How do I reverse a string, words or sentences?

By Wayan in Apache Commons, Commons Lang 0 Comment 
package org.kodejava.commons.lang;

import org.apache.commons.lang3.StringUtils;

public class StringReverseDemo {
    public static void main(String[] args) {
        // We have an original string here that we'll need to reverse.
        String words = "The quick brown fox jumps over the lazy dog";

        // Using StringUtils.reverse we can reverse the string letter by letter.
        String reversed = StringUtils.reverse(words);

        // Now we want to reverse per word, we can use
        // StringUtils.reverseDelimited() method to do this.
        String delimitedReverse = StringUtils.reverseDelimited(words, ' ');

        // Print out the result
        System.out.println("Original: " + words);
        System.out.println("Reversed: " + reversed);
        System.out.println("Delimited Reverse: " + delimitedReverse);
    }
}

Here is the result:

Original: The quick brown fox jumps over the lazy dog
Reversed: god yzal eht revo spmuj xof nworb kciuq ehT
Delimited Reverse: dog lazy the over jumps fox brown quick The

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version>
</dependency>

Maven Central

How do I check if a string is empty or not?

By Wayan in Apache Commons, Commons Lang 0 Comment 
package org.kodejava.commons.lang;

import org.apache.commons.lang3.StringUtils;

public class EmptyStringCheckDemo {
    public static void main(String[] args) {
        // Create some variable to hold some empty string, contains only
        // whitespaces and words.
        String one = "";
        String two = "\t\r\n";
        String three = "     ";
        String four = null;
        String five = "four four two";

        // We can use StringUtils class for checking if a string is empty or not
        // using StringUtils.isBlank() method. This method will return true if
        // the tested string is empty, contains whitespaces only or null.
        System.out.println("Is one empty? " + StringUtils.isBlank(one));
        System.out.println("Is two empty? " + StringUtils.isBlank(two));
        System.out.println("Is three empty? " + StringUtils.isBlank(three));
        System.out.println("Is four empty? " + StringUtils.isBlank(four));
        System.out.println("Is five empty? " + StringUtils.isBlank(five));

        // On the other side, the StringUtils.isNotBlank() methods complement
        // the previous method. It will check if a tested string is not empty.
        System.out.println("Is one not empty? " + StringUtils.isNotBlank(one));
        System.out.println("Is two not empty? " + StringUtils.isNotBlank(two));
        System.out.println("Is three not empty? " + StringUtils.isNotBlank(three));
        System.out.println("Is four not empty? " + StringUtils.isNotBlank(four));
        System.out.println("Is five not empty? " + StringUtils.isNotBlank(five));
    }
}

Here is the result:

Is one empty? true
Is two empty? true
Is three empty? true
Is four empty? true
Is five empty? false
Is one not empty? false
Is two not empty? false
Is three not empty? false
Is four not empty? false
Is five not empty? true

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version>
</dependency>

Maven Central

How do I convert Date to String?

By Wayan in Core API, Text Package 1 Comment 
package org.kodejava.text;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Calendar;
import java.util.Date;

public class DateToString {
    public static void main(String[] args) {
        // Create an instance of SimpleDateFormat used for formatting
        // the string representation of date (day/month/year)
        String pattern = "dd/MM/yyyy";
        DateFormat df = new SimpleDateFormat(pattern);

        // Get the date today using Calendar object.
        Date today = Calendar.getInstance().getTime();

        // Using DateFormat format method we can create a string
        // representation of a date with the defined format.
        String reportDate = df.format(today);

        // Print what date is today!
        System.out.println("Report Date: " + reportDate);

        // Using Java 8.
        // Creates a DateTimeFormatter using the ofPattern() method. Get
        // the current date by calling the .now() method of LocalDate.
        // To convert to string use the format() method of the LocalDate
        // and pass the formatter object as argument.
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
        LocalDate now = LocalDate.now();
        reportDate = now.format(formatter);
        System.out.println("Report Date: " + reportDate);
    }
}

How do I get day of week?

By Wayan in Core API, Util Package 0 Comment

In this example we want to create a calendar or date from a year and day of the year. Next we will find out what day-of-week that calendar or date represent. In the code snippet below we are trying to find the 180 day of the year 2021.

Let’s see the example below.

package org.kodejava.util;

import java.text.DateFormatSymbols;
import java.util.Calendar;

public class DayOfYearToDayOfWeekExample {
    public static void main(String[] args) {
        // Create a calendar with year and day of year.
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.YEAR, 2021);
        calendar.set(Calendar.DAY_OF_YEAR, 180);

        // See the full information of the calendar object.
        System.out.println(calendar.getTime().toString());

        // Get the weekday and print it
        int weekday = calendar.get(Calendar.DAY_OF_WEEK);
        System.out.println("Weekday: " + weekday);

        // Get weekday name
        DateFormatSymbols dfs = new DateFormatSymbols();
        System.out.println("Weekday: " + dfs.getWeekdays()[weekday]);
    }
}

Below is the result of our program.

