JComboBox and Dropdowns - potatoscript/JavaSwing GitHub Wiki

📝 JComboBox and Dropdowns in Java Swing 🎯

🎯 What is a JComboBox?

JComboBox is a component in Java Swing that allows users to select an option from a dropdown list. It displays a list of items that the user can choose from, and the user can either select an item from the list or type their own choice (if the combo box is editable).

✅ Features of JComboBox:

  • Dropdown list: Displays a list of options for users to choose from.
  • Editable: Users can type their own value (if configured as editable).
  • Single selection: Only one item can be selected at a time.

📚 Step 1: Creating a Basic JComboBox

📝 Example: Creating a Basic JComboBox 

import javax.swing.*;

public class JComboBoxExample {
    public static void main(String[] args) {
        // Create JFrame
        JFrame frame = new JFrame("JComboBox Example");

        // Create JComboBox with some items
        String[] items = {"Apple", "Banana", "Cherry", "Date", "Elderberry"};
        JComboBox<String> comboBox = new JComboBox<>(items);

        // Set layout and add JComboBox to frame
        frame.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));
        frame.add(comboBox);

        // Set frame properties
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

🎨 Explanation

✅ String[] items = {"Apple", "Banana", "Cherry", "Date", "Elderberry"};

  • This creates an array of options that will be displayed in the dropdown list.

✅ JComboBox comboBox = new JComboBox<>(items);

  • This creates a combo box with the specified items.

👩‍🎨 Output: 

+-------------------------------+
| ▼ Apple                       |
|                               |
|                               |
+-------------------------------+

🎯 Step 2: Handling JComboBox Selection

You can handle the selection event when the user selects an item from the dropdown using ActionListener.

📝 Example: Handling JComboBox Selection 

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

public class JComboBoxSelection {
    public static void main(String[] args) {
        // Create JFrame
        JFrame frame = new JFrame("JComboBox Selection");

        // Create JComboBox with some items
        String[] items = {"Apple", "Banana", "Cherry", "Date", "Elderberry"};
        JComboBox<String> comboBox = new JComboBox<>(items);

        // JLabel to display the selected item
        JLabel label = new JLabel("Selected: None");

        // Add ActionListener to update label when selection changes
        comboBox.addActionListener(e -> label.setText("Selected: " + comboBox.getSelectedItem()));

        // Set layout and add components
        frame.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));
        frame.add(comboBox);
        frame.add(label);

        // Set frame properties
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

🎨 Explanation

✅ comboBox.addActionListener(e -> label.setText("Selected: " + comboBox.getSelectedItem()));

  • When an item is selected from the combo box, the label text is updated to display the selected item.

👩‍🎨 Output: 

+-------------------------------+
| ▼ Apple                       |
|                               |
| Selected: None                |
+-------------------------------+

(When Banana is selected):
+-------------------------------+
| ▼ Banana                      |
|                               |
| Selected: Banana              |
+-------------------------------+

🎯 Step 3: Making JComboBox Editable

You can make the combo box editable so users can type their own values.

📝 Example: Creating an Editable JComboBox 

import javax.swing.*;

public class EditableJComboBox {
    public static void main(String[] args) {
        // Create JFrame
        JFrame frame = new JFrame("Editable JComboBox");

        // Create JComboBox with some items
        String[] items = {"Apple", "Banana", "Cherry", "Date", "Elderberry"};
        JComboBox<String> comboBox = new JComboBox<>(items);
        
        // Make JComboBox editable
        comboBox.setEditable(true);

        // Set layout and add JComboBox to frame
        frame.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));
        frame.add(comboBox);

        // Set frame properties
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

🎨 Explanation

✅ comboBox.setEditable(true);

  • This allows the user to type their own text in the combo box, in addition to selecting from the list.

👩‍🎨 Output: 

+-------------------------------+
| [Editable Text Field]          |
|                               |
|                               |
+-------------------------------+

🎯 Step 4: Customizing the JComboBox Appearance

You can customize the appearance of the items in the combo box by using ListCellRenderer to modify how each item is displayed.

📝 Example: Customizing Item Appearance 

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

public class CustomizedJComboBox {
    public static void main(String[] args) {
        // Create JFrame
        JFrame frame = new JFrame("Customized JComboBox");

        // Create JComboBox with items
        String[] items = {"Apple", "Banana", "Cherry", "Date", "Elderberry"};
        JComboBox<String> comboBox = new JComboBox<>(items);

        // Customize appearance with a custom renderer
        comboBox.setRenderer(new ListCellRenderer<String>() {
            @Override
            public Component getListCellRendererComponent(JList<? extends String> list, String value, int index, boolean isSelected, boolean cellHasFocus) {
                JLabel label = new JLabel(value);
                if (isSelected) {
                    label.setBackground(Color.BLUE);
                    label.setForeground(Color.WHITE);
                } else {
                    label.setBackground(Color.WHITE);
                    label.setForeground(Color.BLACK);
                }
                label.setOpaque(true);
                return label;
            }
        });

        // Set layout and add JComboBox to frame
        frame.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));
        frame.add(comboBox);

        // Set frame properties
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

🎨 Explanation

✅ comboBox.setRenderer(new ListCellRenderer() {...});

  • This customizes the appearance of each item in the combo box, changing the background and text colors when an item is selected.

👩‍🎨 Output:

  • The combo box will display with a custom style, changing color when an item is selected.
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