Java8 Stream

// 数组形式获取流
String[] dataArrs = new String[10];
Stream<String> stream = Arrays.stream(dataArrs);
// 集合方式创建
List<String> dataList = new ArrayList<>();
// 获取一个顺序流
Stream<String> stream = dataList.stream();
 // 获取一个并行流
Stream<String> parallelStream = dataList.parallelStream();

// of 创建 stream
Stream<String> strs = Stream.of("a","b","c","d");
// lambda 创建等差数列，获取前 3 个
Stream<Integer> stream2 = Stream.iterate(1, (x) -> x + 4).limit(3);
stream2.forEach(System.out::println); // 1 5 9
// 随机获取三个随机数
Stream<Double> stream3 = Stream.generate(Math::random).limit(3);
stream3.forEach(System.out::println);

Stream<String> strs = Stream.of("a","b","c","d","d","e","f");
// 过滤大于b 的字符串并进行去重操作，跳过前两个并选取两个进行输出
Stream<String> result = strs.filter(s -> s.compareTo("b") > 0)
                .distinct()
                .skip(2)
                .limit(2);
// 输出结果 e 和 f
result.forEach(System.out::println);
// flatMap 的操作
List<String> list = Arrays.asList("e,f,g", "1,2,3");
// 利用map去除每个元素中的逗号
Stream<String> st1 = list.stream().map(s -> s.replaceAll(",", ""));
st1.forEach(System.out::println); // efg  123
// 利用 flatMap 将字符串进行分割
Stream<String> st2 = list.stream().flatMap(ele -> {
    //将每个元素转换成一个stream
    String[] split = ele.split(",");
    return Arrays.stream(split);
});
st2.forEach(System.out::println); // e f g 1 2 3
// 排序操作
List<String> list = Arrays.asList("aa", "ff", "dd");
//String 类自身已实现Compareable接口 aa dd ff
list.stream().sorted().forEach(System.out::println);

// match 操作 findFirst  findAny  count max min 操作
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
// 返回结果 false
boolean allMatch = list.stream().allMatch(e -> e > 10);
// 返回结果 true
boolean noneMatch = list.stream().noneMatch(e -> e > 10);
// 返回结果 true
boolean anyMatch = list.stream().anyMatch(e -> e > 4);
// 查找第一个或者随机获取
Integer findFirst = list.stream().findFirst().get();
Integer findAny = list.stream().findAny().get();
// 统计数据 个数为 5 最大值为 5 最小值为 1
long count = list.stream().count();
Integer max = list.stream().max(Integer::compareTo).get();
Integer min = list.stream().min(Integer::compareTo).get();
// reduce 操作
List<Integer> list = Arrays.asList(1, 2, 3);
// 该操作即是 累加求和，结果为 6
Integer result = list.stream().reduce((x1, x2) -> x1 + x2).get();
System.out.println(result);
// 标签
List<String> tags1 = Lists.newArrayList("a", "b", "c");
List<String> tags2 = Lists.newArrayList("d", "e", "f");
// 创建对象
User user1 = new User("小明", 12, tags1, BigDecimal.valueOf(43));
User user2 = new User("小李", 14, tags2, BigDecimal.valueOf(43));
// 声明数组对象
List<User> userList = Lists.newArrayList(user1, user2);
// 年龄和体重数据
List<Integer> ageList = userList.stream().map(User::getAge).collect(Collectors.toList());
Set<BigDecimal> weightSet = userList.stream().map(User::getWeight).collect(Collectors.toSet());
// 建立姓名年龄映射
Map<String, Integer> nameAgeMap = userList.stream().collect(Collectors.toMap(User::getName,User::getAge, (k1, k2) -> k2));
// flatMap 获取所有的标签
List<String> tagsList = userList.stream().flatMap(node -> node.getTags().stream().map(String::intern)).distinct().collect(Collectors.toList());
// 按照年龄分组
Map<Integer, List<User>> ageMap = userList.stream().collect(Collectors.groupingBy(User::getAge));
// 分区分成两部分，一部分大于10岁，一部分小于等于10岁
Map<Boolean, List<User>> partMap = userList.stream().collect(Collectors.partitioningBy(v -> v.getAge() > 10));
//规约 reduce
Integer sumAge = userList.stream().map(User::getAge).collect(Collectors.reducing(Integer::sum)).get();