# A Modularity Bug in Java 8

## TL;DR

This paper identifies a modularity bug in Java 8's interface system, demonstrated through a vector space design example, highlighting the need for language extension to fix the compilation error.

## Contribution

It uncovers a specific modularity bug in Java 8's interface system using a practical example from teaching modular design.

## Key findings

- The bug causes a compilation error in Java 8.
- The bug affects modular object-oriented design.
- A language extension is proposed to fix the bug.

## Abstract

We demonstrate a modularity bug in the interface system of Java 8 on the practical example of a textbook design of a modular interface for vector spaces. Our example originates in our teaching of modular object-oriented design in Java 8 to undergraduate students, simply following standard programming practices and mathematical definitions. The bug shows up as a compilation error and should be fixed with a language extension due to the importance of best practices (design fidelity).