How do I add key listener event handler to JTextField?

By Wayan in Swing 3 Comments

In this small Swing code snippet we demonstrate how to use java.awt.event.KeyAdapter abstract class to handle keyboard event for the JTextField component. The snippet will change the characters typed in the JTextField component to uppercase.

A better approach for this use case is to use the DocumentFilter class. See the following code snippet How do I format JTextField text to uppercase?.

package org.kodejava.swing;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.HeadlessException;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

public class UppercaseTextFieldDemo extends JFrame {
    public UppercaseTextFieldDemo() throws HeadlessException {
        initComponents();
    }

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

    protected void initComponents() {
        // Set default form size, closing event and layout manager
        setSize(500, 500);
        setTitle("JTextField Key Listener");
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        getContentPane().setLayout(new FlowLayout(FlowLayout.LEFT));

        // Create a label and text field for our demo application and add the
        // component to the frame content pane object.
        JLabel usernameLabel = new JLabel("Username: ");
        JTextField usernameTextField = new JTextField();
        usernameTextField.setPreferredSize(new Dimension(150, 20));
        getContentPane().add(usernameLabel);
        getContentPane().add(usernameTextField);

        // Register a KeyListener for the text field. Using the KeyAdapter class
        // allow us implement the only key listener event that we want to listen,
        // in this example we use the keyReleased event.
        usernameTextField.addKeyListener(new KeyAdapter() {
            public void keyReleased(KeyEvent e) {
                JTextField textField = (JTextField) e.getSource();
                String text = textField.getText();
                textField.setText(text.toUpperCase());
            }
        });
    }
}
JTextField Key Listener

JTextField Key Listener

How do I change JFrame image icon?

By Wayan in Swing 0 Comment

This code snippet demonstrates how to change a JFrame image icon using the setIconImage() method.

package org.kodejava.swing;

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.WindowConstants;
import java.awt.Dimension;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;

public class FrameIconExample extends JFrame {
    public static void main(String[] args) {
        FrameIconExample frame = new FrameIconExample();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        // Set the window size and its title
        frame.setSize(new Dimension(500, 500));
        frame.setTitle("Frame Icon Example");

        // Read the image that will be used as the application icon.
        // Using "/" in front of the image file name will locate the
        // image at the root folder of our application. If you don't
        // use a "/" then the image file should be on the same folder
        // with your class file.
        try {
            URL resource = frame.getClass().getResource("/logo.png");
            BufferedImage image = ImageIO.read(resource);
            frame.setIconImage(image);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Display the form
        frame.setVisible(true);
    }
}
Change JFrame Image Icon

Change JFrame Image Icon

How do I use Console class to read user input?

By Wayan in Core API, IO 0 Comment

In the previous example, How do I read user input from console using Scanner class?, we use the java.util.Scanner class to read user input. In this example we use another new class introduced in the Java 1.6, the java.io.Console class.

The Console class provide methods like readLine() and readPassword(). The readPassword() method can be used to read user’s password. Using this method the user’s input will not be shown in the console. The password will be returned as an array of char.

package org.kodejava.io;

import java.io.Console;

public class ConsoleDemo {

    public static void main(String[] args) {
        // Get a console object, console can be null if not available.
        Console console = System.console();

        if (console == null) {
            System.out.println("Console is not available.");
            System.exit(1);
        }

        // Read username from the console
        String username = console.readLine("Username: ");

        // Read password, the password will not be echoed to the
        // console screen and returned as an array of characters.
        char[] password = console.readPassword("Password: ");

        if (username.equals("admin") && String.valueOf(password).equals("secret")) {
            console.printf("Welcome to Java Application %1$s.%n", username);
        } else {
            console.printf("Invalid username or password.%n");
        }
    }
}

The result of the code snippet above is:

Username: admin
Password:
Welcome to Java Application admin.

How do I read user input from console using java.util.Scanner class?

By Wayan in Core API, Util Package 1 Comment

In JDK 1.5 a java.util.Scanner class was introduced to handle user input in console application. This class enable us to read string, integer, long, etc.

package org.kodejava.util;

import java.util.Scanner;

public class ScannerDemo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Read string input for username
        System.out.print("Username: ");
        String username = scanner.nextLine();

        // Read string input for password
        System.out.print("Password: ");
        String password = scanner.nextLine();

        // Read an integer input for another challenge
        System.out.print("What is 2 + 2: ");
        int result = scanner.nextInt();

        if (username.equals("admin")
                && password.equals("secret") && result == 4) {
            System.out.println("Welcome to Java Application");
        } else {
            System.out.println("Invalid username or password, " +
                    "access denied!");
        }
    }
}

The result of the code snippet:

Username: admin
Password: secret
What is 2 + 2: 4
Welcome to Java Application

How do I use ResourceBundle for i18n?

By Wayan in Core API, Util Package 0 Comment

Creating an application for users in different regions can be hard in terms of the message format for the local region. Java provide a ResourceBundle class that help internationalize our application.

To create resources for i18n (there are 18 letters between the first i and the final n) we need to create a file for each locale our application supported. The file name must be ended in language_COUNTRY.properties. For instance a resource bundle for Locale.UK will be MessagesBundle_en_GB.properties.

When the bundle has been loaded we can use bundle.getString(key) to read specific message from our resource bundle file.

package org.kodejava.util;

import java.util.Locale;
import java.util.ResourceBundle;

public class InternationalizationDemo {

    public static void main(String[] args) {
        // Load resource bundle for Locale.UK locale. The resource 
        // bundle will load the MessagesBundle_en_GB.properties file.
        ResourceBundle bundle =
                ResourceBundle.getBundle("MessagesBundle", Locale.UK);
        System.out.println("Message in " + Locale.UK + ": " +
                bundle.getString("greeting"));

        // Change the default locale to Indonesian and get the default 
        // resource bundle for the current locale.
        Locale.setDefault(new Locale("in", "ID"));
        bundle = ResourceBundle.getBundle("MessagesBundle");
        System.out.println("Message in " + Locale.getDefault() + ": " +
                bundle.getString("greeting"));
    }
}

Below are some example of our resource bundle files, these files should be located in our application classpath to enable the ResourceBundle class to read it.

MessagesBundle_en_GB.properties

greeting=Hello, how are you?

MessagesBundle_in_ID.properties

greeting=Halo, apa kabar?