Have you created interfaces in your practice based on functional programming style?

Yes, in Java it is possible to create interfaces that use a functional programming style, especially with the introduction of lambda expressions and functional interfaces in Java 8.

A functional interface is an interface with a single abstract method, which can be implemented using a lambda expression or a method reference.

Example of a functional interface:

@FunctionalInterface
public interface Calculator {
    int calculate(int a, int b);
}

// Usage with a lambda expression
Calculator sum = (a, b) -> a + b;
int result = sum.calculate(5, 3); // 8

This approach allows writing more concise and expressive code, facilitates passing behavior as parameters, and promotes a programming style close to functional programming.