Functional Interface in Java (With Real-World Examples) | Java 8 Feature

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In this tutorial, we dive into Functional Interfaces in Java, a key feature introduced in Java 8 that powers Lambda Expressions, Method References, and the Streams API.

Whether you're preparing for interviews or just getting started with modern Java programming, this video breaks down everything you need to know about Functional Interfaces — with crystal-clear explanations and real-world examples.

What You’ll Learn:
- What is an interface in Java (quick refresher)
- Why interfaces are important
- What is a Functional Interface (and why Java 8 introduced it)
- How to create and use Functional Interfaces
- @FunctionalInterface annotation – Do you need it?
- Real-world use cases using Lambda expressions, Streams, and custom interfaces
- Hands-on demo: Build a custom Functional Interface to perform math operations

Topics Covered (Timestamps):
00:00 - Introduction
00:14 - What is an Interface in Java?
02:13 - Why Do We Need Interfaces?
03:21 - What is a Functional Interface?
04:07 - How to Create a Functional Interface
05:34 - Understanding @FunctionalInterface Annotation
06:51 - Predefined Functional Interfaces
09:18 - Custom Functional Interface
12:42 - Summary

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