IntSummaryStatistics summaryStatistics = Stream.of("1","2","3").collect(Collectors.summarizingInt(String::length));double average = summaryStatistics.getAverage();double max = summaryStatistics.getMax();double count = summaryStatistics.getCount();這個方法可以求出流中的最大最小值等。但如果流里的元素是int呢，是double呢，或者是包裝類又該怎么辦呢？還有String::length是干嘛的?。孔鼋y計操作和字符串的長度有什么關系呢？