Java Swing - GUIs
TOPIC 03 – MORE ON COMPONENTS

LESSON NOTE - JCHECKBOX

JCHECKBOX CONSTRUCTOR

We create a JCheckBox by specifying the text associated with the checkbox.

JCheckBox cb = new JCheckBox("hello");

After adding the JCheckBox to the content pane, we get this:

SELECTED?

To know the state of the checkbox, we use the isSelected() method. It returns either true or false.

boolean state = cb.isSelected();

SETTING THE STATE

To set the state of the checkbox to either selected or not selected, we use the setSelected(boolean) method.

cb.setSelected(true);

ACTION LISTENER

We can add an action listener to the JCheckBox. After we do so, an event is triggered whenever the checkbox is clicked on.

ACTIONPERFORMED METHOD

To respond to an event, we check the source of the event. If the event comes from the JCheckBox, then we get the selected text or index.

public void actionPerformed(ActionEvent e)

{

if (e.getSource() == cb)

{

System.out.println("Selected? " + cb.isSelected());

}

}

FULL CODE EXAMPLE

Here is a complete example that shows the concepts from above in action.

public class MyGUI extends JFrame implements ActionListener

{

//datafields

JCheckBox cb;

public MyGUI()

{

Container cp = this.getContentPane();

cp.setLayout(new FlowLayout());

cb = new JCheckBox("hello");

cb.setSelected(true); //starting state

cb.addActionListener(this);

cp.add(cb);

this.setTitle("JCheckBox");

this.pack();

this.setVisible(true);

}

public void actionPerformed(ActionEvent e)

{

if (e.getSource() == cb)

{

System.out.println("Selected? " + cb.isSelected());

}

}

public static void main(String[] args)

{

MyGUI sg = new MyGUI();

}

}