如何在Java中将2个单独的组合框中的选定项放入第3个组合框中，并同时更改itemstate？

Question

I have created two comboboxes in netbeans and inserted some items into first combobox and as well into second combobox and when I want to select an item in first and second , both selected values must appear in third combobox . and if I want to change the selection in first and second also it should make the same selection in third combobox,i,e,. the item status changed .

thanks in advance and please help me, any help will be appreciated.

Answer 1

Start by taking a look at How to Use Combo Boxes and How to Write an Action Listeners for more details...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Arrays;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Combos {

    public static void main(String[] args) {
        new Combos();
    }

    public Combos() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                String[] numbers = new String[10];
                for (int index = 0; index < numbers.length; index++) {
                    numbers[index] = String.valueOf(index);
                }
                String[] letters = new String[10];
                for (int index = 0; index < letters.length; index++) {
                    letters[index] = Character.toString((char)(index + 65));
                }

                JComboBox cb1 = new JComboBox(numbers);
                JComboBox cb2 = new JComboBox(letters);

                String[] everything = new String[numbers.length + letters.length];
                System.arraycopy(numbers, 0, everything, 0, numbers.length);
                System.arraycopy(letters, 0, everything, numbers.length, letters.length);

                JComboBox cb3 = new JComboBox(everything);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new GridBagLayout());
                GridBagConstraints gbc = new GridBagConstraints();
                gbc.gridx = 0;
                gbc.gridy = 0;
                frame.add(cb1, gbc);
                gbc.gridx++;
                frame.add(cb2, gbc);

                gbc.gridx = 0;
                gbc.gridy++;
                gbc.gridwidth = GridBagConstraints.REMAINDER;
                gbc.fill = GridBagConstraints.HORIZONTAL;
                frame.add(cb3, gbc);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                cb1.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        cb3.setSelectedItem(cb1.getSelectedItem());
                    }
                });
                cb2.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        cb3.setSelectedItem(cb2.getSelectedItem());
                    }
                });
            }
        });
    }

}

Updated

Okay, so basically, for the third JComboBox , you need to combine the contents of the other two into a single unified model, for example...

String combined[] = new String[numbers.length * letters.length];
int index = 0;
for (int outter = 0; outter < numbers.length; outter++) {
    for (int inner = 0; inner < numbers.length; inner++) {
        combined[index] = numbers[outter] + " " + letters[inner];
        index++;
    }
}

Then, when either of the first two change, you can combine the results and use that as the selected item in the third...

protected void updateCombinedView() {
    String value = cb1.getSelectedItem() + " " + cb2.getSelectedItem();
    cb3.setSelectedItem(value);
}

I still have no idea why, but there you are...

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Combos {

    public static void main(String[] args) {
        new Combos();
    }

    private JComboBox<String> cb1;
    private JComboBox<String> cb2;
    private JComboBox<String> cb3;

    public Combos() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                String[] numbers = new String[10];
                for (int index = 0; index < numbers.length; index++) {
                    numbers[index] = String.valueOf(index);
                }
                String[] letters = new String[10];
                for (int index = 0; index < letters.length; index++) {
                    letters[index] = Character.toString((char) (index + 65));
                }

                String combined[] = new String[numbers.length * letters.length];
                int index = 0;
                for (int outter = 0; outter < numbers.length; outter++) {
                    for (int inner = 0; inner < numbers.length; inner++) {
                        combined[index] = numbers[outter] + " " + letters[inner];
                        index++;
                    }
                }

                cb1 = new JComboBox(numbers);
                cb2 = new JComboBox(letters);

                cb3 = new JComboBox(combined);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new GridBagLayout());
                GridBagConstraints gbc = new GridBagConstraints();
                gbc.gridx = 0;
                gbc.gridy = 0;
                frame.add(cb1, gbc);
                gbc.gridx++;
                frame.add(cb2, gbc);

                gbc.gridx = 0;
                gbc.gridy++;
                gbc.gridwidth = GridBagConstraints.REMAINDER;
                gbc.fill = GridBagConstraints.HORIZONTAL;
                frame.add(cb3, gbc);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                cb1.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        updateCombinedView();
                    }
                });
                cb2.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        updateCombinedView();
                    }
                });
            }
        });
    }

    protected void updateCombinedView() {
        String value = cb1.getSelectedItem() + " " + cb2.getSelectedItem();
        cb3.setSelectedItem(value);
    }

}