Map之key和value排序

按照value排序，一般排序按照key的話，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取出來，放到List裡面，然後借助Collectins的sort進行排序。

代碼：

/**
 * @author wzx
 * @time 2018/2/9
 */
public class MapSortTest {
    public static void main(String[] args) {
        Pet p1 = new Pet("dog", );
        Pet p2 = new Pet("cat", );
        Pet p3 = new Pet("pig", );
        Pet p4 = new Pet("wolf", );
        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之後轉化成流（string()）,然後把流排序按照傳入的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);
    }
           

傳入比較器參數：

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###;