Combo Box operation in Java Swing
In this section, you can learn how to operate the Combo
Box component, you will learn how to add items to the
combo box, remove items from the combo box.
This program shows a text field, a combo box and two
command buttons, first is for the adding items to the combo box and another is
for the removing items from the combo. When you click on the add command button
then the text of the text box is added to the combo box if the text box is not
blank otherwise a message box will display with the message "Please enter
text in Text Box". But when you click on the remove button the item at the
0th (zero) position of the combo box will be remove from the combo box if the
combo box has one item at least otherwise a message box will display with the
message "Item not available.". Following is the image for the result
of the given program:
This program has used various java APIs for doing
required are explained as follows:
JComboBox combo = new JComboBox(items);
The above code has been used to create a combo box in this program. The
JComboBox instance combo is created using the constructor of the JComboBox
class of the javax.swing.*; package. This constructor holds the string
array in which items for the combo box are kept.
getItemCount():
This is the method of the JComboBox class which return the number of the
items present is the combo box.
getItemAt(index):
this is the method of the JComboBox class which returns the name of the
item of the combo box at the specified position. This specification of position
the item in the combo box is held by the getItemAt() method as a parameter.
showMessageDialog():
This the method of the JOptionPane class of javax.swing.*;
package. This method displays some messages in the special dialog box. This
method holds two argument in this program in which first is the parent object
name and another is the message text which has to be displayed.
addItem(String):
This is the method of the JComboBox class which adds items to the combo
box. This method takes a string argument which is to be used to add to the combo
box.
removeItemAt(index):
This is the method of the JComboBox class which remove the item at the
specified position of the combo box. This method holds the integer value for the
position number of he of the item in combo box to remove it.
Here is the code of the program:
import javax.swing.*;
import java.awt.event.*;
public class AddRemoveItemFromCombo{
JComboBox combo;
JTextField txtBox;
public static void main(String[] args){
AddRemoveItemFromCombo ar = new AddRemoveItemFromCombo();
}
public AddRemoveItemFromCombo(){
JFrame frame = new JFrame("Add-Remove Item of a Combo Box");
String items[] = {"Java", "JSP", "PHP", "C", "C++"};
combo = new JComboBox(items);
JButton button1 = new JButton("Add");
txtBox = new JTextField(20);
button1.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
if (!txtBox.getText().equals("")){
int a = 0;
for(int i = 0; i < combo.getItemCount(); i++){
if(combo.getItemAt(i).equals(txtBox.getText())){
a = 1;
break;
}
}
if (a == 1)
JOptionPane.showMessageDialog(null,"Combo has already this item.");
else
combo.addItem(txtBox.getText());
}
else{
JOptionPane.showMessageDialog(null,"Please enter text in Text Box");
}
}
});
JButton button2 = new JButton("Remove");
button2.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
if (combo.getItemCount() > 0)
combo.removeItemAt(0);
else
JOptionPane.showMessageDialog(null,"Item not available");
}
});
JPanel panel = new JPanel();
JPanel panel1 = new JPanel();
panel.add(txtBox);
panel.add(combo);
panel.add(button1);
panel.add(button2);
frame.add(panel);
// frame.add(panel1);
frame.setSize(400, 400);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
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