How do I arrange the swing component using BoxLayout?

By Wayan in Swing 0 Comment

This example demonstrate how we can arrange component in row or column order using the BoxLayout layout manager. Instead of use the BoxLayout manager we can also use the Box component as our content pane to get the same effect as using the BoxLayout manager.

package org.kodejava.swing;

import javax.swing.*;

public class BoxLayoutDemo extends JFrame {
    public BoxLayoutDemo() {
        initialize();
    }

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

    private void initialize() {
        setSize(400, 400);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        // Set the layout of the Content Pane to BoxLayout using BoxLayout.X_AXIS
        // will arrange the component left to right. We can use the BoxLayout.Y_AXIS
        // to arrange the component top to bottom.
        setLayout(new BoxLayout(getContentPane(), BoxLayout.X_AXIS));

        JLabel label = new JLabel("Username : ");
        JTextField textField = new JTextField();

        JLabel password = new JLabel("Password :");
        JPasswordField passwordField = new JPasswordField();

        getContentPane().add(label);
        getContentPane().add(textField);

        getContentPane().add(password);
        getContentPane().add(passwordField);
    }
}

How do I determine if the menu of JComboBox is displayed?

By Wayan in Swing 0 Comment

This example show how to create an implementation of PopupMenuListener for listening to when the JComboBox menu is visible, invisible or cancelled.

package org.kodejava.swing;

import javax.swing.*;
import javax.swing.event.PopupMenuListener;
import javax.swing.event.PopupMenuEvent;
import java.awt.*;

public class ComboBoxPopupMenuListener extends JFrame {
    public ComboBoxPopupMenuListener() {
        initialize();
    }

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

    private void initialize() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        Integer[] years = new Integer[]{
                2016, 2017, 2018, 2019, 2020,
                2021, 2022, 2023, 2024, 2025
        };

        JComboBox<Integer> comboBox = new JComboBox<>(years);
        comboBox.setEditable(true);

        // Adds a PopupMenu listener which will listen to notification
        // messages from the popup portion of the combo box.
        comboBox.addPopupMenuListener(new PopupMenuListener() {
            public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
                // This method is called before the popup menu becomes visible.
                System.out.println("PopupMenuWillBecomeVisible");
            }

            public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
                // This method is called before the popup menu becomes invisible
                System.out.println("PopupMenuWillBecomeInvisible");
            }

            public void popupMenuCanceled(PopupMenuEvent e) {
                // This method is called when the popup menu is canceled
                System.out.println("PopupMenuCanceled");
            }
        });

        getContentPane().add(comboBox);
    }
}

How do I add an action listener to JComboBox?

By Wayan in Swing 0 Comment

The code below shows you how to add an ActionListener to a JComboBox component. In the snippet we add a listener by calling the addActionListener() method and give an instance of ActionListener listener as an anonymous class (a class without a specified name) as the parameter.

The ActionListener interface contract said that we must implement the actionPerformed(ActionEvent e) method. This is the place where the event will be handled by our program.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.FlowLayout;

public class ComboBoxActionListener extends JFrame {
    public ComboBoxActionListener() {
        initialize();
    }

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

    private void initialize() {
        setSize(300, 300);
        setLayout(new FlowLayout(FlowLayout.LEFT));
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        String[] names = new String[]{
                "John", "Paul", "George", "Ringo"
        };
        JComboBox<String> comboBox = new JComboBox<>(names);
        comboBox.setEditable(true);

        // Create an ActionListener for the JComboBox component.
        comboBox.addActionListener(event -> {
            // Get the source of the component, which is our combo
            // box.
            JComboBox comboBox1 = (JComboBox) event.getSource();

            // Print the selected items and the action command.
            Object selected = comboBox1.getSelectedItem();
            System.out.println("Selected Item  = " + selected);
            String command = event.getActionCommand();
            System.out.println("Action Command = " + command);

            // Detect whether the action command is "comboBoxEdited"
            // or "comboBoxChanged"
            if ("comboBoxEdited".equals(command)) {
                System.out.println("User has typed a string in " +
                        "the combo box.");
            } else if ("comboBoxChanged".equals(command)) {
                System.out.println("User has selected an item " +
                        "from the combo box.");
            }
        });
        getContentPane().add(comboBox);
    }
}

How do I listen for changes to the selected item in JComboBox?

By Wayan in Swing 0 Comment

This example demonstrates the ItemListener to listen for changes to the selected item in the JComboBox component.

package org.kodejava.swing;

import javax.swing.*;
import javax.swing.border.BevelBorder;
import java.awt.event.ItemEvent;
import java.awt.*;

public class ComboBoxSelectionChange extends JFrame {
    public ComboBoxSelectionChange() {
        initialize();
    }

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

    private void initialize() {
        setSize(300, 300);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        String[] items = new String[]{"A", "B", "C", "D", "E", "F"};
        JComboBox<String> comboBox = new JComboBox<>(items);

        final JTextArea textArea = new JTextArea(5, 15);
        textArea.setBorder(new BevelBorder(BevelBorder.LOWERED));

        // For listening to the changes of the selected items in the combo box
        // we need to add an ItemListener to the combo box component as shown
        // below.
        // Listening if a new items of the combo box has been selected.
        comboBox.addItemListener(event -> {
            // The item affected by the event.
            String item = (String) event.getItem();
            textArea.append("Affected items: " + item + "\n");
            if (event.getStateChange() == ItemEvent.SELECTED) {
                textArea.append(item + " selected\n");
            }
            if (event.getStateChange() == ItemEvent.DESELECTED) {
                textArea.append(item + " deselected\n");
            }
        });

        getContentPane().add(comboBox);
        getContentPane().add(textArea);
    }
}

How do I change the number of visible items in JComboBox?

By Wayan in Swing 1 Comment

In this example you’ll see how we can change the default number of visible items in the combo box. By default, it only shows eight items at once and when the combo box has more items a scrollbar will be shown, so we can scroll up and down in the combo box list.

If we want to change this value we can call the setMaximumRowCount(int count) of the JComboBox. Let’s see the following example for more details.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class ComboBoxMaximumRows extends JFrame {
    public ComboBoxMaximumRows() {
        initialize();
    }

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

    private void initialize() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        // Create some items for our JComboBox component. In this example we are
        // going to pass an array of string which are the name of the month.
        String[] months = {"January", "February", "March", "April", "Mei", "June",
                "July", "August", "September", "October", "November", "December"};

        // Create a month selection combo box.
        JComboBox<String> comboBox = new JComboBox<>(months);

        // By default, combo box will only show eight items in the drop-down. When
        // more than eight items are in the combo box a default scrollbar will be
        // shown. If we want to display more items we can change it by calling the
        // setMaximumRowCount() method.
        comboBox.setMaximumRowCount(12);

        getContentPane().add(comboBox);
    }
}