Java所提供的Map class並無提供任何排序(sort)的函式
所以必需自行撰寫，範例參考如下
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;
public class sortMap {
public static void main(String[] args){
Map<String, Integer> sortMap = new TreeMap<String, Integer>();
sortMap.put("N1", 5);
sortMap.put("N2", 3);
sortMap.put("N3", 1);
sortMap.put("N4", 2);
sortMap.put("N5", 4);
Collection<Integer> sortMapTmp = sortMap.values();
System.out.println("--unsort Map--");
printSortMap(sortMap);
sortMap = sortMapByComparator(sortMap);
System.out.println("--sorted Map--");
printSortMap(sortMap);
}
private static Map<String, Integer> sortMapByComparator(Map<String, Integer> unsortMap){
List<Entry<String, Integer>> list = new LinkedList<Entry<String, Integer>>(unsortMap.entrySet());
// Sorting the list based on values
Collections.sort(list, new Comparator<Entry<String, Integer>>()
{
public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2)
{
//若要由小排到大
//如果 o1 > o2 => 回傳 1
// o1 = o2 => 回傳 0
// o1 < o2 => 回傳 -1
return o1.getValue().compareTo(o2.getValue());
}
});
Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
for (Entry<String, Integer> entry : list)
{
sortedMap.put(entry.getKey(), entry.getValue());
}
return sortedMap;
}
private static void printSortMap(Map<String, Integer> sortMap){
for(Entry<String, Integer> entry : sortMap.entrySet()){
System.out.println("Key : " + entry.getKey() + " Value : "+ entry.getValue());
}
}
}
[Reference]
http://stackoverflow.com/questions/1448369/how-to-sort-a-treemap-based-on-its-values
