How to use BiFunction functional interface in java 8 ?

BiFunction is a Functional interface with only one abstract method apply(T t, U u), which takes two arguments and return a result of type R. It is a generic interface defined as BiFunction<T, U, R>

BiFunction interfaces are typically implemented as lambda expressions.

import java.util.function.BiFunction;
import java.util.function.Function;

public class BiFunctionExample {
    public static void main(String[] args) {
        BiFunction<String, String, String> biFunction = (s1, s2) -> s1 + s2;
        System.out.println(checkStr(biFunction));
        Function<String, String> function = r -> "Result : " + r;
        System.out.println(biFunction.andThen(function).apply("b", "c"));
    }

    private static Boolean checkStr(BiFunction<String, String, String> biFunction) {
        if ("ab".equals(biFunction.apply("a", "b"))) {
            return true;
        }
        return false;
    }
}

Result:

true
Result : bc