Class 17: Java's Abstract Windowing Toolkit

Held Thursday, September 23, 1999

Overview

Today, you will continue your investigation of graphical programs that use Java's Abstract Windowing Toolkit. In particular, you will build event-driven programs that include buttons and text fields.

Notes

• There's still time to sign up for the picnic. The sign-up sheet is next to my door.
• The ACM Chapter meeting will be Sunday at 2:00 in the room next to the MathLAN. Contact Joey Lesh ( lesh@grinnell.edu) for more information.
• You've been assigned teams and subprojects. For next Wednesday, each team should prepare a summary of the objects they plan to create and the methods they will support.
  • The GUI groups should also have sketches of their interfaces.
• Any final questions on exam 1?
  • A few of you have asked how you might find the errors in problem C. One possibility is to print out a message at each step to tell what's happening.
  • Some of you have asked me how you might convert Strings to doubles (although I'm not sure why). As we've discussed in the past, you should use something like

         double d = (new Double(___)).doubleValue();
    

    or

         Double bigD = new Double(___);
         double d = bigD.doubleValue();
    

  • No, you do not have to write code for question 2. You should, however, identify all the parameters of all your methods.
• Once again, we'll focus on the lab, with a short time for reflection and summarization.

Contents

• Lab
• GUIs in Java

Handouts

• Lab G2: Java's AWT
• List of project teams

Summary

• Graphical User Interfaces
  • The event-driven model
  • Using components
• Lab: G2
• Assignments:
  • Read G3 for tomorrow.
  • For next Wednesday, develop an initial interface for all the classes you expect to include in your component of the project. Turn in compilable files. GUI teams should also sketch the windows they expect to show.

Lab

Do as much of G2.1 through G2.4 as you can. (You should finish up the rest in the evening.)

GUIs in Java

• Although many of the programs we've been writing are text-based, most modern programs use a graphical user interface (GUI).
• Java's included toolkits for building GUIs since the early versions.
  • Unfortunately, these toolkits have changed substantially as Java evolved from 1.0 to 1.1 and from 1.1 to 1.2.
  • We'll focus on the Abstract Windowing Toolkit (awt) as it is supported in Java 1.1 and Java 1.2.
  • Java 1.2 add Swing, but Swing is not yet fully supported on our HP/UX workstations.
• GUIs use an event-driven programming model. We might also call this a reactive model.
  • Rather than using an imperative model in which your program says step-by-step what do do, reactive programs have event handlers which basically say ``when this happens, do this''.
  • You'll still need a main method to create the objects which supply these event handlers.
• As you might guess, GUIs have a number of components (menus, buttons, labels, etc.). In Java, each component is an object.
• We put components into windows and frames using the add method.
• Each component can have one or more listeners that respond to the events that pertain to the object. (You should have read something about this in chapter 1 of Java Plus Data Structures.)
• The rest of the details are in the lab.