Java 8 新特性 Lambda&Stream-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_42240545/article/details/120367402

本文通过具体示例展示了 Java 中 Stream API 的多种实用操作，包括过滤、映射、排序及统计等常见需求的实现方式，并提供了完整的代码示例。

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  List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd", "", "jkl");
        long count = strings.stream().filter(x -> x.contains("a")).count();
       List<String> a = strings.stream().filter(x -> x.contains("a")).collect( Collectors.toList());
      System.out.println(a);
      Random random=new Random();
       random.ints(10).forEach(System.out::println);
//map 方法用于映射每个元素到对应的结果，以下代码片段使用 map 输出了元素的整数值：
        List<Integer> collect = strings.stream().filter(a -> !a.isEmpty()).map(x -> x.length()).distinct().collect(Collectors.toList());
        System.out.println(collect);

      strings.stream().filter(a->!a.isEmpty()).sorted((x,y)->x.length()-y.length()).forEach(System.out::println);

        List<String> sortedcollect = strings.stream().filter(a -> !a.isEmpty()).sorted((x, y) -> x.length() - y.length()).collect(Collectors.toList());
        System.out.println(sortedcollect);

        List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
        System.out.println("=================================");
        numbers.stream().sorted().forEach(System.out::println);
        System.out.println("=================================");
        numbers.stream().sorted((x,y)->y-x).forEach(System.out::println);

        Map<Integer, Integer> collect = numbers.stream().distinct().collect(Collectors.toMap(str -> numbers.indexOf(str), str -> str));
        System.out.println(collect);

        IntSummaryStatistics intSummaryStatistics = numbers.stream().mapToInt(x -> x).summaryStatistics();
        System.out.println(intSummaryStatistics.getMax());
        System.out.println(intSummaryStatistics.getAverage());
         double payPercent=123.349;
         System.out.println((double)Math.round(payPercent*100)/100);
       // 然并卵 add by dt 17:36 2021/9/13
        double round = (double) Math.round((intSummaryStatistics.getAverage() * 100)) / 100;
        System.out.println(round);
       System.out.println( intSummaryStatistics.getAverage());
       System.out.println(intSummaryStatistics.getSum());
        System.out.println(intSummaryStatistics.getCount());
       System.out.println(intSummaryStatistics.getMin());


        Map map = new HashMap<String, String>();
        map.put("张三", "20");
        map.put("李四", "21");
        String name = "张三";
        map.forEach((key, val) -> {
            if ("张三".equals(key)) {
                System.out.println("存在数据-》键：" + key + "  值：" + val);
                return;
            }
        });

 List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd", "", "jkl");
        String a = Optional.ofNullable(strings)
                .filter(list -> CollectionUtils.isNotEmpty(list))
                .map(strings1 -> strings1.stream().filter(s -> !s.isEmpty()).collect(Collectors.toList()))
                .map(strings1 -> strings1.get(1))
                .orElse("");
        System.out.println(a);