Why Long Classes Are Problematic and How to Refactor Them

Promise me, no more thousand‑line classes

When extending an existing project I encountered a class of 766 lines with nearly 40 public methods, which I had to refactor with great difficulty.

This post highlights the importance of code refactoring to avoid such tragedies.

Why classes should not be overly long

Unreadable and hard to extend

Reading a long class takes several seconds of scrolling, making it hard even for the original author to understand.

Too many public interfaces make extensions cumbersome, often requiring changes across thousands of lines.

Redundant code

Redundant code—usually copy‑pasted—bloats methods and classes and forces scattered modifications.

Redundant code makes methods and classes long and non‑concise.

Every copy‑paste location must be updated when the logic changes.

Excessive responsibilities

A class exposing dozens of interfaces almost certainly violates the Single Responsibility Principle, leading to divergent changes, divergent modifications, and difficulty in extension.

Key problems include:

Violation of SRP : a class should implement only one responsibility.

Divergent changes : many callers cause the class to change frequently.

Divergent modifications : many dependent components must be updated together.

Hard to extend : subclasses or wrappers must implement numerous methods.

Testing and operations pain : more code means more potential failures.

What to do if you already have thousands of lines

Refactor – Extract redundant code

Identify duplicate code and extract it into a separate method, reducing repetition and centralising future changes.

IDEA steps:

Find duplicate code.

Use Ctrl + Alt + m (or Refactor → Extract → Method) to extract the method.

Adjust the method signature with Ctrl + F6 if needed.

Refactor – Move fields and methods (transfer responsibilities)

Move members that do not belong to the class to a more appropriate class.

IDEA steps:

Select the field, right‑click → Refactor → Move, then choose the target class.

Repeat the same for methods.

Refactor – Extract a new class

When no existing class can take the responsibilities, create a new class to hold the extracted fields and methods.

IDEA steps:

Select members, Refactor → Extract → Delegate (or Parameter Object / Method Object if appropriate).

Name the new class and choose its package.

Ensure the extracted members are used more often by the new class than by the remaining code (cohesion principle).

By following these techniques, long, tangled classes can be broken down into cohesive, single‑purpose components, improving readability, maintainability, and extensibility.