Differentiating between selected items in a JComboBox

Question

As you can see below, I have created a JComboBox with elements in the 'options' array as the options in the list.

When a specific item in the list is selected, I want to display the JLabels 'one' or 'two'. E.g. selecting option one displays 'one' and selecting option two displays 'two' and removes 'one' from the display, and vice versa.

I know how to add the JLabels, with add(); but I don't know how to differentiate between which item is selected.

I have searched online and looked at the java docs but I couldn't find a relevant solution.

Thanks

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.io.*;
import java.lang.*;
import java.util.*;

public class converterPage extends JFrame {
    private JComboBox box;
    private static String[] options = {"Option one", "Option two"};
    private JLabel one, two;

    public converterPage() {
        super("Convert Units"); 
        setLayout (null);

        box = new JComboBox(options);
        box.setBounds(10, 10, 150, 30);
        add(box);

        one = new JLabel("one");
        two = new JLabel("two");
        one.setBounds(170, 10, 150, 30);
        two.setBounds(170, 10, 150, 30);


        box.addItemListener(
            new ItemListener(){ 
                public void itemStateChanged(ItemEvent event){
                    // depending on what is selected, i want to only display certain stuff 
                }   
            }        
        );
    }
}

[possible duplicate](http://stackoverflow.com/questions/58939/jcombobox-selection-change-listener) - [see this answer](http://stackoverflow.com/a/14424530/679982) it should answer your question. — linski, Jul 25 '13 at 19:27

score 1 · Answer 1 · answered Jul 25 '13 at 19:27

1

One way is to use: JComboBox#getSelectedItem().

answered Jul 25 '13 at 19:27

Eng.Fouad

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score 1 · Answer 2 · answered Jul 25 '13 at 19:27

1

You can use:

event.getItem()

to obtain an Object representing the currently selected item. The object is actually a String, becuase the combo box was created with an array of Strings.

answered Jul 25 '13 at 19:27

tbodt

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MrLore · Answer 3 · 2013-07-25T19:54:51.503

I believe this is what you're after:

import java.awt.event.*;
import java.util.HashMap;
import java.util.Map;
import javax.swing.*;

public class ConverterPage extends JFrame
{
    private JComboBox box;
    private final Map<String, JLabel> map = new HashMap<>();

    public ConverterPage()
    {
        super("Convert Units");
        super.setLayout(null);

        final JLabel one = new JLabel("one");
        final JLabel two = new JLabel("two");
        one.setBounds(170, 10, 150, 30);
        two.setBounds(170, 10, 150, 30);

        this.map.put("Option one", one);
        this.map.put("Option two", two);
        this.box = new JComboBox(this.map.keySet().toArray(new String[this.map.size()]));
        this.box.setBounds(10, 10, 150, 30);
        super.add(box);

        this.box.addItemListener(new ItemListener()
        {
            @Override
            public void itemStateChanged(ItemEvent event)
            {
                // depending on what is selected, i want to only display certain stuff 
                final JLabel label = map.get((String) event.getItemSelectable().getSelectedObjects()[0]);
                System.out.println(label.getText());
            }
        });
    }

    public static void main(String[] args)
    {
        final ConverterPage c = new ConverterPage();
        c.setSize(400, 400);
        c.setVisible(true);
    }
}

I took the liberty of cleaning up your imports (you never need to import from java.lang as it's automatically imported), and class names should really be in CapitalCase.

This prints out the selected option, e.g. 'option one', twice. When I replaced the system.out.println with add, in order to display the JLabel, it returned an error. — , Jul 25 '13 at 19:36
@user2587777 It does it twice because there are 2 events: The first item is deselected and the second option is selected (as indicated by `event.getStateChange()`. What do you mean by `add`? What was the error message? If you mean you are wanting to link "Option One" to `JLabel one`, you're going to need a map, or a switch method. — MrLore, Jul 25 '13 at 19:41
Yes I want JLabel one to display on the JFrame when "Option One" is selected, and same with JLabel two with "Option Two". — , Jul 25 '13 at 19:47
@user2587777 See edits. `label` is now the corresponding label, and you can do whatever it is you want with it from there. — MrLore, Jul 25 '13 at 19:55

Differentiating between selected items in a JComboBox

3 Answers3