Objects Count so Count Objects!

One means to determine whether a student understands the fundamentals of good object-oriented design is to assess designs the student has created. However, providing reliable assessment of designs efficiently is difficult due to the many viable designs that are possible and the high level of expertise required. Consequently, design assessment tends to be limited to identifying the most basic of design problems. We propose a technique---"object counts''---that involves counting the objects created at runtime. This is more efficient than manual grading because the data is gathered automatically and more reliable than using rubrics because it is based on objective data. The data is relevant because it captures the fundamental property of an object-oriented program---the creation of objects---and so provides good insight into the student's design decisions. This provides support for both summative and formative feedback. We demonstrate the technique on two corpora containing submissions for a typical first assignment of an introductory course on object-oriented design.