one word.
ALT + → Forward one word.

How do I generate random alphanumeric strings?

By Wayan in Apache Commons, Commons Text 0 Comment

The following code snippet demonstrates how to use RandomStringGenerator class from the Apache Commons Text library to generate random strings. To create an instance of the generator we can use the RandomStringGenerator.Builder() class build() method. The builder class also helps us to configure the properties of the generator. Before calling the build() method we can set the properties of the builder using the following methods:

  • withinRange() to specifies the minimum and maximum code points allowed in the generated string.
  • filteredBy() to limits the characters in the generated string to those that match at least one of the predicates supplied. Some enum for the predicates: CharacterPredicates.DIGITS, CharacterPredicates.LETTERS.
  • selectFrom() to limits the characters in the generated string to those who match at supplied list of Character.
  • usingRandom() to overrides the default source of randomness.

After configuring and building the generator based the properties defined, we can generate the random strings using the generate() methods of the RandomStringGenerator. There are two methods available:

  • generate(int length) generates a random string, containing the specified number of code points.
  • generate(int minLengthInclusive, int maxLengthInclusive) generates a random string, containing between the minimum (inclusive) and the maximum (inclusive) number of code points.

And here is your code snippet:

package org.kodejava.commons.text;

import org.apache.commons.text.CharacterPredicates;
import org.apache.commons.text.RandomStringGenerator;

public class RandomStringDemo {
    public static void main(String[] args) {
        RandomStringGenerator generator = new RandomStringGenerator.Builder()
                .withinRange('0', 'z')
                .filteredBy(CharacterPredicates.DIGITS, CharacterPredicates.LETTERS)
                .build();

        for (int i = 0; i < 10; i++) {
            System.out.println(generator.generate(10, 20));
        }
    }
}

Below are examples of generated random alphanumeric strings:

weJDtVARLIFS96WXje
FYrNzTR3Q3dUrLT3Xsc
4F1fu8nSsA
nIQi3a4Oyv9
l6QcsP9bejdbaLd2jd
Cc9YgTfgwo
2B8un8YCcxn9m2
RAN2dZAWalUIWeZeoS
jPQspicyaKfAzS14twH
GTurc0lWkSid03rG0JZ

Apache Logo

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-text</artifactId>
    <version>1.12.0</version>
</dependency>

Maven Central

Why do I get ArrayIndexOutOfBoundsException in Java?

By Wayan in Basic, Lang Package 1 Comment

The ArrayIndexOutOfBoundsException exception is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.

Array with 10 elements

For example see the code snippet below:

String[] vowels = new String[]{"a", "i", "u", "e", "o"}
String vowel = vowels[10]; // throws the ArrayIndexOutOfBoundsException

Above we create a vowels array with five elements. This will make the array have indexes between 0..4. On the next line we tried to access the tenth element of the array which is illegal. This statement will cause the ArrayIndexOutOfBoundsException thrown.

We must understand that arrays in Java are zero indexed. The first element of the array will be at index 0 and the last element will be at index array-size - 1. So be careful with your array indexes when accessing array elements. For example if you have an array with 5 elements this mean that the index of the array is from 0 to 4.

If you are trying to iterate an array using for loop. Make sure the index start from 0 and execute the loop while the index is less than the length of the array, you can get the length of the array using the array length property. Let’s see the code snippet below:

for (int i = 0; i < vowels.length; i++) {
    String vowel = vowels[i];
    System.out.println("vowel = " + vowel);
}

Or if you don’t need the index you can simplify your code using the for-each or enhanced for-loop statement instead of the classic for loop statement as shown below:

for (String vowel : vowels) {
    System.out.println("vowel = " + vowel);
}