Java JComboBox

Java JComboBox

JComboBox inherits from class JComponent.The selected choice pop-ups at the top of the menu.

How to declare JCombox

[public class JComboBox extends JComponent implements ItemSelectable, ListDataListener, ActionListener, Accessible]

JCombox constructors.

• JComboBox()-creates a combo box with default data model.
• JComboBox(Object [] items)-creates combo box that gets items from a specified array.
• JComboBox(Vector<?> items)-creates combo box with elements from a Vector

JCombox commonly used methods

• void addItem(Object object)-this method is used to add Item to the Item List.
• void removeItem(Object object)-used to remove item from Item List.
• void removeAllItems()-removes all items from the list.
• void setEditable(boolean )-if its set true,the JComboBox is editable.
• void addActionListener(ActionListener l)-adds actionListener 
• void addItemListener(ItemListener i)-adds ItemListener.

Java JComboBox Example

[

import javax.swing.JComboBox;
import javax.swing.JFrame;
public class JComboBoxExample extends JFrame {
    
    JComboBoxExample()
    {
    super("JComboBox Example");
    
    String languages []={"Java","C++","PHP","JavaScript","C#"};
    
    JComboBox box=new JComboBox(languages);
      box.setBounds(50, 50,90,20);    
            
    add(box);
    
     setSize(400,400);
   setLayout(null);
   setLocationRelativeTo(null);
  setDefaultCloseOperation(EXIT_ON_CLOSE);
  setVisible(true);
    
    }
    public static void main(String args[])
    {
         new JComboBoxExample();
    
    }
    
}

]

Java JComboBox with ActionListener Example

[

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.UIManager;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class JComboBoxExample extends JFrame implements ActionListener {
    public   JComboBox box;
    public JLabel label;
    public JButton button;

    JComboBoxExample()
    {
        super("JComboBox Example");
        try        {
            UIManager.setLookAndFeel
                    ("com.sun.java.swing.plaf.windows.WindowsClassicLookAndFeel");
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

        label = new JLabel();
        label.setHorizontalAlignment(JLabel.CENTER);
        label.setSize(400,100);
        add(label);
        String languages []={"Kenya","Somalia","Rwanda",
                "Tanzania","South Africa","Namibia","Nigeria"};

        box=new JComboBox(languages);
        box.setBounds(50,80,150,20);

        add(box);

        button=new JButton("Show");

        button.setBounds(50,150,100,30);
        add(button);
        button.addActionListener(this);

        setSize(400,400);
        setLayout(null);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);

    }
    public static void main(String args[])
    {
        new JComboBoxExample();

    }

    public void actionPerformed(ActionEvent event)
    {
        String lang="Country selected is  "+
                box.getItemAt(box.getSelectedIndex());
        label.setText(lang);
    }

}

]

Output:

Lessons you should learn from above program.

First you should note the difference between the two images.The look and Feel is different and this is courtesy of javax.swing.UIManager that i used to set WindowsClassicLookAndFeel using below code.

 [try

{
    UIManager.setLookAndFeel
            ("com.sun.java.swing.plaf.windows.WindowsClassicLookAndFeel");
}
catch(Exception e)
{
    e.printStackTrace();

}]

Above class extends and implements ActionListener.[public class JComboBoxExample extends JFrame implements ActionListener]What does this mean?

This means that class JComboBoxExample has access to all JFrame methods.These are:-

[

setSize(400,400);

setLayout(null);

setLocationRelativeTo(null);

setDefaultCloseOperation(EXIT_ON_CLOSE);

setVisible(true);

]

 setDefaultCloseOperation(EXIT_ON_CLOSE) is used to exit the application when the close button is clicked.

Implementing ActionListener interface means that you have to override public action performed method.

[

public void actionPerformed(ActionEvent event)
{
    String lang="Country selected is  "+
            box.getItemAt(box.getSelectedIndex());
    label.setText(lang);
}

]

Code to add  JComboBox to JFrame is  [ box.setBounds(50,80,150,20);].Read more about setBounds component method here

You may also consider setting ToolTipText to JButton or JComboBox

See also 

How to add ActionListener to JButton