Java8的stream API与 C#的 LINQ 拓展方法对比

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            Date time1 = convertLocalDateToTimeZone(LocalDate.of(1990, 1, 1));
            //0
            Long count1 = list1.stream().filter(o -> o.getBirthday().equals(time1)).count();

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            Map<Sex, List<Person>> group1 = list1.stream().collect(Collectors.groupingBy(Person::getSex));
            Iterator it = group1.entrySet().iterator();
            while (it.hasNext()) {
                Map.Entry<Sex, List<Person>> groupByItem = (Map.Entry) it.next();
                Sex sex = groupByItem.getKey();
                out.println(sex);
                groupByItem.getValue().forEach(person -> {
                    out.println(new Gson().toJson(person));
                });
            }
/*
Вывод:
Male
{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"Male"}
Female
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"Female"}
X
{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"}
 */

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 Person after90 = list1.stream()
                    .filter(o -> o.getBirthday().after(convertLocalDateToTimeZone(LocalDate.of(1990, 1, 1))))
                    .findFirst()
                    .orElse(null);
            // null

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            list1.stream().forEach(o -> {
                //Можно работать с коллекцией внутри ForEach
                o.setSex(Sex.X);
            });
            list1.forEach(o -> {
                out.println(new Gson().toJson(o));
            });
/*
{"height":165,"weight":50,"identifier":"1","address":"北京","birthday":"Jan 1, 1981 12:00:00 AM","hobbies":["吃飯","逛街"],"sex":"X"}
{"height":170,"weight":50,"identifier":"2","address":"北京","birthday":"Feb 1, 1982 12:00:00 AM","hobbies":["吃飯","看電影"],"sex":"X"}
{"height":170,"weight":50,"identifier":"3","address":"北京","birthday":"Mar 1, 1983 12:00:00 AM","hobbies":["吃飯","上網"],"sex":"X"}
 */

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            //Метод max IntStream возвращает OptionalInt, нужно проверить, есть ли значение, прежде чем читать. getAsInt выдаст ошибку, когда isPresent=false. mapToLong, mapToDouble аналогичны
            OptionalInt maxHeightOption = list1.stream().mapToInt(Person::getHeight).max();
            //Конкатенация строк, sum, min, max, average чисел — все это специальные reduce.
            //Когда коллекция имеет длину 0, возвращается начальное значение Integer.MIN_VALUE. Начальное значение нельзя передавать случайно, причина мне пока не ясна
            int maxHeight = list1.stream().mapToInt(Person::getHeight).reduce(Integer.MIN_VALUE, Integer::max);
            out.println(maxHeight);
            if (maxHeightOption.isPresent()) {
                maxHeight = maxHeightOption.getAsInt();
                out.println(maxHeight);
            }
            //Оба способа записи параметров mapToInt одинаковы. Я предпочитаю следующий, но idea выдаст предупреждение
            OptionalInt minWeightOption = list1.stream().mapToInt(o -> o.getHeight()).min();
            int minWeight = list1.stream().mapToInt(o -> o.getHeight()).reduce(Integer.MAX_VALUE, Integer::min);

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            //Оба параметра skip и limit имеют тип long, обратите на это внимание
            list1.stream().skip(1L).limit(2L);

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list1.stream().map(Person::getIdentifier).distinct();

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            out.println("------------------------------------|По возрастанию|------------------------------------");
            list1 = list1.stream().sorted(Comparator.comparing(Person::getBirthday)).collect(Collectors.toList());
            out.println(new Gson().toJson(list1));
            list1 = list1.stream().sorted((left, right) -> left.getBirthday().compareTo(right.getBirthday())).collect(Collectors.toList());
            out.println(new Gson().toJson(list1));

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            out.println("------------------------------------|По убыванию|------------------------------------");
            list1 = list1.stream().sorted(Comparator.comparing(Person::getBirthday).reversed()).collect(Collectors.toList());
            out.println(new Gson().toJson(list1));
            list1 = list1.stream().sorted((left, right) -> right.getBirthday().compareTo(left.getBirthday())).collect(Collectors.toList());
            out.println(new Gson().toJson(list1));

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            out.println("------------------------------------|Пересечение list1 ∩ list2|------------------------------------");
            list1.stream().filter(o -> list2.contains(o)).collect(Collectors.toList());

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            out.println("------------------------------------|Объединение list1 ∪ list2 |------------------------------------");
            list1.addAll(list2);

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            out.println("------------------------------------|Разность list1 - list2|------------------------------------");
            list1.stream().filter(item1 -> !list2.contains(item1)).collect(Collectors.toList());

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            out.println("------------------------------------|Преобразование структуры данных|------------------------------------");
            List<Person> list3 = list1.stream().filter(o -> true).collect(Collectors.toList());
            ArrayList<Person> list4 = list1.stream().filter(o -> true).collect(Collectors.toCollection(ArrayList::new));
            Set<Person> list5 = list1.stream().filter(o -> true).collect(Collectors.toSet());
            Object[] list6 = list1.stream().toArray();
            Person[] list7 = list1.stream().toArray(Person[]::new);