Best way to create a hashmap of arraylist

Question

I have one million rows of data in .txt format. the format is very simple. For each row:

user1,value1
user2,value2
user3,value3
user1,value4
...

You k

Answer 1

I Could not find any easy way. MultiMap is not always an option available. So I wrote something this.

public class Context extends HashMap {

    public V addMulti(K paramK, V paramV) {
        V value = get(paramK);
        if (value == null) {
            List list = new ArrayList();
            list.add(paramV);
            put(paramK, paramV);
        } else if (value instanceof List) {
            ((List)value).add(paramV);
        } else {
            List list = new ArrayList();
            list.add(value);
            list.add(paramV);
            put(paramK, (V) list);
        }
        return paramV;
    }
}