集合嵌套小案例

  Map<String, List<String>> map = new HashMap<>();
    List<String> list = new ArrayList<>();
    Collections.addAll(list,"A","B");
    map.put("张三",list);
    List<String> list1 = new ArrayList<>();
    Collections.addAll(list1,"B","C");
    map.put("李四",list1);
    List<String> list2 = new ArrayList<>();
    Collections.addAll(list2,"C","D");
    map.put("王五",list2);
    Map<String,Integer> maps = new HashMap<>();
    Collection<List<String>> values = map.values();

    for (List<String> value : values) {//遍历ArrayList集合的元素
        for (String s : value) {//遍历每个元素的值
            if(maps.containsKey(s)){
                maps.put(s,maps.get(s)+1);
            }else {
                maps.put(s,1);
            }
        }
    }
    System.out.println(maps);
}