1，筛选数据

 List<String> list = Arrays.asList("apple", "banana", "orange", "grapefruit", "kiwi");
    list.stream()
         .filter(s -> s.length() >= 5)
         .forEach(System.out::println);

2，将集合中的每个字符串转换为大写，并收集到新的列表中：

List<String> list = Arrays.asList("apple", "banana", "orange", "grapefruit", "kiwi");
List<String> resultList = list.stream()
                              .map(String::toUpperCase)
                              .collect(Collectors.toList());
System.out.println(resultList);

3.统计集合中以字母"a"开头的字符串的数量：

List<String> list = Arrays.asList("apple", "banana", "orange", "grapefruit", "kiwi");
long count = list.stream()
                 .filter(s -> s.startsWith("a"))
                 .count();
System.out.println(count);

4.使用并行流来提高处理速度，筛选出长度小于等于5的字符串

List<String> list = Arrays.asList("apple", "banana", "orange", "grapefruit", "kiwi");
list.parallelStream()
    .filter(s -> s.length() <= 5)
    .forEach(System.out::println);

 5.使用 Stream 对集合中的整数求和：

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
int sum = numbers.stream()
                 .mapToInt(Integer::intValue)
                 .sum();
System.out.println(sum);