How to sort alphanumeric keys in Hashmap in best possible manner?

问题

I have map like

Map<String,Integer> mp = new TreeMap<>();
        mp.put("R1", 00);
        mp.put("R0", 11);
        mp.put("R2", 22);
        mp.put("R3", 33);
        mp.put("R5", 55);
        mp.put("R8", 88);
        mp.put("R4", 44);
        mp.put("R6", 66);
        mp.put("R9", 99);
        mp.put("R7", 77);
        mp.put("R11", 1111);
        mp.put("R14", 1414);
        mp.put("R10", 1010);
        mp.put("R12", 1212);
        mp.put("R13", 1313);
        mp.put("R15", 1515);
        mp.put("R17", 1717);
        mp.put("R19", 1919);

I want to sort based upon keys. TreeMap is not working because of alphanumeric, getting output

{R0=11, R1=0, R10=1010, R11=1111, R12=1212, R13=1313, R14=1414, R15=1515, R17=1717, R19=1919, R2=22, R3=33, R4=44, R5=55, R6=66, R7=77, R8=88, R9=99}

Suggest how to do this?

回答1:

Create and pass to your TreeMap Comparator which will compare only integer part from keys (assuming that all keys are in form of R[number]).

In Java 8 your map can look like

Map<String, Integer> mp = new TreeMap<>(
        Comparator.comparingInt(key -> Integer.parseInt(key.substring(1))));

In Java 7 you can use rewrite it as

Map<String, Integer> mp = new TreeMap<>(new Comparator<String>(){
    @Override
    public int compare(String key1, String key2) {
               //parse only text after first letter
        int k1 = Integer.parseInt(key1.substring(1));
        int k2 = Integer.parseInt(key2.substring(1));
        return Integer.compare(k1, k2);
    }
});

It will order elements in a way:

{R0=11, R1=0, R2=22, R3=33, R4=44, R5=55, R6=66, R7=77, R8=88, R9=99, R10=1010, R11=1111, R12=1212, R13=1313, R14=1414, R15=1515, R17=1717, R19=1919}

回答2:

You can create an Set of Entry object from the Map. Then pass a custom Comparator to the Collections.sort() along with the Set. I have give the template below.

Set<Entry<String, Integer>> set = map.entrySet();
List<Entry<String, Integer>> list = new ArrayList<Entry<String, Integer>>(set);
Collections.sort( list, new Comparator<Map.Entry<String, Integer>>()
{
  public int compare( Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2 )
  {
    // Put your logic here for sorting.
  }
} );

You can use the regex or substring method from String for separating the chars and numbers from the String.

来源：https://stackoverflow.com/questions/32769266/how-to-sort-alphanumeric-keys-in-hashmap-in-best-possible-manner

标签

java

hashmap

treemap