Java FAQ: Top Questions

29. What are functional interfaces in Java?

A functional interface in Java is an interface with exactly one abstract method, used as a target for lambda expressions and method references. Introduced in Java 8, they enable functional programming.

@FunctionalInterface: Optional annotation to enforce one abstract method.
Standard Examples: Runnable , Predicate , Function , Consumer .
Custom Functional Interfaces: Define your own for specific lambda use cases.
Use with Streams: Often used in Stream API operations.

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