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 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 */





code = "HelloWorldApplet.class"
codebase = "."
width = "400"
height = "300"
>

  
  
  

  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);
}
}