java8 Stream

	List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
    //统计集合的最大值，最小值，总和，平均值等
    IntSummaryStatistics stats = numbers.stream().mapToInt((x) -> x).summaryStatistics();
    System.out.println(stats);

    //统计个数
    Map<Integer, List<Integer>> collect = numbers.stream().collect(Collectors.groupingBy(Integer::intValue));
    for (Map.Entry<Integer, List<Integer>> integerListEntry : collect.entrySet()) {
        System.out.println(integerListEntry.getKey() +" > " +integerListEntry.getValue().size());
    }

    System.out.println("====================");
    //字符串拆分成list，统计个数，再倒序排序
    String str = "aaabbcccaccbbbbb";
    List<Map.Entry<String, Integer>> strCountList =
            Arrays.stream(str.trim().split("")).collect(Collectors
                    .groupingBy(st -> st,
                            Collectors.collectingAndThen(Collectors.toList(), List::size))).entrySet().stream()
                    .sorted(Map.Entry.<String, Integer>comparingByValue()
                            .reversed()).collect(Collectors.toList());

    //统计元素出现次数做多的
    strCountList.stream().findFirst().ifPresent(entry ->
            System.out.println("字母{" + entry.getKey() + "}出现的次数最多,出现{" + entry.getValue() + "}次"));

    for (Map.Entry<String, Integer> stringIntegerEntry : strCountList) {
        System.out.println(stringIntegerEntry.getKey() +" > " +stringIntegerEntry.getValue());
    }

    //字符串List统计个数
    List<String> list = Arrays.asList("zhangsan","lisi","wangbninwei","zhangsan","zhangsan","wangbninwei","留底","test");
    Map<String, Integer> collectName = list.stream().collect(Collectors.groupingBy(name -> name, Collectors.collectingAndThen(Collectors.toList(), List::size)));
    System.out.println(collectName);