Java GUI

Java GUI

Desktop GUI applications

AWT(Abstract Window Toolkit)
Swing(Java Foundation Classes)
- Pluggable Look and Feel
- Platform Independent components
- Enhanced component library

Swing v.s. AWT

AWT is a Java interface to native system GUI code present in your OS. It will not work the same on every system, although it tries.
Swing is a more-or-less pure-Java GUI. It uses AWT to create an operating system window and then paints everything else on it.
Thus Swing is 100% portable and is the same across platforms.

AWT Packages

java.awt
- GUI container classes
  - Frame
  - Panel
  - Dialog
  - ScrollPane
- GUI component classes
  - Button
  - TextField
  - Label
- Layout managers
  - BorderLayout (Positions), default for Frame
  - FlowLayout (Alignments), default for Panel / Applet
  - GridLayout
  - CardLayout, add panels/cards one behind the other
  - NullLayout, custom
- Custom graphics classes
  - Graphics
  - Color
  - Font
java.awt.event
- Event classes
  - ActionEvent
  - MouseEvent
  - KeyEvent
  - WindowEvent
- Event listener interfaces
  - ActionListener
  - MouseListener
  - KeyListener
  - WindowListener
- Event listener adapter classes
  - MouseAdapter
  - KeyAdapter
  - WindowAdapter

Container

Top Lever Containers

Frame
Dialog
Applet

Secondary Containers

Panel
ScrollPane

Frame

By default, frame’s size is (0,0) and visibility is false;

f = new Frame();
f.setSize(500, 500);
f.setVisible(true);

Event Handing

Component (source/listener object)
- Button
- Label
- List
- Checkbox
- Choice
- TextField
Event
Listener

Work Flow

create Source Object (e.g. create a button)
create Listener Object (e.g. implement listener interface, override actionperformed method)
register Listener to Source (e.g. button.addActionListener(l))
wait for user to trigger the ActionListener -> (e.g. button create a new Event and invoke the actionperformend mehtod of the Lister Object)

java_awt_flow

notice: Listener interfaces are abstract, must override all methods; to avoid using interface, we can use(extends) the adapter (class)

Example

code source from https://www3.ntu.edu.sg/home/ehchua/programming/java/J4a_GUI.html

import java.awt.*;       // Using AWT layouts
import java.awt.event.*; // Using AWT event classes and listener interfaces
import javax.swing.*;    // Using Swing components and containers

// A Swing GUI application inherits from top-level container javax.swing.JFrame
public class SwingCounter extends JFrame {   // JFrame instead of Frame
   private JTextField tfCount;  // Use Swing's JTextField instead of AWT's TextField
   private JButton btnCount;    // Using Swing's JButton instead of AWT's Button
   private int count = 0;
 
   // Constructor to setup the GUI components and event handlers
   public SwingCounter () {
      // Retrieve the content-pane of the top-level container JFrame
      // All operations done on the content-pane
      Container cp = getContentPane();
      cp.setLayout(new FlowLayout());
 
      cp.add(new JLabel("Counter"));
      tfCount = new JTextField("0", 10);
      tfCount.setEditable(false);
      cp.add(tfCount);
 
      btnCount = new JButton("Count");
      cp.add(btnCount);
 
      btnCount.addActionListener(new ActionListener() {
         @Override
         public void actionPerformed(ActionEvent evt) {
            ++count;
            tfCount.setText(count + "");
         }
      });
 
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setTitle("Swing Counter");
      setSize(300, 100);
      setVisible(true);
   }
 
   public static void main(String[] args) {
      // Run the GUI construction in the Event-Dispatching thread for thread-safety
      SwingUtilities.invokeLater(new Runnable() {
         @Override
         public void run() {
            new SwingCounter(); // Let the constructor do the job
         }
      });
   }
}