java8-tutorial/src/com/winterbe/java8/samples/stream/Streams11.java at master · kenjava/java8-tutorial · GitHub

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package com.winterbe.java8.samples.stream;

import java.util.Arrays;
import java.util.List;

/**
 * @author Benjamin Winterberg
 */
public class Streams11 {

    static class Person {
        String name;
        int age;

        Person(String name, int age) {
            this.name = name;
            this.age = age;
        }

        @Override
        public String toString() {
            return name;
        }
    }

    public static void main(String[] args) {
        List<Person> persons =
            Arrays.asList(
                new Person("Max", 18),
                new Person("Peter", 23),
                new Person("Pamela", 23),
                new Person("David", 12));

//        test1(persons);
//        test2(persons);
//        test3(persons);
//        test4(persons);
//        test5(persons);
        test6(persons);
    }

    private static void test1(List<Person> persons) {
        persons
            .stream()
            .reduce((p1, p2) -> p1.age > p2.age ? p1 : p2)
            .ifPresent(System.out::println);    // Pamela
    }

    private static void test2(List<Person> persons) {
        Person result =
            persons
                .stream()
                .reduce(new Person("", 0), (p1, p2) -> {
                    p1.age += p2.age;
                    p1.name += p2.name;
                    return p1;
                });

        System.out.format("name=%s; age=%s", result.name, result.age);
    }

    private static void test3(List<Person> persons) {
        Integer ageSum = persons
            .stream()
            .reduce(0, (sum, p) -> sum += p.age, (sum1, sum2) -> sum1 + sum2);

        System.out.println(ageSum);
    }

    private static void test4(List<Person> persons) {
        Integer ageSum = persons
            .stream()
            .reduce(0,
                (sum, p) -> {
                    System.out.format("accumulator: sum=%s; person=%s\n", sum, p);
                    return sum += p.age;
                },
                (sum1, sum2) -> {
                    System.out.format("combiner: sum1=%s; sum2=%s\n", sum1, sum2);
                    return sum1 + sum2;
                });

        System.out.println(ageSum);
    }

    private static void test5(List<Person> persons) {
        Integer ageSum = persons
            .parallelStream()
            .reduce(0,
                (sum, p) -> {
                    System.out.format("accumulator: sum=%s; person=%s\n", sum, p);
                    return sum += p.age;
                },
                (sum1, sum2) -> {
                    System.out.format("combiner: sum1=%s; sum2=%s\n", sum1, sum2);
                    return sum1 + sum2;
                });

        System.out.println(ageSum);
    }

    private static void test6(List<Person> persons) {
        Integer ageSum = persons
            .parallelStream()
            .reduce(0,
                (sum, p) -> {
                    System.out.format("accumulator: sum=%s; person=%s; thread=%s\n",
                        sum, p, Thread.currentThread().getName());
                    return sum += p.age;
                },
                (sum1, sum2) -> {
                    System.out.format("combiner: sum1=%s; sum2=%s; thread=%s\n",
                        sum1, sum2, Thread.currentThread().getName());
                    return sum1 + sum2;
                });

        System.out.println(ageSum);
    }
}