How to Create Dynamic JComboBoxes with Dependent Selections in Java?

Dynamic JComboBoxes: Populating Dependent ComboBox based on Selection

Introduction

The goal is to create two dynamic JComboBoxes where the option list in one changes depending on the selected item in the other. This is useful when representing hierarchical data, such as courses and subjects.

Solution

To implement this functionality, follow these steps:

1. Create a DefaultComboBoxModel for Each Set:

   Create separate DefaultComboBoxModels for each set of options, such as courses and subjects. For example:

   DefaultComboBoxModel coursesModel = new DefaultComboBoxModel(new String[] {"Course 1", "Course 2", "Course 3"});
   DefaultComboBoxModel subjectsModel1 = new DefaultComboBoxModel(new String[] {"A1", "A2"});
   DefaultComboBoxModel subjectsModel2 = new DefaultComboBoxModel(new String[] {"B1", "B2", "B3", "B4"});

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2. Set the Initial Model for JComboBox2:

   Set the initial ComboBoxModel for JComboBox2 to the first set of options (in this case, subjects from Course 1).

   combo2.setModel(subjectsModel1);

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3. Handle the Selection Event in JComboBox1:

   Add an ActionListener to JComboBox1 to monitor selection changes. When the user selects a course, update the ComboBoxModel of JComboBox2 with the corresponding subjects for that course.

   combo1.addActionListener(new ActionListener() {
       @Override
       public void actionPerformed(ActionEvent e) {
           int i = combo1.getSelectedIndex();
           combo2.setModel(subjectsModels[i]);
       }
   });

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Example Implementation

The following code snippet demonstrates the implementation of the solution:

import javax.swing.ComboBoxModel;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class DynamicCombos extends JPanel {

    public DynamicCombos() {
        ComboBoxModel[] models = new ComboBoxModel[3];

        models[0] = new DefaultComboBoxModel(new String[] {"Course 1", "Course 2", "Course 3"});
        models[1] = new DefaultComboBoxModel(new String[] {"A1", "A2"});
        models[2] = new DefaultComboBoxModel(new String[] {"B1", "B2", "B3", "B4"});

        JComboBox combo1 = new JComboBox(models[0]);
        JComboBox combo2 = new JComboBox(models[1]);

        combo1.addActionListener(e -> combo2.setModel(models[combo1.getSelectedIndex()]));

        add(combo1);
        add(combo2);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new DynamicCombos());
        frame.pack();
        frame.setVisible(true);
    }
}

Conclusion

By leveraging DefaultComboBoxModels and event handling, this solution allows for dynamic population of JComboBoxes based on the selection in another JComboBox. This technique is particularly useful in situations where data is organized hierarchically and needs to be represented in a user-friendly interface.

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