Map之key和value排序

- 日理万妓 2022-05-31 06:07 285阅读 0赞

按照value排序，一般排序按照key的话，一般key都是Integer和String，用TreeMap就可以了，另外中方式是把Map按照Map.Entry取出来，放到List里面，然后借助Collectins的sort进行排序。  
代码：

/** * @author wzx * @time 2018/2/9 */
    public class MapSortTest { 
        public static void main(String[] args) {
            Pet p1 = new Pet("dog", 2);
            Pet p2 = new Pet("cat", 5);
            Pet p3 = new Pet("pig", 3);
            Pet p4 = new Pet("wolf", 1);
            Map<String, Pet> map = new HashMap<>();
            //Map<String, Pet> map = new TreeMap<String,Pet>();
            map.put("d", p1);
            map.put("c", p2);
            map.put("p", p3);
            map.put("w", p4);
            System.out.println(map);
            map = compareByValue(map);
            System.out.println(map);
    
            map = compareByKey(map);
            System.out.println(map);
    
            sortByKey(map);
            sortByKey2(map);
            sortByValue(map);
    
        }
    
        /** * 基本的value排序方式 * @param map * @return */
        public static Map compareByValue(Map map) {
            if (map == null || map.isEmpty()) {
                return null;
            }
            List<Map.Entry<String, Pet>> list = new ArrayList<Map.Entry<String, Pet>>(map.entrySet());
            Collections.sort(list, new MapValueComparator());
            Map<String, Pet> returnMap = new LinkedHashMap<>();
            for (Map.Entry<String, Pet> entry : list) {
                returnMap.put(entry.getKey(), entry.getValue());
            }
            return returnMap;
        }
    
    
        /** * 基本的key排序方式 * @param map * @return */
        public static Map compareByKey(Map map) {
            if (map == null || map.isEmpty()) {
                return null;
            }
            Map returnMap = new TreeMap<String, Pet>(new MapKeyComparator());
            returnMap.putAll(map);
            return returnMap;
        }
    
        static class MapKeyComparator implements Comparator<String> {
            @Override
            public int compare(String o1, String o2) {
                return o1.compareTo(o2);
            }
        }
    
        static class MapValueComparator implements Comparator<Map.Entry<String, Pet>> {
    
            @Override
            public int compare(Map.Entry<String, Pet> o1, Map.Entry<String, Pet> o2) {
                return o1.getValue().old - o2.getValue().old;
            }
        }
    
    }

**使用Java8中Map.Entry的新方法：**  
原理：map提取Entry的list之后转化成流（string()）,然后把流排序按照传入的Comparator排序。  
key排序：

public static void sortByKey(Map map) {
            List<Map.Entry<String, Pet>> compareByValue = (List<Map.Entry<String, Pet>>) map.entrySet()
                    .stream()
                    .sorted(Map.Entry.comparingByKey())
                    .collect(Collectors.toList());
            compareByValue.forEach(System.out::println);
            System.out.println("sortByKey: end");
        }

value排序：

public static void sortByValue(Map map) {
            List<Map.Entry<String, Pet>> compareByValue = (List<Map.Entry<String, Pet>>) map.entrySet()
                    .stream()
                    .sorted(Map.Entry.comparingByValue())
                    .collect(Collectors.toList());
            compareByValue.forEach(System.out::println);
        }

传入比较器参数：

public static void sortByKey2(Map map) {
            List<Map.Entry<String, Pet>> compareByValue = (List<Map.Entry<String, Pet>>) map.entrySet()
                    .stream()
                    .sorted(Map.Entry.comparingByValue((Pet pet1, Pet pet2) -> {
                        return pet1.name.length() - pet2.name.length();
                    }))
                    .collect(Collectors.toList());
            compareByValue.forEach(System.out::println);
            System.out.println("sortByKey2: end");
        }

> [http://blog.csdn.net/kaka0930/article/details/52996486\#\#\#][http_blog.csdn.net_kaka0930_article_details_52996486];

[http_blog.csdn.net_kaka0930_article_details_52996486]: http://blog.csdn.net/kaka0930/article/details/52996486###