Stream组合操作: reduce
将流中各元素进行聚合操作.
5.1 字符串连接, concat = "ABCD"
String concat = Stream.of("A", "B", "C",..."D").reduce("", String::concat);
5.2 求最小值, minValue = -3.0
double minValue = Stream.of(-1.5, 1.0, -3.0...= "ace"
concat = Stream.of("a", "B", "c", "D", "e", "F")
.filter(x -> x.compareTo("Z") > 0)
.reduce(..."", String::concat);
5.6 按年龄分组: groupingBy
Map map = Stream.of(new Person()).collect(Collectors.groupingBy...(string -> string.isEmpty()).count();