store key values of hashmap in string[] [duplicate]

问题

Got the solution.. Used linkedHashMap and was able to store the sorted key values in an array. Here's the link for the code.

Possible Duplicate:
store key values of sorted hashmap in string[]

I created a hashmap and then 'sorted by value' the elements in the map using this code. The code worked and i was able to display on screen the key value pairs sorted by value.

Now I want to store the keys(from the sorted elements) in a String[]. HashMap.keySet().toArray() doesn't help as the entired HashMap are not sorted.

Can anyone please suggest a method to do this?

further clarifying the situation - Suppose I have key value pairs like (a,1)(b,23)(c,7) by using the above link, i was able to get (a,1)(c,7)(b,23) as output. I want to store {a,c,b} as a string array. I hope the problem is clear now.

回答1:

Reusing this code you would just use

List keys = sortByValue(m);
String[] keyArray = keys.toArray(new String[keys.size()]);

Using generics would make this nicer. I would also sort by Map.Entry (from entrySet()) which would be faster and simpler.

回答2:

Sorting my keys is simple, use TreeMap.

TreepMap sortedMap = new TreeMap(someHashMap);
String[] sortedKeys = sortedMap.keySet().toArray();

回答3:

That code is not really sorting the HashMap - it is merely returning the keys, sorted by their value:

So all you need is:

Object[] key_array = sortByValue(m).toArray();

回答4:

I'd go either for something like

private static String[] keysSortedByValue(final Map<String, String> m) {
    final String[] result = m.keySet().toArray(new String[m.size()]);
     Arrays.sort(result, new Comparator<String>() {
         @Override
         public int compare(String o1, String o2) {
             final String v1 = m.get(o1);
             final String v2 = m.get(o2);
             if (v1==v2) return 0;
             if (v1==null) return -1;
             if (v2==null) return +1;
             return v1.compareTo(v2);
         }
     });
     return result;
}

or use Map.Entry[] for greater efficiency (avoiding the lookup).

回答5:

I would use Google Collection:

    Map<String, String> map = new HashMap<String, String>( );
    map.put("ABC1", "VALUE1");
    map.put("ABC7", "VALUE1");
    map.put("ABC2", "VALUE2");
    map.put("ABC3", "VALUE1");

    Multimap multimap = TreeMultimap.create();

    for(Map.Entry<String, String> entry: map.entrySet() ) {
         multimap.put( entry.getValue(), entry.getKey() );
    }


    System.out.println( Arrays.toString( multimap.values().toArray() ));

来源：https://stackoverflow.com/questions/7415366/store-key-values-of-hashmap-in-string

标签

java

hashmap