Functional Interface in Java 8 Explained | Lambda Expressions, @FunctionalInterface, Anonymous Class
Functional Interface in Java 8 is one of the most important concepts that enables Lambda Expressions and Functional Programming in Java.
In this video, we take a deep dive into Java Functional Interfaces, understand the rules of creating a functional interface, and learn how they form the foundation for Java 8 Lambda Expressions.
We start by understanding what a Functional Interface in Java 8 is and what makes an interface qualify as a functional interface. You’ll also learn the concept of an abstract method in Java, why a functional interface must contain only one abstract method, and how the @FunctionalInterface annotation helps enforce this rule.
Next, we explore why Functional Interfaces were introduced in Java 8 and how they enable functional programming in Java. The video clearly explains the evolution of interface implementations in Java — starting from creating child classes, then moving to inner classes and anonymous inner classes, and finally simplifying everything with lambda expressions.
You will also see multiple practical examples showing how Java Lambda Expressions reduce boilerplate code. We gradually move from simple to complex scenarios:
• Lambda expression when the abstract method has no parameters and no return type
• Lambda expression with single-line implementation
• Lambda expression with multiple parameters and return types
• Lambda expression with multiple lines of code
The video also explains an important concept: when a lambda expression is assigned to a functional interface reference, the implementation is stored in the object and executed only when the abstract method is invoked.
By the end of this tutorial, you will clearly understand functional interfaces, lambda expressions in Java 8, anonymous inner classes, and how Java supports functional programming concepts.
This video is perfect for Java developers, beginners learning Java 8 features, and developers preparing for Java interviews.
00:00 : Introduction
00:41 : Functional Interface
02:23 : @FunctionalInterface Annotation
03:57 : Lambda Expressions
14:33 : Lambda Expressions Example 1
16:25 : Lambda Expressions Example 2
17:38 : Lambda Expressions Example 3
21:48 : Lambda Expressions Example 4
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