GUI:
The Graphical User
Interface

Dr Andy Evans

[Fullscreen]

Review

	
class A extends B {
	//Gets all public bits
}



class C implements D {
	// Fulfils promises
}
  • Methods that take a superclass will take the subclass, because they'll only use the superclass bits.

Inheritance

  • We can only extend one class, but we can implement many Interfaces using commas. 
    	
class A extends B implements C, D, E {

Example WIMP GUI

Windows, Icons, Mouse and Pointer.

The Graphical User Interface (GUI)

  • Nested objects subclassing java.awt.Component
    • e.g. a 'Window' object containing a 'JTree' containing 'Label' objects.
  • All have a 'Look and Feel'.
  • Two packages...
  • java.awt
    • Abstract Windows Toolkit: standard Look and Feel.
  • javax.swing
    • Part of the Java Foundation Classes (JFC): separates Look and Feel from components so you can let the JVM pick.

Major starting containers

Superclasses:
  • Component: Monitors keys/mouse and resizing.
  • Container: Uses 'LayoutManager' objects to position contents.
  • Window: Superclass for windows style objects : rarely used on own.
Classes actually used:
  • Panel and Canvas: A window with no border etc. Panel subclassed by Applet.
  • Frame: Window with border, close buttons and, potentially, menus.
  • JDesktopPanel: Used for making desktops.

Frame example

	
import java.awt.*;

public class PopUp {
    public PopUp() {
		Frame frame = 
			    new Frame("My Window");
		frame.setSize(300,300);
		frame.setVisible(true);
    }
    public static void main 
				(String args[]) {	
		new PopUp();
    }
}
  • You'll need Ctl-C to close it, or to shut the command window. Components do not usually respond to users automatically.
  • All measurements in pixels.

The life of a Frame

  • In your constructor create a Frame with a title. 
    	
Frame frame = new Frame ("My Window");
  • Set the size of the Frame. 
    	
frame.setSize(int width, int height);
frame.setSize(300,300);
  • Show the Frame. 
    	
frame.setVisible(true);  
		//Opposite is(false)

Adding other components

  • In the constructor make the other Components and add them to the Frame. 
    	
Label newLabel = new Label("My Label");
frame.add (newLabel);

The Alternative

  • To extend Frame and add functionality.
	
import java.awt.*;

class PopUp2 extends Frame {
    public PopUp2 () {
		super("My Window");
		setSize(300,300);
		Label newLabel = new Label("My Label");
		add (newLabel);
		setVisible(true);
    }
    public static void main (String args[]) {
		new PopUp2();
    }
}

Some useful components

Layout managers

  • Objects that control where components added to a container are displayed. 
    
LayoutManager layout = new LayoutManager();
guiObject.setLayout(layout);
  • Default for most is FlowLayout - as each component added they fill across the available space then wrap to the next line. Frame's BorderLayout allows you to add things to the CENTER/NORTH/SOUTH/EAST/WEST of the component.
  • Most of the rest are, frankly, pants.
  • The only one the pros use is GridBagLayout - this gives absolute positioning control, but allows for windows to resize.
  • We'll use FlowLayout and BorderLayout, but if you use GridBag you'll be ruler of the geeks. Lucky old you.

Summary

  • GUIs are made up of objects that subclass Component.
  • Some subclass Container, which in turn subclasses Component. These are usually the basis of a GUI.
  • You can make a Container, or extend it to add functionality
  • You can then make and add Components.
  • By default, none respond to user actions.