A Short Introduction to the Lightweight Java Visualizer

Lightweight Java Visualizer – LJV

A short introduction for AP Computer Science* teachers

LJV has many uses for the AP Computer Science teacher.

A tool students can use to visualize what their programs are doing.
To quickly create images to use in presentations (e.g., Power Point) and handouts.
To better understand Java collection classes without having to wade through the source code (or as an aid to following the source code.)

LJV can help students to visualize relationships

A Triangle object containing LineSegments each containing Point objects.

LJV is so EASY to use! Click on any image to see the source code that created it.

Just as easily LJV can help students to better understand arrays.

An array with four numbers.

A five element array with 3 references to Point objects.

Same five element array with a different look (requires two extra lines of code.)

LJV can take some of the mystery out of Java collections classes.

An ArrayList with references to 5 Point objects.

Students can experiment – what happens to this ArrayList after an 11^th Point is added? LJV calls can be inserted at several points in a program, creating a sequence of images that can show insertions, deletions, etc.

Imagine drawing the following HashMap example on the board!

Students can use LJV to see their own data structures – implementations of Queue, Stacks, and PriorityQueues, as well as structures using TreeNodes and ListNodes.

Source code: Point.java and LineSegment.java

Let's get started!

Download GraphViz here. This is the program that actually produces the image files. Windows, Linux, and Mac installations are available.
Download LJV.java here, compile it and make it available to your project.
Try out the LJV tutorial.

* AP and Advanced Placement Program are registered trademarks of the College Entrance Examination Board which was not involved in the production of this Web site.