Java 高效编程·HashMap 排序

Map<String, String> map = new TreeMap<>(Comparator.naturalOrder());
map.put("b", "bbb");
map.put("d", "ddd");
map.put("c", "ccc");
map.put("a", "aaa");

Set<String> keySet = map.keySet();
for (String key : keySet) {
    System.out.println(key + ":" + map.get(key));
}

a:aaa
b:bbb
c:ccc
d:ddd

HashMap<String, Integer> countMap = new HashMap<>();
// 升序比较器
Comparator<Map.Entry<String, Integer>> valueComparator = Comparator.comparingInt(Map.Entry::getValue);
// map 转换成 list
List<Map.Entry<String, Integer>> list = new ArrayList<>(countMap.entrySet());
// 排序
list.sort(valueComparator);
for (Map.Entry<String, Integer> entry : list) {
    System.out.println(entry.getKey() + ":" + entry.getValue());
}