2020-11-05 java 8 stream().map List 对象里面某个数求和

info.getSysFiles().stream().mapToDouble(SysFile::getUsage).sum();

    String[] strs = { "aaa", "bbb", "ccc" };
    Arrays.stream(strs).map(str -> str.split("")).forEach(System.out::println);// Ljava.lang.String;@53d8d10a
    Arrays.stream(strs).map(str -> str.split("")).flatMap(Arrays::stream).forEach(System.out::println);// aaabbbccc

Collectors(): 类实现了很多归约操作，例如将流转换成集合和聚合元素。Collectors 可用于返回列表或字符串：

List<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
List<String> filtered = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.toList());
 
System.out.println("筛选列表: " + filtered);
String mergedString = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.joining(", "));
System.out.println("合并字符串: " + mergedString);