我对Java比较陌生,经常发现需要对值进行Map<Key,Value>排序。

由于这些值不是唯一的,我发现自己将keySet转换为一个数组,并使用自定义比较器通过数组排序对该数组进行排序,该比较器根据与该键关联的值进行排序。

有没有更简单的方法?


当前回答

public class SortedMapExample {

    public static void main(String[] args) {
        Map<String, String> map = new HashMap<String, String>();

        map.put("Cde", "C");
        map.put("Abc", "A");
        map.put("Cbc", "Z");
        map.put("Dbc", "D");
        map.put("Bcd", "B");
        map.put("sfd", "Bqw");
        map.put("DDD", "Bas");
        map.put("BGG", "Basd");

        System.out.println(sort(map, new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                    return o1.compareTo(o2);
            }}));
    }

    @SuppressWarnings("unchecked")
    public static <K, V> Map<K,V> sort(Map<K, V> in, Comparator<? super V> compare) {
        Map<K, V> result = new LinkedHashMap<K, V>();
        V[] array = (V[])in.values().toArray();
        for(int i=0;i<array.length;i++)
        {

        }
        Arrays.sort(array, compare);
        for (V item : array) {
            K key= (K) getKey(in, item);
            result.put(key, item);
        }
        return result;
    }

    public static <K, V>  Object getKey(Map<K, V> in,V value)
    {
       Set<K> key= in.keySet();
       Iterator<K> keyIterator=key.iterator();
       while (keyIterator.hasNext()) {
           K valueObject = (K) keyIterator.next();
           if(in.get(valueObject).equals(value))
           {
                   return valueObject;
           }
       }
       return null;
   }

}

//请在这里尝试。我正在修改值排序的代码。

其他回答

使用java.util.TreeMap。

映射根据其键的自然顺序进行排序,或由创建映射时提供的Comparator进行排序,具体取决于使用的构造函数

基于@devinmore代码,一种使用泛型并支持升序和降序排序的map排序方法。

/**
 * Sort a map by it's keys in ascending order. 
 *  
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByKey(final Map<K, V> map) {
    return sortMapByKey(map, SortingOrder.ASCENDING);
}

/**
 * Sort a map by it's values in ascending order.
 *  
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByValue(final Map<K, V> map) {
    return sortMapByValue(map, SortingOrder.ASCENDING);
}

/**
 * Sort a map by it's keys.
 *  
 * @param sortingOrder {@link SortingOrder} enum specifying requested sorting order. 
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByKey(final Map<K, V> map, final SortingOrder sortingOrder) {
    Comparator<Map.Entry<K, V>> comparator = new Comparator<Entry<K,V>>() {
        public int compare(Entry<K, V> o1, Entry<K, V> o2) {
            return comparableCompare(o1.getKey(), o2.getKey(), sortingOrder);
        }
    };

    return sortMap(map, comparator);
}

/**
 * Sort a map by it's values.
 *  
 * @param sortingOrder {@link SortingOrder} enum specifying requested sorting order. 
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByValue(final Map<K, V> map, final SortingOrder sortingOrder) {
    Comparator<Map.Entry<K, V>> comparator = new Comparator<Entry<K,V>>() {
        public int compare(Entry<K, V> o1, Entry<K, V> o2) {
            return comparableCompare(o1.getValue(), o2.getValue(), sortingOrder);
        }
    };

    return sortMap(map, comparator);
}

@SuppressWarnings("unchecked")
private static <T> int comparableCompare(T o1, T o2, SortingOrder sortingOrder) {
    int compare = ((Comparable<T>)o1).compareTo(o2);

    switch (sortingOrder) {
    case ASCENDING:
        return compare;
    case DESCENDING:
        return (-1) * compare;
    }

    return 0;
}

/**
 * Sort a map by supplied comparator logic.
 *  
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMap(final Map<K, V> map, final Comparator<Map.Entry<K, V>> comparator) {
    // Convert the map into a list of key,value pairs.
    List<Map.Entry<K, V>> mapEntries = new LinkedList<Map.Entry<K, V>>(map.entrySet());

    // Sort the converted list according to supplied comparator.
    Collections.sort(mapEntries, comparator);

