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| 1 | +##Map<Key,Value>基于Value值排序 |
| 2 | + |
| 3 | +###方法1: |
| 4 | +使用TreeMap,可以参考下面的代码 |
| 5 | +```java |
| 6 | +public class Testing { |
| 7 | + |
| 8 | + public static void main(String[] args) { |
| 9 | + |
| 10 | + HashMap<String,Double> map = new HashMap<String,Double>(); |
| 11 | + ValueComparator bvc = new ValueComparator(map); |
| 12 | + TreeMap<String,Double> sorted_map = new TreeMap<String,Double>(bvc); |
| 13 | + |
| 14 | + map.put("A",99.5); |
| 15 | + map.put("B",67.4); |
| 16 | + map.put("C",67.4); |
| 17 | + map.put("D",67.3); |
| 18 | + |
| 19 | + System.out.println("unsorted map: "+map); |
| 20 | + |
| 21 | + sorted_map.putAll(map); |
| 22 | + |
| 23 | + System.out.println("results: "+sorted_map); |
| 24 | + } |
| 25 | +} |
| 26 | + |
| 27 | +class ValueComparator implements Comparator<String> { |
| 28 | + |
| 29 | + Map<String, Double> base; |
| 30 | + public ValueComparator(Map<String, Double> base) { |
| 31 | + this.base = base; |
| 32 | + } |
| 33 | + |
| 34 | + // Note: this comparator imposes orderings that are inconsistent with equals. |
| 35 | + public int compare(String a, String b) { |
| 36 | + if (base.get(a) >= base.get(b)) { |
| 37 | + return -1; |
| 38 | + } else { |
| 39 | + return 1; |
| 40 | + } // returning 0 would merge keys |
| 41 | + } |
| 42 | +} |
| 43 | +``` |
| 44 | +译注:如果不自己写Comparator,treemap默认是用key来排序 |
| 45 | + |
| 46 | +###方法2: |
| 47 | + |
| 48 | +先通过linkedlist排好序,再放到LinkedHashMap中 |
| 49 | +```java |
| 50 | +public class MapUtil |
| 51 | +{ |
| 52 | + public static <K, V extends Comparable<? super V>> Map<K, V> |
| 53 | + sortByValue( Map<K, V> map ) |
| 54 | + { |
| 55 | + List<Map.Entry<K, V>> list = |
| 56 | + new LinkedList<Map.Entry<K, V>>( map.entrySet() ); |
| 57 | + Collections.sort( list, new Comparator<Map.Entry<K, V>>() |
| 58 | + { |
| 59 | + public int compare( Map.Entry<K, V> o1, Map.Entry<K, V> o2 ) |
| 60 | + { |
| 61 | + return (o1.getValue()).compareTo( o2.getValue() ); |
| 62 | + } |
| 63 | + } ); |
| 64 | + |
| 65 | + Map<K, V> result = new LinkedHashMap<K, V>(); |
| 66 | + for (Map.Entry<K, V> entry : list) |
| 67 | + { |
| 68 | + result.put( entry.getKey(), entry.getValue() ); |
| 69 | + } |
| 70 | + return result; |
| 71 | + } |
| 72 | +} |
| 73 | +``` |
| 74 | +译注:这两种方法,我简单测试了下,如果map的size在十万级别以上,两者的耗时都是几百毫秒,第二个方法会快一些。否则,第一个方法快一些。因此,如果你处理的map,都是几十万级别以下的大小,两种方式随意使用,看个人喜欢了。 |
| 75 | + |
| 76 | +stackoverflow链接: |
| 77 | +http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java |
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