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11 GUI

Event

Change in the state of an object

generated by user’s interaction with the GUI (graphical user interface), such as

  • mouse movements
  • mouse clicks
  • pressing keys

Event Handling

control what happens if an event occurs

Delegation Event Model

UI and event logic are separate

Source

object on which event occurs

eg: buttons

Listener/Handler

object that

  1. waits for event to occur
  2. generates response for the event

eg: mouse click

listener should be registered with the source

Important events and listeners

  • java.util
  • java.awt
  • java.awt.event
Event Classes Interface Generated when
ActionEvent ActionListener - button press
- menu-item selected
- list-item is double clicked
MouseEvent MouseListener - mouse dragged, moved, pressed, released
- enter/exit a component
KeyEvent KeyListener keyboard input
ItemEvent ItemListener checkbox/list item is clicked
TextEvent TextListener textarea/textfield edited
MouseWheelEvent MouseWheelListener mousewheel moved
WindowEvent WindowListener window activated, deactivated, opened, closed
ComponentEvent ComponentEventListener component hidden
ContainerEvent ContainerListener
AdjustmentEvent AdjustmentListener
FocusEvent FocusListener

Swing

part of JFC(Java Foundation Classes)

import javax.swing

swing classes all start like J...

We are using Swing Library, cuz

  • Swing is for cross-platform applications; AWT is only for windows applications
  • Swing is ligher than AWT
graph TB
Object --> Component --> Container & JComponent

Container --> Window & Panel
Window --> JFrame & Dialog
Panel --> Applet

JComponent --> JLabel & JButton & x[many more...]
\[ \color{hotpink} \fbox{$ \underset{ \color{orange} \fbox{$ \underset{ \color{orange} \fbox{Components} }{Panel} $}} {\text{Frame}}$} \]

Containers

Top Level Lightweight
Weight heavy light
Dependence independent requires top level
eg JFrame, JDialog, JApplet JPanel

IDK

There are 2 ways

  1. instantiate JFrame class
  2. extend JFrame class
import java.awt.*;
import java.swing.*;

class GUI implements ActionListener
{
    GUI()
  {
    JFrame f = new JFrame();

    JLabel l = new JLabel("Blah Blah");

    JPanel p1 = new JPanel();
    JPanel p2 = new JPanel();

    JTextField tf = new JTextField();
    tf.setText("Blah");
    tf.setEditable(false);

    JButton btn = new JButton("Click me");
    btn.addActionListener(this);

    JCheckBox jc = new JCheckBox();
    jc.addActionListener(this);

    ButtonGroup bg = new ButtonGroup();
    JRadioButton r1 = new JRadioButton(),
        r2 = new JRadioButton(),
        r3 = new JRadioButton();
    bg.add(r1); bg.add(r2); bg.add(r3);

    p1.add(tf); p1.add(btn);
    p2.add(jc); p2.add(bg);

        f.add(p1); f.add(p1);
    f.add(l);

    f.setLayout(new FlowLayout() ); //null
    f.setSize(200, 400);
    f.setVisible(true);
  }

  public void actionPerformed(ActionEvent e)
  {
    JOptionPane.showMessageDialog(this, "message");
    if( e.getSource() == btn )
    {
      if( jc.isSelected() )
                ;
      if( r1.isSelected() )
        ;
      if( r2.isSelected() )
                ;
    }
  }
}
Last Updated: 2023-01-25 ; Contributors: AhmedThahir

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