B. To provide a callback mechanism for lambda expressions. Explanation: Functional interfaces, introduced in Java 8, play a crucial role in enabling functional programming paradigms within the object-oriented framework of Java. They achieve this by: Single Abstract Method (SAM): Functional interfaces can have only one abstract method. This single method signature acts as a blueprint for anonymous functions or lambda expressions. Lambda expressions can be used as arguments to methods or passed to higher-order functions, providing concise and flexible ways to define behavior. For example: Java @FunctionalInterface // Optional annotation for clarity public interface StringProcessor { String process(String str); } String result = processString("Hello", str -> str.toUpperCase()); // Lambda expression used as argument private String processString(String str, StringProcessor processor) { return processor.process(str); // Functional interface used for callback } Incorrect statements and explanations: A. Functional interfaces are not specifically designed to define static helper methods. While they can potentially hold static methods, their main focus is defining a single abstract method for lambda expressions C. Functional interfaces don't enforce specific naming conventions for methods. The method name and signature define the behavior expected from the implementing class or lambda expression. D. Functional interfaces primarily deal with method functionality, not access restriction. The visibility of methods within an interface is usually public or protected, depending on the design.
