Computational Problem Solving with Java and Interactive Object Graphics

This book was born from materials developed to teach many sections of the course CSC 220: Computational Problem Solving at The College of New Jersey⁷. Rather than start with the Java compiler, this book introduces students to the interactive Java Shell named with which we explore primitive types, basic objects, and expressions, interactively. We avoid starting with the magical public static void main(String[] args) {… in favor of core topics such as types and memory. The Java compiler and runtime is deferred until Your First Java Program.

This book also introduces the learning library for Java called DoodlePad. DoodlePad is an open-source, interactive object graphics library for Java which was developed expressly to teach computing in a fun and engaging context. The DoodlePad library provides introductory students with the ability to create Java AWT/Swing applications and to render basic graphic objects without the need to master advanced Java concepts (like interface implementation and method overriding) required for using Swing and the AWT. DoodlePad works by bootstrapping the Swing intrastructure automatically, as necessary to create a graphics Window and to draw shapes. It also implements a pixel-prefect event dispatch system, which allows introductory students to interact with shapes using the mouse. The event system uses method references, introduced Java 8, to assign custom, student-authored methods as individual event handlers.

Note that JShell and DoodlePad may be used together. For example, the following interactive JShell session containing three lines is all that is necessary for the student to create their first Java AWT/Swing Program with an interactive Oval displayed. This gives students the ability to get running very quickly, on the first day. It builds confidence and dispels the real fear felt by so many introductory programming students entering a Java class for the first time.

jshell> /env -c doodlepad.jar
jshell> import doodlepad.*;
jshell> new Oval()

DoodlePad was designed conservatively. All user-initiated graphics commands are first checked to see if they are being invoked on a thread different than the main AWT event-dispatching thread. If so, it uses SwingUtils.invokeLater() to invoke the user-initiated command to ensure that the command is added to the AWT event-dispatching thread. This makes it possible for student programs to interact with Swing programs seamlessly. It also makes the interactive nature of invoking graphics programs from JShell work without a hitch. While crossing thread boundaries does incur a performance penalty, it shelters introductory students from the complexities of cross-thread programming and achieves one of the libraries main goals, which is for a program to "just work."

An advantage of self-publishing a book online is that corrections, clarifications, and additions may be made immediately. There is no need to wait for the next edition. If you find any problems with this book, or would like to make suggestions, please send an email to the author.

Enjoy!