How print out the contents of a HashMap in ascending order based on its values?

Question

I have this HashMap that I need to print out in ascending order according to the values contained in it (not the keys

Answer 1

You'll need to make a list of the keys, sort them according to the corresponding values, then iterate over the sorted keys.

Map map = getMyMap();
List keys = new ArrayList(map.keySet());
Collections.sort(keys, someComparator);
for (String key: keys) {
    System.out.println(key + ": " + map.get(key));
}

As for what to use for someComparator, here are some handy, generic Comparator-creating routines I often find useful. The first one sorts by the values according to their natural ordering, and the second allows you to specify any arbitrary Comparator to sort the values:

public static >
        Comparator mapValueComparator(final Map map) {
    return new Comparator() {
        public int compare(K key1, K key2) {
            return map.get(key1).compareTo(map.get(key2));
        }
    };
}

public static 
        Comparator mapValueComparator(final Map map,
                                         final Comparator comparator) {
    return new Comparator() {
        public int compare(K key1, K key2) {
            return comparator.compare(map.get(key1), map.get(key2));
        }
    };
}