Map<Key,Value>基于Value值排序

Author: giantray

README.md

@@ -23,6 +23,7 @@ stackoverflow-Java-top-qa
 * [如何将String转换为Int](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/converting-string-to-int-in-java.md)
 * [如何分割（split）string字符串](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-to-split-a-string-in-java.md)
 * [在java中如何对比（compare）string](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-do-i-compare-strings-in-java.md)
+* [Map<Key,Value>基于Value值排序](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-to-sort-a-mapkey-value-on-the-values-in-java.md)
 
 > 编程技巧
 
@@ -65,7 +66,6 @@ stackoverflow-Java-top-qa
 - [Initialization of an ArrayList in one line](http://stackoverflow.com/questions/1005073/initialization-of-an-arraylist-in-one-line)
 - [Java inner class and static nested class](http://stackoverflow.com/questions/70324/java-inner-class-and-static-nested-class)
 - ['Must Override a Superclass Method' Errors after importing a project into Eclipse](http://stackoverflow.com/questions/1678122/must-override-a-superclass-method-errors-after-importing-a-project-into-eclips)
-- [How to sort a Map<Key, Value> on the values in Java?](http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java)
 - [Declare array in Java?](http://stackoverflow.com/questions/1200621/declare-array-in-java)
 - [Fastest way to determine if an integer's square root is an integer](http://stackoverflow.com/questions/295579/fastest-way-to-determine-if-an-integers-square-root-is-an-integer)
 - [How to fix: Unsupported major.minor version 51.0 error?](http://stackoverflow.com/questions/10382929/how-to-fix-unsupported-major-minor-version-51-0-error)

contents/how-to-sort-a-mapkey-value-on-the-values-in-java.md

@@ -0,0 +1,77 @@
+##Map<Key,Value>基于Value值排序
+
+###方法1：
+使用TreeMap，可以参考下面的代码
+```java
+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  
+    }  
+}  
+```
+译注：如果不自己写Comparator,treemap默认是用key来排序
+
+###方法2：
+
+先通过linkedlist排好序，再放到LinkedHashMap中
+```java
+public class MapUtil  
+{  
+    public static <K, V extends Comparable<? super V>> Map<K, V>   
+        sortByValue( Map<K, V> map )  
+    {  
+        List<Map.Entry<K, V>> list =  
+            new LinkedList<Map.Entry<K, V>>( map.entrySet() );  
+        Collections.sort( list, new Comparator<Map.Entry<K, V>>()  
+        {  
+            public int compare( Map.Entry<K, V> o1, Map.Entry<K, V> o2 )  
+            {  
+                return (o1.getValue()).compareTo( o2.getValue() );  
+            }  
+        } );  
+  
+        Map<K, V> result = new LinkedHashMap<K, V>();  
+        for (Map.Entry<K, V> entry : list)  
+        {  
+            result.put( entry.getKey(), entry.getValue() );  
+        }  
+        return result;  
+    }  
+}  
+```
+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。
+
+stackoverflow链接：
+http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java