Computational Problem Solving with Java and Interactive Object Graphics

DoodlePad is an open source object oriented graphics library that is designed to help you learn Java in a fun and engaging manner. It automatically sets up the Java graphics program infrastructure for you, including graphic object management, rendering, double buffering and a diverse set of pixel-perfect, shape-specific events and event handling. DoodlePad is ideal for introductory computing education because it lets you focus on developing core programming skills using interactive computer graphics without the need to learn the details of a Java windows toolkit, computer graphics, and the event system. DoodlePad is designed to help you get started quickly and to have a Java graphics program running in no time.

From a user’s perspective, DoodlePad is nothing more than a zip archive file containing precompiled Java classes ready for use, and packaged as a Java Archive (JAR) file. No installation is required other than to download the doodlepad.jar file from the project’s GitHub repository¹. You will find a direct link to the GitHub repository and the JAR file at the site https://doodlepad.org/².

While developing the DoodlePad library, care has been taken to ensure that the library works across process boundaries. This allows us to use DoodlePad interactively from tools like JShell. As a preview, below you’ll find a JShell session that creates a default Oval object in a graphics window. The result of executing these commands will be similar to the Window that follows. After downloading the doodlepad.jar file and saving to your working folder, make sure to tell Java where to find the file using the /env --class-path doodlepad.jar command, and to import all classes into JShell using the import doodlepad.*; command. Creating the new Oval object is as simple as executing the command new Oval();.

This simple script demonstrates how DoodlePad allows a programmer to focus on writing their program, such as the creation of an Oval object, and not on details such as creating all the ancilliary AWT and Swing infrastructure, such as the JFrame and JPanel objects, as well as how to use a Graphics2D object, etc.

>jshell
|  Welcome to JShell -- Version 17.0.6
|  For an introduction type: /help intro

jshell> /env --class-path doodlepad.jar
|  Setting new options and restoring state.

jshell> import doodlepad.*;

jshell> new Oval()
$2 ==> Oval x=61.94595675351811, y=130.01502432069648, width=100.0, height=100.0, layer=doodlepad.Layer@47ef968d

jshell>

Figure 1.9.2 is a small gallery of random DoodlePad graphic objects. We will begin using DoodlePad library classes in Section 14.1