Java Swing | JComboBox with examples

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JComboBox is a part of Java Swing package. JComboBox inherits JComponent class . JComboBox shows a popup menu that shows a list and the user can select a option from that specified list . JComboBox can be editable or read- only depending on the choice of the programmer .
Constructor of the JComboBox are:

JComboBox() : creates a new empty JComboBox .
JComboBox(ComboBoxModel M) : creates a new JComboBox with items from specified ComboBoxModel
JComboBox(E [ ] i) : creates a new JComboBox with items from specified array.
JComboBox(Vector items) : creates a new JComboBox with items from the specified vector

Commonly used Methods are :

addItem(E item) : adds the item to the JComboBox
addItemListener( ItemListener l) : adds a ItemListener to JComboBox
getItemAt(int i) : returns the item at index i
getItemCount(): returns the number of items from the list
getSelectedItem() : returns the item which is selected
removeItemAt(int i) : removes the element at index i
setEditable(boolean b) : the boolean b determines whether the combo box is editable or not .If true is passed then the combo box is editable or vice versa.
setSelectedIndex(int i): selects the element of JComboBox at index i.
showPopup() :causes the combo box to display its popup window.
setUI(ComboBoxUI ui): sets the L&F object that renders this component.
setSelectedItem(Object a): sets the selected item in the combo box display area to the object in the argument.
setSelectedIndex(int a): selects the item at index anIndex.
setPopupVisible(boolean v): sets the visibility of the popup.
setModel(ComboBoxModel a) : sets the data model that the JComboBox uses to obtain the list of items.
setMaximumRowCount(int count): sets the maximum number of rows the JComboBox displays.
setEnabled(boolean b): enables the combo box so that items can be selected.
removeItem(Object anObject) : removes an item from the item list.
removeAllItems(): removes all items from the item list.
removeActionListener(ActionListener l): removes an ActionListener.
isPopupVisible() : determines the visibility of the popup.
addPopupMenuListener(PopupMenuListener l) : adds a PopupMenu listener which will listen to notification messages from the popup portion of the combo box.
getActionCommand() : returns the action command that is included in the event sent to action listeners.
getEditor(): returns the editor used to paint and edit the selected item in the JComboBox field.
getItemCount() : returns the number of items in the list.
getItemListeners(): returns an array of all the ItemListeners added to this JComboBox with addItemListener().
createDefaultKeySelectionManager() : returns an instance of the default key-selection manager.
fireItemStateChanged(ItemEvent e) : notifies all listeners that have registered interest for notification on this event type.
firePopupMenuCanceled() : notifies PopupMenuListeners that the popup portion of the combo box has been canceled.
firePopupMenuWillBecomeInvisible() : notifies PopupMenuListeners that the popup portion of the combo box has become invisible.
firePopupMenuWillBecomeVisible() : notifies PopupMenuListeners that the popup portion of the combo box will become visible.
setEditor(ComboBoxEditor a): sets the editor used to paint and edit the selected item in the JComboBox field.
setActionCommand(String a) : sets the action command that should be included in the event sent to actionListeners.
getUI() : returns the look and feel object that renders this component.
paramString() : returns a string representation of this JComboBox.
getUIClassID() : returns the name of the Look and feel class that renders this component.
getAccessibleContext() : gets the AccessibleContext associated with this JComboBox

The following programs will illustrate the use of JComboBox
1. Program to create a simple JComboBox and add elements to it .

Java

// Java Program to create a simple JComboBox
// and add elements to it
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
class solve extends JFrame implements ItemListener {
 
    // frame
    static JFrame f;
 
    // label
    static JLabel l, l1;
 
    // combobox
    static JComboBox c1;
 
    // main class
    public static void main(String[] args)
    {
        // create a new frame
        f = new JFrame("frame");
 
        // create a object
        solve s = new solve();
 
        // set layout of frame
        f.setLayout(new FlowLayout());
 
        // array of string containing cities
        String s1[] = { "Jalpaiguri", "Mumbai", "Noida", "Kolkata", "New Delhi" };
 
        // create checkbox
        c1 = new JComboBox(s1);
 
        // add ItemListener
        c1.addItemListener(s);
 
        // create labels
        l = new JLabel("select your city ");
        l1 = new JLabel("Jalpaiguri selected");
 
        // set color of text
        l.setForeground(Color.red);
        l1.setForeground(Color.blue);
 
        // create a new panel
        JPanel p = new JPanel();
 
        p.add(l);
 
        // add combobox to panel
        p.add(c1);
 
        p.add(l1);
 
        // add panel to frame
        f.add(p);
 
