java - Sharing same model between two JComboBoxes

Question

I have a Person [ ] with three Persons (p1,p2,p3). Person class has two attributes name and email.

I want to add all names of Person[] in one JComboBox and all emails in another JComboBox.

I used the following code.

    Person p1 = new Person("Smith", "[email protected]");
    Person p2 = new Person("Tom", "[email protected]");
    Person p3 = new Person("John","[email protected]");

    Person[] per_arr = new Person[] { p1, p2, p3};

    JFrame frame = new JFrame();
    JPanel panel = new JPanel();
    JComboBox<String> combo1 = new JComboBox<String>();
    JComboBox<String> combo2 = new JComboBox<String>();

    for (Person p : per_arr) {
        combo1.addItem(p.getName());
        combo2.addItem(p.getEmail());
    }
    panel.add(combo1);
    panel.add(combo2);
    frame.setContentPane(panel);
    frame.pack();
    frame.setVisible(true);

But I don't want to used like this. I'd like to use the two combo boxes with the same model. I tried with DefaultComboBoxModel and Override getElementAt() method like the following.

public class MyModel extends DefaultComboBoxModel<Object> {

public MyModel(Object[] items) {
    super(items);
}

@Override
public Object getElementAt(int index) {
    if (super.getElementAt(index) instanceof Person) {
        return (Person)super.getElementAt(index);
    } else {
        return null;
    }
}

}

The above ComboBoxModel give me only the Person objects.

The Question is how can I add all names of Person[] in one JComboBox and all emails in another JComboBox using same ComboBoxModel .

Answer 1

Use one instance of ComboBoxModel and two instances of JComboBox, each having the same model. Let each JComboBox have a custom renderer that displays the desired Person attribute for that JComboBox.

In the example below, each combo gets its own instance of a single renderer that implements the strategy pattern, passing a Function<Person, String> that selects the correct attribute when the renderer is called:

DefaultComboBoxModel model = new DefaultComboBoxModel(…);
JComboBox<String> combo1 = new JComboBox<>(model);
combo1.setRenderer(new PersonRenderer(Person::getName));
JComboBox<String> combo2 = new JComboBox<>(model);
combo2.setRenderer(new PersonRenderer(Person::getEmail));

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.util.function.Function;
import javax.swing.DefaultComboBoxModel;
import javax.swing.DefaultListCellRenderer;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;

/**
 * @see http://stackoverflow.com/a/37222598/230513
 */
public class ComboRendererTest {

    private void display() {
        JFrame f = new JFrame("Test");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLayout(new FlowLayout());
        DefaultComboBoxModel model = new DefaultComboBoxModel(new Person[]{
            new Person("Alpher", "[email protected]"),
            new Person("Bethe", "[email protected]"),
            new Person("Gammow", "[email protected]")});
        JComboBox<String> combo1 = new JComboBox<>(model);
        combo1.setRenderer(new PersonRenderer(Person::getName));
        JComboBox<String> combo2 = new JComboBox<>(model);
        combo2.setRenderer(new PersonRenderer(Person::getEmail));
        f.add(combo1);
        f.add(combo2);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private static class PersonRenderer extends DefaultListCellRenderer {

        Function<Person, String> personAttribute;

        public PersonRenderer(Function<Person, String> personAttribute) {
            this.personAttribute = personAttribute;
        }

        @Override
        public Component getListCellRendererComponent(JList<?> list, Object
            value, int index, boolean isSelected, boolean cellHasFocus) {
            JLabel l = (JLabel) super.getListCellRendererComponent(
                list, value, index, isSelected, cellHasFocus);
            Person p = (Person) value;
            l.setText(personAttribute.apply(p));
            return l;
        }
    }

    private static class Person {

        private final String name;
        private final String email;

        public Person(String name, String email) {
            this.name = name;
            this.email = email;
        }

        public String getName() {
            return name;
        }

        public String getEmail() {
            return email;
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new ComboRendererTest()::display);
    }
}