java clean code examples

import java.util.Arrays; import java.util.List; import java.util.function.BinaryOperator;

public class Duplication { public static void main(String[] args) { List numbers = Arrays.asList(1, 2, 3, 4, 5); Integer product = Math2.sum(numbers); System.out.println(product); } }

//with duplication class Math1 { public static Integer sum(List numbers) { Integer sum = 0; for (Integer n : numbers) { sum += n; } return sum; }

public static Integer multiply(List<Integer> numbers) {
    Integer product = 1;
    for (Integer n : numbers) {
        product *= n;
    }
    return product;
}

}

//after refactor with lambda class Math2 {

public static Integer reduce(List<Integer> numbers, Integer unit, BinaryOperator<Integer> operator) {
    Integer result = unit;
    for (Integer n : numbers) {
        result = operator.apply(result, n);
    }
    return result;
}

public static Integer sum(List<Integer> numbers) {
    return reduce(numbers, 0, (x, y) -> x + y);
}

public static Integer multiply(List<Integer> numbers) {
    return reduce(numbers, 1, (x, y) -> x * y);
}

}