Simple usage of Lambda expression with an in-class defined functional interface

LambdaCalculator.java

package lambdaCalculator;

/**
 *
 * @author @ectomorph
 */
public class LambdaCalculator {
    
    // In-class defined interface
    @FunctionalInterface
    interface IntegerMath {
        int operation(int a, int b);
    }

    public int binaryOperator(int a, int b, IntegerMath op) {
        return op.operation(a, b);
    }

    public static void main(String... args) {

        LambdaCalculator myCalc = new LambdaCalculator();
        
        System.out.println("10 * 10 = " + myCalc.binaryOperator(10, 10, (a, b) -> a * b));

        // or, how about this? Using an in-class defined functional interface
        IntegerMath addition = (a, b) -> a + b;
        IntegerMath subtraction = (a, b) -> a - b;
        
        System.out.println("40 + 2 = " + myCalc.binaryOperator(40, 2, addition));
        System.out.println("20 - 10 = " + myCalc.binaryOperator(20, 10, subtraction));        
    }
}