    // Build a new ordered map, containing the same entries as the old map.  
    LinkedHashMap<K, V> result = new LinkedHashMap<K, V>(map.size() + (map.size() / 20));
    for(Map.Entry<K, V> entry : mapEntries) {
        // We iterate on the mapEntries list which is sorted by the comparator putting new entries into 
        // the targeted result which is a sorted map. 
        result.put(entry.getKey(), entry.getValue());
    }

    return result;
}

/**
 * Sorting order enum, specifying request result sort behavior.
 * @author Maxim Veksler
 *
 */
public static enum SortingOrder {
    /**
     * Resulting sort will be from smaller to biggest.
     */
    ASCENDING,
    /**
     * Resulting sort will be from biggest to smallest.
     */
    DESCENDING
}
    static <K extends Comparable<? super K>, V extends Comparable<? super V>>
    Map sortByValueInDescendingOrder(final Map<K, V> map) {
        Map re = new TreeMap(new Comparator<K>() {
            @Override
            public int compare(K o1, K o2) {
                if (map.get(o1) == null || map.get(o2) == null) {
                    return -o1.compareTo(o2);
                }
                int result = -map.get(o1).compareTo(map.get(o2));
                if (result != 0) {
                    return result;
                }
                return -o1.compareTo(o2);
            }
        });
        re.putAll(map);
        return re;
    }
    @Test(timeout = 3000l, expected = Test.None.class)
    public void testSortByValueInDescendingOrder() {
        char[] arr = "googler".toCharArray();
        Map<Character, Integer> charToTimes = new HashMap();
        for (int i = 0; i < arr.length; i++) {
            Integer times = charToTimes.get(arr[i]);
            charToTimes.put(arr[i], times == null ? 1 : times + 1);
        }
        Map sortedByTimes = sortByValueInDescendingOrder(charToTimes);
        Assert.assertEquals(charToTimes.toString(), "{g=2, e=1, r=1, o=2, l=1}");
        Assert.assertEquals(sortedByTimes.toString(), "{o=2, g=2, r=1, l=1, e=1}");
        Assert.assertEquals(sortedByTimes.containsKey('a'), false);
        Assert.assertEquals(sortedByTimes.get('a'), null);
        Assert.assertEquals(sortedByTimes.get('g'), 2);
        Assert.assertEquals(sortedByTimes.equals(charToTimes), true);
    }

重要说明:

此代码可以以多种方式中断。如果您打算使用提供的代码,请务必阅读注释以了解其含义。例如,值不能再通过其键检索。(get始终返回null。)


这似乎比前面所有的都容易得多。按如下方式使用TreeMap:

public class Testing {
    public static void main(String[] args) {
        HashMap<String, Double> map = new HashMap<String, Double>();
        ValueComparator bvc = new ValueComparator(map);
        TreeMap<String, Double> sorted_map = new TreeMap<String, Double>(bvc);

        map.put("A", 99.5);
        map.put("B", 67.4);
        map.put("C", 67.4);
        map.put("D", 67.3);

        System.out.println("unsorted map: " + map);
        sorted_map.putAll(map);
        System.out.println("results: " + sorted_map);
    }
}

class ValueComparator implements Comparator<String> {
    Map<String, Double> base;

    public ValueComparator(Map<String, Double> base) {
        this.base = base;
    }

    // Note: this comparator imposes orderings that are inconsistent with
    // equals.
    public int compare(String a, String b) {
        if (base.get(a) >= base.get(b)) {
            return -1;
        } else {
            return 1;
        } // returning 0 would merge keys
    }
}

输出:

unsorted map: {D=67.3, A=99.5, B=67.4, C=67.4}
results: {D=67.3, B=67.4, C=67.4, A=99.5}

我们只需像这样对地图进行排序

            Map<String, String> unsortedMap = new HashMap<String, String>();

    unsortedMap.put("E", "E Val");
    unsortedMap.put("F", "F Val");
    unsortedMap.put("H", "H Val");
    unsortedMap.put("B", "B Val");
    unsortedMap.put("C", "C Val");
    unsortedMap.put("A", "A Val");
    unsortedMap.put("G", "G Val");
    unsortedMap.put("D", "D Val");

    Map<String, String> sortedMap = new TreeMap<String, String>(unsortedMap);

    System.out.println("\nAfter sorting..");
    for (Map.Entry <String, String> mapEntry : sortedMap.entrySet()) {
        System.out.println(mapEntry.getKey() + " \t" + mapEntry.getValue());