Sample.java

import java.util.*;
import java.util.function.Predicate;
public class Sample {
  public static int totalValues(List<Integer> values, Predicate<Integer> selector) {
    // int result = 0;
    // for(int e: values) {
    //   if(selector.test(e))
    //     result += e;
    // }
    // return result;
    // return values.stream()
    //              .filter(selector)
    //              .reduce(0, Integer::sum);
    return values.stream()
                 .filter(selector)
                 .mapToInt(e -> e)
                 .sum();
  }
  public static void main(String args[]) {
    List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
    System.out.println(totalValues(numbers, e -> true));
    System.out.println(totalValues(numbers, e -> e % 2 == 0));
    System.out.println(totalValues(numbers, e -> e % 2 != 0));


  }
}