        // set the size of frame
        f.setSize(400, 300);
 
        f.show();
    }
    public void itemStateChanged(ItemEvent e)
    {
        // if the state combobox is changed
        if (e.getSource() == c1) {
 
            l1.setText(c1.getSelectedItem() + " selected");
        }
    }
}

Output :

2. Program to create two checkbox one editable and other read only

Java

// Java Program to create two  checkbox
// one editable and other read only
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
class solve extends JFrame implements ItemListener {
 
    // frame
    static JFrame f;
 
    // label
    static JLabel l, l1, l3, l4;
 
    // combobox
    static JComboBox c1, c2;
 
    // main class
    public static void main(String[] args)
    {
        // create a new frame
        f = new JFrame("frame");
 
        // create a object
        solve s = new solve();
 
        // array of string containing cities
        String s1[] = { "Jalpaiguri", "Mumbai", "Noida", "Kolkata", "New Delhi" };
        String s2[] = { "male", "female", "others" };
 
        // create checkbox
        c1 = new JComboBox(s1);
        c2 = new JComboBox(s2);
 
        // set Kolkata and male as selected items
        // using setSelectedIndex
        c1.setSelectedIndex(3);
        c2.setSelectedIndex(0);
 
        // add ItemListener
        c1.addItemListener(s);
        c2.addItemListener(s);
 
        // set the checkbox as editable
        c1.setEditable(true);
 
        // create labels
        l = new JLabel("select your city ");
        l1 = new JLabel("Jalpaiguri selected");
        l3 = new JLabel("select your gender ");
        l4 = new JLabel("Male selected");
 
        // set color of text
        l.setForeground(Color.red);
        l1.setForeground(Color.blue);
        l3.setForeground(Color.red);
        l4.setForeground(Color.blue);
 
        // create a new panel
        JPanel p = new JPanel();
 
        p.add(l);
 
        // add combobox to panel
        p.add(c1);
 
        p.add(l1);
 
        p.add(l3);
 
        // add combobox to panel
        p.add(c2);
 
        p.add(l4);
 
        // set a layout for panel
        p.setLayout(new FlowLayout());
 
        // add panel to frame
        f.add(p);
 
        // set the size of frame
        f.setSize(400, 400);
 
        f.show();
    }
    public void itemStateChanged(ItemEvent e)
    {
        // if the state combobox 1is changed
        if (e.getSource() == c1) {
 
            l1.setText(c1.getSelectedItem() + " selected");
        }
 
        // if state of combobox 2 is changed
        else
            l4.setText(c2.getSelectedItem() + " selected");
    }
}

Output :

3. Program to create a checkbox and add or remove items from it .

Java

// Java  Program to create a checkbox
// and add or remove items from it
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
class solve11 extends JFrame implements ItemListener, ActionListener {
 
    // frame
    static JFrame f;
 
    // label
    static JLabel l, l1;
 
    // combobox
    static JComboBox c1;
 
    // textfield to add and delete items
    static JTextField tf;
 
    // main class
    public static void main(String[] args)
    {
        // create a new frame
        f = new JFrame("frame");
 
        // create a object
        solve11 s = new solve11();
 
        // set layout of frame
        f.setLayout(new FlowLayout());
 
        // array of string containing cities
        String s1[] = { "Jalpaiguri", "Mumbai", "Noida", "Kolkata", "New Delhi" };
 
        // create checkbox
        c1 = new JComboBox(s1);
 
        // create textfield
        tf = new JTextField(16);
 
        // create add and remove buttons
        JButton b = new JButton("ADD");
        JButton b1 = new JButton("REMOVE");
 
        // add action listener
        b.addActionListener(s);
        b1.addActionListener(s);
 
        // add ItemListener
        c1.addItemListener(s);
 
        // create labels
        l = new JLabel("select your city ");
        l1 = new JLabel("Jalpaiguri selected");
 
        // set color of text
        l.setForeground(Color.red);
        l1.setForeground(Color.blue);
 
        // create a new panel
        JPanel p = new JPanel();
 
        p.add(l);
 
        // add combobox to panel
        p.add(c1);
 
        p.add(l1);
        p.add(tf);
        p.add(b);
        p.add(b1);
 
        f.setLayout(new FlowLayout());
 
        // add panel to frame
        f.add(p);
 
        // set the size of frame
        f.setSize(700, 200);
 
        f.show();
    }
    // if button is pressed
    public void actionPerformed(ActionEvent e)
    {
        String s = e.getActionCommand();
        if (s.equals("ADD")) {
            c1.addItem(tf.getText());
        }
        else {
            c1.removeItem(tf.getText());
        }
    }
 
    public void itemStateChanged(ItemEvent e)
    {
        // if the state combobox is changed
        if (e.getSource() == c1) {
 
            l1.setText(c1.getSelectedItem() + " selected");
        }
    }
}