Java Awt Components

From JavaProgramming

Overview of graphical components in JavaAwt. Simple examples of an application with a GraphicalUserInterface and a JavaApplet

Microsoft Windows API is based on Windows and graphical compo-nents on windows (buttons, text fields, etc.)
Java AWT (Abstract Window Toolkit) is 100% Object-Oriented. Meaning that all graphical components inherits from the same base classes
This goes for both GUI applications and Applets
A container is an area, which contains a number of components, i.e. a panel with buttons
A panel is a GUI area, which contains components or graphic drawing
An Applet is a specialisation of a panel, which can be con-tained within a website
A Frame is a window in a GUI application
A Frame can contain all components that inherit from class Component (that includes Applets see example of an Applet that can run as a GUI application later in this document)

Write a GUI application

Inherit from class Frame
Add an event listener for closing the application when receiv-ing a close event
Call Frame::setVisible() to make the window visible

  /* HelloWorldFrame.java */
  import java.awt.*;
  import java.awt.event.*;

  public class HelloWorldFrame extends Frame {
    public static void main(String[] args) {
      HelloWorldFrame frame = new HelloWorldFrame();
      Panel panel = new Panel();
      frame.add(panel);
      // Add event listener to close the application
      frame.addWindowListener(new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
          System.exit(0);
        }
      });
      frame.setTitle("HelloWorldFrame?");
      frame.setSize(400,320);
      // Call setVisible() to make the frame visible
      frame.setVisible(true);
      panel.getGraphics().drawString("Hello world!", 20, 20);
    }
  }

Write an Applet

Inherit from class Applet
Overwrite the method Applet::paint() to update graphics

  /* HelloWorldApplet.java */
  import java.awt.*;
  import java.applet.*;

  public class HelloWorldApplet extends Applet {
    public void paint(Graphics g) {
      g.drawString("Hello world!", 20, 20);
    }
  }

Show an Applet on a website

Compile the .java file to a .class file
Add tag <applet> to the .html file
Set the value code = the .class file
Set the value codebase = the path to the .class file relative to placement of the .html file
Set the values width and height to determine the size of the Applet

  /* HelloWorldApplet.html */
  <html>
  <head>
  <title>
  Test HelloWorldApplet
  </title>
  </head>
  <body>
  <applet
    code     = "HelloWorldApplet.class"
    codebase = "."
    width    = "400"
    height   = "300"
  >
  </applet>
  </body>
  </html>

Write an Applet that can run as a GUI application

Graphical components may be included in both GUI applications and Applets. The program below demonstrates this.

  /* StandAloneApplet.java */
  import java.awt.*;
  import java.awt.event.*;
  import java.applet.*;

  public class StandAloneApplet extends Applet {
    public void paint(Graphics g) {
      g.drawString("Hello world!", 20, 20);
    }
    public static void main(String[] args) {
      Frame frame = new Frame();
      StandAloneApplet applet = new StandAloneApplet();
      frame.add(applet);
      // Add event listener to close the application
      frame.addWindowListener(new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
          System.exit(0);
        }
      });
      frame.setTitle("Standalone Applet");
      frame.setSize(400,320);
      frame.setVisible(true);
    }
  }