Tue Jun 29 06:04:21 CST 2021
Weekday: 3
Weekday: Tuesday

How do I convert Array to Collection?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.Arrays;
import java.util.List;

public class ArrayToListExample {
    public static void main(String[] args) {
        // Creates an array of object, in this case we create an
        // Integer array.
        Integer[] numbers = {1, 1, 2, 3, 5, 8, 13, 21, 34, 55};

        // Convert the created array above to collection, in this
        // example we convert it to a List.
        List<Integer> list = Arrays.asList(numbers);

        // We've got a list of our array here and iterate it.
        for (Integer number : list) {
            System.out.print(number + ", ");
        }
    }
}

How do I convert collection to ArrayList?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.ArrayList;
import java.util.LinkedList;

public class CollectionToArrayList {
    public static void main(String[] args) {
        // We create LinkedList collection type at put some values
        // in it. Here we put A, B, C and D letter into it.
        LinkedList<String> linkedList = new LinkedList<>();
        linkedList.push("A");
        linkedList.push("B");
        linkedList.push("C");
        linkedList.push("D");

        // Let say you want to convert it to other type of collection,
        // for instance here we convert it into ArrayList. To do it
        // we can pass the collection created above as a parameter to
        // ArrayList constructor.
        ArrayList<String> arrayList = new ArrayList<>(linkedList);

        // Now we have converted the collection into ArrayList and
        // printed what is inside.
        for (String s : arrayList) {
            System.out.println("s = " + s);
        }
    }
}

How do I get number of days in a month?

By Wayan in Core API, Util Package 3 Comments

Let say you want to know the number of days in a month, or we can say it as the last date of a month. The example below shows you how to obtain the number of days or the date.

package org.kodejava.util;

import java.util.Calendar;

public class MonthDaysExample {
    public static void main(String[] args) {
        // First get an instance of calendar object.
        Calendar calendar = Calendar.getInstance();

        // We'll set the date of the calendar to the following
        // date. We can use constant variable in the calendar
        // for months value (JANUARY - DECEMBER). Be informed that
        // month in Java started from 0 instead of 1.
        int year = 2021;
        int month = Calendar.FEBRUARY;
        int date = 1;
        // We have a new date of 2021-02-01
        calendar.set(year, month, date);

        // Here we get the maximum days for the date specified
        // in the calendar. In this case we want to get the number
        // of days for february 2021
        int maxDay = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
        System.out.println("Max Day: " + maxDay);

        // Here we want to see what is the days for february on
        // a leap year.
        calendar.set(2020, Calendar.FEBRUARY, 1);
        maxDay = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
        System.out.println("Max Day: " + maxDay);
    }
}

The result of the code snippet above:

Max Day: 28
Max Day: 29

In JDK 8 you can use the new Date Time API to get the number of days in a month. Here an example that show you how to do it: How do I get the length of month represented by a date object?.

How do I create random number?

By Wayan in Core API, Lang Package 1 Comment

The java.lang.Math.random() method returns random number between 0.0 and 1.0 including 0.0 but not including 1.0. By multiplying Math.random() result with a number, for example 10 will give us a range of random number between 0.0 and 10.0.

To get a random number between two numbers (n and m) we can use the formula of: n + (Math.random() * (m - n)). Where n is the lowest number (inclusive) and m is the highest number (exclusive).

package org.kodejava.lang;

public class RandomNumberExample {
    public static void main(String[] args) {
        // The Math.random() returns a random number between 0.0 and 1.0 
        // including 0.0 but not including 1.0.
        double number = Math.random();
        System.out.println("Generated number: " + number);

        // By multiplying Math.random() result with a number will give
        // us a range of random number between, for instance 0.0 to 10.0 as
        // shown in the example below.
        number = Math.random() * 10;
        System.out.println("Generated number: " + number);

        // To get a random number between n and m we can use the formula:
        // n + (Math.random() * (m - n)). The example below creates random
        // number between 100.0 and 200.0.
        int n = 100;
        int m = 200;
        number = n + (Math.random() * (m - n));
        System.out.println("Generated number: " + number);

        // Creates an integer random number
        int random = 100 + (int) (Math.random() * 100);
        System.out.println("Generated number: " + random);
    }
}

Here is an example result of our program.

Generated number: 0.024974902600698234
Generated number: 2.271051510086771
Generated number: 147.542543014888
Generated number: 112

How do I query records from a table?

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

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class JdbcQueryExample {
    // Database connection information
    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) {
        // Get a connection to database.
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            // Create a statement object.
            Statement statement = connection.createStatement();

            // Executes a query command to select isbn and the book title
            // from books table. The execute query returns a ResultSet
            // object which is the result of our query execution.
            String query = "SELECT isbn, title, published_year FROM book";
            ResultSet books = statement.executeQuery(query);

            // To get the value returned by the statement.executeQuery we
            // need to iterate the books object until the last items.
            while (books.next()) {
                // To get the value from the ResultSet object we can call
                // a method that correspond to the data type of the column
                // in database table. In the example below we call
                // books.getString("isbn") to get the book's ISBN 
                // information.
                System.out.println(books.getString("isbn") + ", " +
                        books.getString("title") + ", " +
                        books.getInt("published_year"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central

How do I get my screen size?

By Wayan in AWT, Core API 0 Comment 
package org.kodejava.awt;

import java.awt.*;

public class ScreenSizeExample {
    public static void main(String[] args) {
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

        System.out.println("Screen Width: " + screenSize.getWidth());
        System.out.println("Screen Height: " + screenSize.getHeight());
    }
}

The output of the code snippet above:

Screen Width: 2560.0
Screen Height: 1080.0