General reminders

General reminders

To display a Swing component, you must:

• Construct and initialize the component.
  Example: button = new JButton ("ButtonLabel");
• Add it to the content pane of the window or to a JPanel that is added to the display, and validate the content pane after adding all components. For example to add a component to the south portion of the content pane of the window:

      Container contentPane = getContentPane();
      contentPane.add (button,BorderLayout.SOUTH);
      ...
      contentPane.validate();
  

  JPanels use FlowLayout, which does not allow a section of the screen to be specified, so the second parameter of the add method must be omitted when adding to a panel.

• Import javax.swing.* and often java.awt.* in the class creating the components.

To handle events from a GUI component, you must do the following:

• Declare that the class handling the event implements the appropriate listener interface.
  Example: implements ActionListener
• Define the method that the listener interface requires.
  Example: public void actionPerformed (ActionEvent event)
• Add a listener appropriate for the component to the component.
  Example: button.addActionListener (this);
• Import java.awt.event.* (and occasionally javax.swing.event.*) at the beginning of the class that is the listener.

When the listener method is called, you can find out which component sent the event by calling getSource() on the event.

    public void actionPerformed (ActionEvent event) {
        Object theButton = event.getSource();
        if (theButton == framedCircleButton) {
            // Create a framed circle
        }
    }

If a method returns a String or Object, remember to compare the result using the equals method, not ==. For example, aMenu.getSelectedItem ().equals ("A value")

General reminders