Container in Java Swing Example

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:

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

Commonly used Methods are :

1. addItem(E item) : adds the item to the JComboBox
2. addItemListener( ItemListener l) : adds a ItemListener to JComboBox
3. getItemAt(int i) : returns the item at index i
4. getItemCount(): returns the number of items from the list
5. getSelectedItem() : returns the item which is selected
6. removeItemAt(int i) : removes the element at index i
7. 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.
8. setSelectedIndex(int i): selects the element of JComboBox at index i.
9. showPopup() :causes the combo box to display its popup window.
10. setUI(ComboBoxUI ui): sets the L&F object that renders this component.
11. setSelectedItem(Object a): sets the selected item in the combo box display area to the object in the argument.
12. setSelectedIndex(int a): selects the item at index anIndex.
13. setPopupVisible(boolean v): sets the visibility of the popup.
14. setModel(ComboBoxModel a) : sets the data model that the JComboBox uses to obtain the list of items.
15. setMaximumRowCount(int count): sets the maximum number of rows the JComboBox displays.
16. setEnabled(boolean b): enables the combo box so that items can be selected.
17. removeItem(Object anObject) : removes an item from the item list.
18. removeAllItems(): removes all items from the item list.
19. removeActionListener(ActionListener l): removes an ActionListener.
20. isPopupVisible() : determines the visibility of the popup.
21. addPopupMenuListener(PopupMenuListener l) : adds a PopupMenu listener which will listen to notification messages from the popup portion of the combo box.
22. getActionCommand() : returns the action command that is included in the event sent to action listeners.
23. getEditor(): returns the editor used to paint and edit the selected item in the JComboBox field.
24. getItemCount() : returns the number of items in the list.
25. getItemListeners(): returns an array of all the ItemListeners added to this JComboBox with addItemListener().
26. createDefaultKeySelectionManager() : returns an instance of the default key-selection manager.
27. fireItemStateChanged(ItemEvent e) : notifies all listeners that have registered interest for notification on this event type.
28. firePopupMenuCanceled() : notifies PopupMenuListeners that the popup portion of the combo box has been canceled.
29. firePopupMenuWillBecomeInvisible() : notifies PopupMenuListeners that the popup portion of the combo box has become invisible.
30. firePopupMenuWillBecomeVisible() : notifies PopupMenuListeners that the popup portion of the combo box will become visible.
31. setEditor(ComboBoxEditor a): sets the editor used to paint and edit the selected item in the JComboBox field.
32. setActionCommand(String a) : sets the action command that should be included in the event sent to actionListeners.
33. getUI() : returns the look and feel object that renders this component.
34. paramString() : returns a string representation of this JComboBox.
35. getUIClassID() : returns the name of the Look and feel class that renders this component.
36. 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

import java.awt.event.*;

import java.awt.*;

import javax.swing.*;

class solve extends JFrame implements ItemListener {

static JFrame f;

static JLabel l, l1;

static JComboBox c1;

public static void main(String[] args)

{

f = new JFrame( "frame" );

solve s = new solve();

f.setLayout( new FlowLayout());

String s1[] = { "Jalpaiguri" , "Mumbai" , "Noida" , "Kolkata" , "New Delhi" };

c1 = new JComboBox(s1);

c1.addItemListener(s);

l = new JLabel( "select your city " );

l1 = new JLabel( "Jalpaiguri selected" );

l.setForeground(Color.red);

l1.setForeground(Color.blue);

JPanel p = new JPanel();

p.add(l);

p.add(c1);

p.add(l1);

f.add(p);

f.setSize( 400 , 300 );

f.show();

}

public void itemStateChanged(ItemEvent e)

{

if (e.getSource() == c1) {

l1.setText(c1.getSelectedItem() + " selected" );

}

}

}

Output :

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

Java

import java.awt.event.*;

import java.awt.*;

import javax.swing.*;

class solve extends JFrame implements ItemListener {

static JFrame f;

static JLabel l, l1, l3, l4;

static JComboBox c1, c2;

public static void main(String[] args)

{

f = new JFrame( "frame" );

solve s = new solve();

String s1[] = { "Jalpaiguri" , "Mumbai" , "Noida" , "Kolkata" , "New Delhi" };

String s2[] = { "male" , "female" , "others" };

c1 = new JComboBox(s1);

c2 = new JComboBox(s2);

c1.setSelectedIndex( 3 );

c2.setSelectedIndex( 0 );

c1.addItemListener(s);

c2.addItemListener(s);

c1.setEditable( true );

l = new JLabel( "select your city " );

l1 = new JLabel( "Jalpaiguri selected" );

l3 = new JLabel( "select your gender " );

l4 = new JLabel( "Male selected" );

l.setForeground(Color.red);

l1.setForeground(Color.blue);

l3.setForeground(Color.red);

l4.setForeground(Color.blue);

JPanel p = new JPanel();

p.add(l);

p.add(c1);

p.add(l1);

p.add(l3);

p.add(c2);

p.add(l4);

p.setLayout( new FlowLayout());

f.add(p);

f.setSize( 400 , 400 );

f.show();

}

public void itemStateChanged(ItemEvent e)

{

if (e.getSource() == c1) {

l1.setText(c1.getSelectedItem() + " selected" );

}

else

l4.setText(c2.getSelectedItem() + " selected" );

}

}

Output :

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

Java

import java.awt.event.*;

import java.awt.*;

import javax.swing.*;

class solve11 extends JFrame implements ItemListener, ActionListener {

static JFrame f;

static JLabel l, l1;

static JComboBox c1;

static JTextField tf;

public static void main(String[] args)

{

f = new JFrame( "frame" );

solve11 s = new solve11();

f.setLayout( new FlowLayout());

String s1[] = { "Jalpaiguri" , "Mumbai" , "Noida" , "Kolkata" , "New Delhi" };

c1 = new JComboBox(s1);

tf = new JTextField( 16 );

JButton b = new JButton( "ADD" );

JButton b1 = new JButton( "REMOVE" );

b.addActionListener(s);

b1.addActionListener(s);

c1.addItemListener(s);

l = new JLabel( "select your city " );

l1 = new JLabel( "Jalpaiguri selected" );

l.setForeground(Color.red);

l1.setForeground(Color.blue);

JPanel p = new JPanel();

p.add(l);

p.add(c1);

p.add(l1);

p.add(tf);

p.add(b);

p.add(b1);

f.setLayout( new FlowLayout());

f.add(p);

f.setSize( 700 , 200 );

f.show();

}

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 (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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Source: https://www.geeksforgeeks.org/java-swing-jcombobox-examples/

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