Exploring Modular Programming in Java with Project Jigsaw

Introduction: Why Modular Programming Matters.

When I started working on large-scale Java applications, I quickly realized the monolithic JAR problem: everything bundled together, dependencies leaking everywhere, and no clear boundaries between modules. With Java 9, Project Jigsaw finally introduced a module system to solve this.

This article is my practical experience with modular programming in Java using Project Jigsaw — what it is, how it works, and how I’ve structured real-world projects with it.

1. The Problem with Monolithic JARs

Before Jigsaw, Java had only packages and JARs. The issues:

• No true encapsulation (all public classes accessible).
• Dependency hell (classpath conflicts, versioning issues).
• Hard to scale large projects into clean, independent modules.

Developers often used tools like OSGi, but nothing native existed until Java 9.

2. Enter Project Jigsaw and the Java Platform Module System (JPMS)

Jigsaw introduced:

• module-info.java descriptor file.