Question

I have an ArrayList with some entries as a value in a HashMap, how to add new values to it?

Thanks.Did it like this:

Map<String, ArrayList<String>> index = new HashMap<String, ArrayList<String>>();
void add(String kword, String... urls){
    if(index.containsKey(kword)){
        index.get(kword).addAll(Arrays.asList(urls));
    } else {
        index.put(kword, (ArrayList<String>) Arrays.asList(urls));
    }
}

Answer 1

Assuming that you have something along these lines:

Map<K, ArrayList<V>> map = new HashMap<K, ArrayList<V>>();

then this should allow you to add new values to any list that is contained as a value in the map:

map.get(listKey).add(newValue);

Naturally, you can also store the result of map.get(listKey) to a temporary variable to avoid the cost of map.get() when inserting multiple values:

List<V> list = map.get(listKey);

for (V value : newValues)
    list.add(value);