Why You Should Avoid Writing Thousand‑Line Classes and How to Refactor Them

When extending an existing project, the author discovered a class with 766 lines and nearly 40 public methods, which was painful to modify. To prevent such tragedies, the article emphasizes the importance of refactoring overly long classes.

Why Classes Should Not Be Too Long

Long classes are hard to read—scrolling through thousands of lines takes seconds, and even the original author may lose track of the logic. They are also hard to extend because many public interfaces make changes cumbersome.

Redundant code often inflates class size; duplicated code (produced by copy‑paste) leads to maintenance headaches, requiring changes in many places.

Excessive responsibilities violate the Single Responsibility Principle, causing divergent changes, divergent modifications, difficulty extending, and even triggering testing or operations failures.

Refactoring Strategies

Extract Redundant Code

Identify duplicated code and extract it into a separate method, reducing the original method’s length and centralizing future changes.

Change Method Signatures

Use IntelliJ IDEA’s refactor‑change‑signature feature (Ctrl+F6) to rename methods and adjust parameters, following a verb‑noun naming convention.

Move Fields and Methods

Select a field or method, right‑click → Refactor → Move, and transfer it to a more appropriate class, ensuring that the class that uses the member most frequently owns it.

Extract Class

When members cannot be moved to existing classes, create a new class to encapsulate related responsibilities. Use IDEA’s Extract → Delegate (or Parameter/Method Object) to delegate management of these members.

IDEA Workflow

Steps include locating duplicate code, using Refactor → Extract → Method (Ctrl+Alt+M), accepting signature changes, moving members, and extracting classes, with screenshots illustrating each action.

Finally, the article reminds readers that good refactoring principles apply across all technical domains.