Java Swing | JComboBox with examples

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 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 contating 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 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 contating 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 Kolakata 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  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 contating 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"); 
        } 
    } 
} 

Output :

Note : the above programs might not run in an online compiler please use an offline IDE

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