Why Long Classes Break Your Code and How to Refactor Them with IDEA

Why Classes Shouldn't Be Too Long

Classes that grow to hundreds of lines and expose dozens of public methods become unreadable and difficult to extend, causing developers to waste time scrolling and understanding the code.

Long Classes May Contain Redundant Code

Redundant code, often created by copy‑paste, makes methods and classes overly long, leads to scattered changes, and increases maintenance effort.

Long Classes Usually Have Too Many Responsibilities

When a class has many interfaces it violates the Single Responsibility Principle, resulting in divergent changes, divergent modifications, and hard‑to‑extend designs.

If you know someone with a class over a thousand lines, share this article with them.

What to Do When Your Class Has Thousands of Lines?

Refactor: Extract Redundant Code

Identify duplicate code and extract it into a separate method, replacing the copies with a single method call, which shortens the original method and centralizes future changes.

Extract Redundant Code with IDEA

1. Find duplicate code

2. Extract method (Right‑click → Refactor → Extract → Method or Ctrl+Alt+M)

IDEA can detect slight variations and suggest accepting signature changes to replace more occurrences.

3. Change method signature (Ctrl+F6)

Use verb‑noun naming for methods, e.g., clean() instead of cleanWithBrush() .

Refactor: Move Fields and Methods (Transfer Responsibility)

Move fields and methods that belong to another class by right‑clicking → Refactor → Move, selecting the appropriate target class.

Refactor: Extract Class

If no existing class can take the moved members, create a new class to hold them. Use Refactor → Extract → Delegate to create a delegate, parameter object, or method object as appropriate.

When naming the new class, ensure the extracted functions use the moved fields more often than the remaining functions to respect the cohesion principle.

Do not extract parameter objects unless they are needed for methods with many parameters.