Source

import java.applet.*;
import java.awt.*;

public class AnAppletWithLayout extends Applet {
	public void init() {
		setLayout(new BorderLayout());

		Button topButton = new Button("Top");
		add(topButton, BorderLayout.NORTH);

		Button bottomButton = new Button("Bottom");
		add(bottomButton, BorderLayout.SOUTH);

		Button rightButton = new Button("Right");
		add(rightButton, BorderLayout.EAST);

		Button leftButton = new Button("Left");
		add(leftButton, BorderLayout.WEST);

		Button middleButton = new Button("Middle");
		add(middleButton, BorderLayout.CENTER);
	}
}

Description and Objective

• Shows how to obtain better control over the positioning of the applet's interface components.

Notes

• Applets possess a default way in which components added to the applet are positioned
  • Left-to-right/top-to-bottom
• This behavior can be modified by specifying an alternative layout manager object for the applet.
  • The layout manager object is responsible for the positioning of the components on the applet's surface
  • Each layout manager provides a different way of positioning the components
  • The default layout manager for an applet is a FlowLayout object

• The BorderLayoutManager class provdes a layout consisting of five (5) regions
  • North - the upper portion of the surface
  • South - the lower portion of the surface
  • West - the left side of the surface
  • East - the right side of the surface
  • Center - the middle portion of the surface
• A slightly different form of the add method is used when working with BorderLayout
  • A second parameter is introduced specifying the desired region:

    add(button1, BorderLayout.NORTH);
    					

  • The BorderLayout class provides constants for the various regions
• The sizing of the laid out components when using BorderLayout takes some getting used to
  • Noth and South components are stretched for the entire width of the applet's surface
  • East and West components are stretched for the entire height between North and South
  • Center is stretched to fill in the entire middle
• Note that only 5 components can be placed when using BorderLayout

This Applet's Behavior

• The applet uses its setLayout method to change its layout manager to a BorderLayout object
• Five buttons are then placed in the five regions

Things to Do

• The BorderLayout class
  • What package is it in?
  • Find the region constants-- what are their types?
• Find the GridLayout class
  • What sort of layout does this class provide?