🚫 Stop Writing Utility Classes the Old Way: Use Functional Interfaces Instead

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🧾 Introduction

Java developers often create utility classes like ValidationUtil, StringUtils, or DateUtil — full of static methods. These are quick to use but:

• Hard to test
• Impossible to swap at runtime
• Prone to becoming bloated

With Java 8 and beyond, there’s a better solution: functional interfaces and lambda expressions. This approach makes your code more flexible, testable, and modern.

In this article, you’ll see how to replace static utility classes with functional interfaces — using a complete, real-world working example.