Java HashMap: adding to arraylist

Question

I'm using the HashMap class and it looks like this:

HashMap<String, ArrayList<String>> fileRank = new HashMap<String, ArrayList<String>>();

I'm wondering how to add a new String into the Arraylist after the initial put.

fileRank.put(word, file1);

I would like to add file2 after file1 to the key: word from above.

Answer 1

You have to get the array list out first:

ArrayList<String> list = fileRank.get(word);
list.add(file1);

Of course, it becomes more complicated if you don't know whether there is an entry for that key yet.

ArrayList<String> list = fileRank.get(word);
if (list == null) {
    list = new ArrayList<String>();
    fileRank.put(word, list);
}
list.add(file1);

Answer 2

You ask the map for the value for a certain key, which is an ArrayList, on which you can call add.

String key = "myKey";
fileRank.put( key, new ArrayList<String>() );
//...
fileRank.get( key ).add( "a value");