How do I use the double brace initialization?

By Wayan in Basic, Core API 0 Comment

The double brace initialization {{ ... }} is another way for initializing a collection objects in Java. It is offer a simple syntax for initializing a collection object.

package org.kodejava.lang;

import java.util.ArrayList;
import java.util.List;

public class DoubleBraceInitialization {
    public static void main(String[] args) {
        // Creates a list of colors and add three colors of
        // Red, Green and Blue.
        List<String> colors1 = new ArrayList<>();
        colors1.add("Red");
        colors1.add("Green");
        colors1.add("Blue");

        for (String color : colors1) {
            System.out.println("Color = " + color);
        }

        // Creates another list of colors and add three colors
        // using the double brace initialization.
        List<String> colors2 = new ArrayList<>() {{
            add("Red");
            add("Green");
            add("Blue");
        }};

        for (String color : colors2) {
            System.out.println("Color = " + color);
        }
    }
}

What’s actually happened is: the first brace creates an anonymous inner class and the second brace is an initializer block. Due to the need for creating an inner class the use of double brace initialization is considered to be slower.

Because of this performance issue it’s better not to use this technique for your production code, but using it in your unit testing can make your test looks simpler.

How do I count the number of occurrences of a char in a String?

By Wayan in Core API, Lang Package 0 Comment

This example show you how to count the number of a character occurrences in a string. We show two ways to do it, using the String.replaceAll(String regex, String replace) method and creating a loop that check every char in the String and count the matched char.

package org.kodejava.lang;

public class CharCounter {
    public static void main(String[] args) {
        String text = "a,b,c,c,e,f,g,g,g,g,h";

        // Use the CharCounter.countCharOccurrences() method to count.
        int numberOfLetterC = CharCounter.countCharOccurrences(text, 'c');
        System.out.println("Letter c = " + numberOfLetterC);

        // Other solution is to use the String.replaceAll() method. We'll
        // replace the chars other than the counted char with an empty string.
        // To get the char occurrences we count the length of the remaining
        // string.
        int numberOfComma = text.replaceAll("[^,]", "").length();
        System.out.println("Comma    = " + numberOfComma);

        int numberOfLetterG = text.replaceAll("[^g]", "").length();
        System.out.println("Letter g = " + numberOfLetterG);
    }

    /**
     * Count number of specified char occurrences in the specified string.
     */
    private static int countCharOccurrences(String source, char target) {
        int counter = 0;

        // Loop through the string and increment the counter if the
        // target character found in the string. 
        for (int i = 0; i < source.length(); i++) {
            if (source.charAt(i) == target) {
                counter++;
            }
        }
        return counter;
    }
}

How do I count number of weekday between two dates?

By Wayan in Core API, Util Package 0 Comment

The code below helps you find the number of a specified weekday (Monday, Tuesday, Wednesday, etc.) between two dates. The solution we used below is to loop between the two dates and check if the weekday of those dates are equals to the day we want to count.

package org.kodejava.util;

import java.util.Calendar;

public class DaysBetweenDate {
    public static void main(String[] args) {
        Calendar start = Calendar.getInstance();
        start.set(2021, Calendar.OCTOBER, 1);
        Calendar end = Calendar.getInstance();
        end.set(2021, Calendar.OCTOBER, 31);

        System.out.print("Number Monday between " +
                start.getTime() + " and " + end.getTime() + " are: ");

        int numberOfDays = 0;
        while (start.before(end)) {
            if (start.get(Calendar.DAY_OF_WEEK) == Calendar.MONDAY) {
                numberOfDays++;
                start.add(Calendar.DATE, 7);
            } else {
                start.add(Calendar.DATE, 1);
            }
        }

        System.out.println(numberOfDays);
    }
}

The result of our program is:

Number Monday between Fri Oct 01 07:55:06 CST 2021 and Sun Oct 31 07:55:06 CST 2021 are: 4

How do I set Swing Timer initial delay?

By Wayan in Swing 0 Comment

The Swing javax.swing.Timer object fires the action event after the delay time specified in the constructor passed. For some reasons you might want the Timer class fires immediately after it was started.

To achieve this you can set the timer initial delay by calling the setInitialDelay(int initialDelay) method. The example below give you an example how to do it.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class TimerInitialDelayDemo extends JFrame {
    private final JLabel counterLabel = new JLabel();

    private Timer timer = null;

    public TimerInitialDelayDemo() throws HeadlessException {
        initUI();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(
                () -> new TimerInitialDelayDemo().setVisible(true));
    }

    private void initUI() {
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setSize(500, 500);

        Container container = getContentPane();
        container.setLayout(new FlowLayout(FlowLayout.CENTER));
        container.add(counterLabel);

        timer = new Timer(1000, new MyActionListener());

        // Set initial delay of the Timer object. Setting initial delay
        // to zero causes the timer fires the event immediately after
        // it is started.
        timer.setInitialDelay(0);
        timer.start();
    }

    class MyActionListener implements ActionListener {
        private int counter = 10;

        public void actionPerformed(ActionEvent e) {
            counter = counter - 1;
            String text = "<html><font size='14'>" +
                    counter +
                    "</font></head>";
            counterLabel.setText(text);
            if (counter == 0) {
                timer.stop();
            }
        }
    }
}

How do I use Swing Timer class?

By Wayan in Swing 0 Comment

In this example you’ll see how to use java.swing.Timer class to create a text clock program.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;
import java.util.Calendar;
import java.text.DateFormat;
import java.text.SimpleDateFormat;

public class TimerDemo extends JFrame {
    public static final DateFormat df = new SimpleDateFormat("hh:mm:ss");

    public TimerDemo() throws HeadlessException {
        initUI();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new TimerDemo().setVisible(true));
    }

    private void initUI() {
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setSize(500, 500);

        Container container = getContentPane();
        container.setLayout(new FlowLayout(FlowLayout.CENTER));

        final JLabel label = new JLabel();
        container.add(label);

        Timer timer = new Timer(1000, e -> {
            Calendar now = Calendar.getInstance();
            String timeText =
                    "<html><font size='10' color='blue'>" +
                            df.format(now.getTime()) +
                            "</font></html>";
            label.setText(timeText);
        });
        timer.start();
    }
}