Visually Introducing Freshmen to Low-Level Java Abstractions for Creating, Synchronizing and Coordinating Threads

We have developed and experimented with an approach to teach low-level Java concurrency abstractions in our first required course for CS majors, which assumes knowledge of procedural programming. The driving problems are visualized simulations of multiple physical objects in motion that may (a) be confined to a shared space and (b) coordinate with each other. Such simulations do not require any domain-specific knowledge such as sorting and image processing for driving problems and exercises, and their implementation demonstrates the benefits of object-based programming. They allow focus on both the performance and programmability benefits of concurrency, provide analogies for an abstraction-independent explanation of concurrency concepts, and can be used to incrementally motivate all low-level concurrency abstractions and visualize the effect of using and not using these abstractions. Layered simulation-based worked examples illustrating the abstractions were presented and easily understood in multiple offerings of a course that implemented this approach. Students implemented non-trivial assignments based on these abstractions, even when they were optional, did not face major obstacles because of visual error feedback, and were excited by concurrency as they felt it empowered them to implement arbitrary applications early.