JavaWiz

JavaWiz is a visualization plugin for Java programs targeted at programming beginners. Users can step through the program line by line and follow the execution in the visualization panel.

JavaWiz is developed and maintained by the Institute for System Software, Johannes Kepler University Linz, Austria.

Features

JavaWiz provides ten visualization views:

• Flow charts, visually representing the control flow of the program.
• A memory visualization. It displays statics, the stack, and the heap, to help understand how program memory works.
• A "tabular view" displaying the variable changes from line to line, which is useful for understanding simple algorithms.
• An array visualization showing index expressions, assignments, and the values in each array cell.
• A Linked List visualization showing nodes, references, and changes during list algorithms.
• A Binary Tree visualization showing tree structure and changes during tree algorithms.
• A Java Stream API visualization using dynamic Marble Diagrams to show execution order, transformations, intermediate results, and element lineage through the pipeline.
• Sequence diagrams, which show how objects relate to each other by depicting the method calls between them.
• Input buffer visualization
  • Hint: To use this feature, you have to use JavaWiz's In.java class to read input. This class can easily be added to your project by right-clicking on the project folder in the explorer and selecting "Create In.java".
• A History View for browsing calls and assignments across the complete execution trace, filtering or searching them, and jumping to matching program states.

How to use

The extension requires Visual Studio Code 1.87.0 or newer and at least JDK 25 to run.

Start

After installing JavaWiz from the VSCode marketplace and opening a .java file, the tool can be started by either:

• clicking Debug with JavaWiz above the main method, or
• right click into the opened editor and selecting Debug with JavaWiz from the context menu, or
• using the shortcut CTRL + SHIFT + J.

Navigation

An explanation of the user interface can be accessed by clicking on the Help button inside JavaWiz.

The arrow buttons in the toolbar navigate through the program, the yellow arrow restarts the program.

It is possible to step back and repeat parts of the program, i.e., there's no need to restart the program to re-inspect previous steps.

The current status (live or replay) is displayed in the toolbar.

The visualization tools (heap view, desk test, etc.) can be revealed using the selection buttons on the main view. To close a tool, press ❌. Some tools are customizable. Change their settings by pressing ⚙.

Code completion

For didactic reasons, certain code completion features can be activated and deactived using JavaWiz. For this, use the Disable Advanced Java Support and Enable Advanced Java Support context menu items in the editor.

Further information

Please note that the tool is targeted at beginners and is under active development, so not all language features of Java might be supported.

Icon sources:

• Desk test button: made by Darius Dan from www.flaticon.com
• Editor button: made by Becris from www.flaticon.com
• Stack button: made by hirschwolf from www.flaticon.com
• Heap button: made by Alfredo Hernandez from www.flaticon.com
• Wizard in help menu: made by Smashicons from www.flaticon.com
• Live/replay indicators: made by Google from www.flaticon.com
• Help button: made by Freepik from www.flaticon.com
• History button: history icon created by Konstantin Filatov - SVGrepo.com
• Linked list, tree, forwards/backwards, step over, reset button: made by SSW