摘要：
转载自:https://www.e-learn.cn/topic/2522732importlombok.Data;importjava.util.*;importjava.util.stream.Collectors;publicclassTestMain{//测试集合privateListnewsList=newArrayList();publicstaticvoidmain(
转载自: https://www.e-learn.cn/topic/2522732
importlombok.Data; import java.util.*; importjava.util.stream.Collectors; public classTestMain { //测试集合 private List<News> newsList = new ArrayList<>(); public static voidmain(String[] args) { TestMain testMain = newTestMain(); //初始集合 List<News> initList =testMain.newsList; //待赋值集合 List<News> otherList = new ArrayList<>(); //单个属性排序，按title字符串排序 List<News> titleSortList =initList.stream().sorted(Comparator.comparing(News::getTitle)).collect(Collectors.toList()); //多个属性排序, 按title、author字符串排序 thenComparing可以多个... List<News> titleAndAuthorSortList =initList.stream().sorted(Comparator.comparing(News::getTitle) .thenComparing(Comparator.comparing(News::getAuthor))) .collect(Collectors.toList()); //多个属性排序, 按title、hitNum倒序 List<News> titleAndHitsSortList =initList.stream().sorted(Comparator.comparing(News::getTitle) .thenComparing(Comparator.comparing(News::getHits).reversed())) .collect(Collectors.toList()); //多个属性排序，按title、hot排序降序，hot需转成数字进行排序 List<News> titleAndHotSortList =initList.stream().sorted(Comparator.comparing(News::getTitle) .thenComparing((v1, v2) ->Integer.valueOf(v2.getHot()).compareTo(Integer.valueOf(v1.getHot())))) .collect(Collectors.toList()); //集合过滤，hot大于30的数据 List<News> hotFilterList = initList.stream().filter(news -> news.getHits() > 30).collect(Collectors.toList()); //按照title/content字段进行去重 List<News> titleRepeatList =initList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection( () -> new TreeSet<>(Comparator.comparing(o -> o.title +o.content))), ArrayList::new)); //从 List 中取出title属性的组成 新的list 集合 List<String> titleList =initList.stream().map(News::getTitle).collect(Collectors.toList()); //List转Map key:title,value:content；使用去重后的集合防止key不唯一 Map<String, String> titleAndContentMap = titleRepeatList.stream().collect(Collectors.toMap(o -> o.getTitle(), o ->o.getContent())); //单个属性分组，title分组 Map<String, List<News>> titleMap =initList.stream().collect(Collectors.groupingBy(News::getTitle)); //多个属性分组，title、author分组，groupingBy可以为多个 Map<String, Map<String, List<News>>> titleAndAuthorMap =initList.stream().collect(Collectors.groupingBy(News::getTitle, Collectors.groupingBy(News::getAuthor))); //利用stream().map()处理List，并给另外一个List赋值 otherList = initList.stream().map(news -> {returnnews;}).collect(Collectors.toList()); //list遍历 initList.forEach(news ->{ System.out.println(news.getContent()); }); //map遍历 titleAndAuthorMap.forEach((k,v) ->{ System.out.println(k); Map<String, List<News>> map =v; }); } //代码块初始化数据 { int i = 50; while (i > 0) { //1-5随机数 int num = (int) (Math.random() * 5 + 1); //1-50随机数 int hitNum = (int) (Math.random() * 50 + 1); //1-500随机数 int hotNum = (int) (Math.random() * 500 + 1); News news = newNews(); news.setTitle("title" +num); news.setAuthor("author" +num); news.setContent("content" +num); news.setHits(hitNum); news.setHot(hotNum + ""); newsList.add(news); i--; } } /*** 测试内部类 */@Data classNews { //标题 privateString title; //作者 privateString author; //内容 privateString content; //点击数 private inthits; //热度 privateString hot; } }