Java Design Tips That Save You From Future Pain

Simple Practices for Cleaner Java Code

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Writing Java that just works is easy.
Writing Java that’s clean, scalable, and maintainable - that’s what separates good developers from great ones.

In this post, you’ll find some practical code design best practices that every Java developer should follow, explained clearly with examples, common mistakes, and the right way to do it.

1) Favor Composition over Inheritance

Use composition (has-a) rather than inheritance (is-a) unless the relationship is truly hierarchical and behavior needs to be shared.

Why It Matters:

• Inheritance tightly couples classes and makes code rigid.
• Composition allows greater flexibility and testability.
• Changes in the base class can unintentionally break subclasses.

Common Bad Usage:

class Engine { ... }
class Car extends Engine { ... }  // BAD — Car is not an Engine!

Better Way:

class Car {
    private Engine engine;
}

This way, Car uses Engine, but isn’t forced to inherit all its behavior. You can now swap engines (like…