Multiple Values for a Key in Hashmap

Question

So I have a list of folder names that I want to separate by the keyword '-' and store then in a map. In that list of folder there might be multiple names before the '-' character so I want to get all the values that contains the same key and store that for that value. Also the name after '-' character might be different later on. For example, this is some of the folder names I have:

20190220103811-2019_Release_1
20190304201669-master
20190314142918-2019_Release_1
20190314143655-develop
20190315134912-2019_Release_1
20190315135106-develop
20190315143607-develop 

For all develop, I want to store the values for the develop key, and same for the rest. This is what I have so far:

File[] filteredDirectoryList = file.listFiles(textFilter);
        String[] splitArr = new String[filteredDirectoryList.length];
        ArrayList<String> listOfBuiltDate = new ArrayList<>();

        // looping through, splitting by '-' and adding it to a map
        for(File temp : filteredDirectoryList) {
            System.out.println(temp.getName());
            splitArr = temp.getName().split("-");


            if(temp.getName().contains(splitArr[1])) {
                listOfBuiltDate.add(splitArr[0]);
            }

            listOfDirectories.put(splitArr[1], listOfBuiltDate);
        }

My current output is:

Key=2019_Release_1, Value=[20190220103811, 20190304201669, 20190314142918, 20190314143655, 20190315134912, 20190315135106, 20190315143607]
Key=develop, Value=[20190220103811, 20190304201669, 20190314142918, 20190314143655, 20190315134912, 20190315135106, 20190315143607]
Key=master, Value=[20190220103811, 20190304201669, 20190314142918, 20190314143655, 20190315134912, 20190315135106, 20190315143607]

But I want it to be:

Key=2019_Release_1, Value=[20190220103811, 20190314142918, 20190315134912]
Key=develop, Value=[20190314143655, 20190315135106, 20190315143607]
Key=master, Value=[20190304201669]

I'm not sure how can I add the values to a list and add them to the map. I was thinking adding multiple lists that will only add based on each key (2019_Release_1) but there might be more keys so it might not be good.

Answer 1

Your approach is correct but you can't use the same List for all entries.

You must have a List for each Key

So your HashMap needs to change to:

HashMap<String, List<String>> listOfDirectories = new HashMap<>();

And then populate it like so:

for(File temp : filteredDirectoryList) {

    splitArr = temp.getName().split("-");

    //HERE IS WHERE YOU CREATE THE NEW LIST IF THE KEY DOESN'T HAVE IT
    if(!listOfDirectories.containsKey(splitArr[1])) {
        listOfDirectories.put(splitArr[1], new ArrayList<>());
    } 

    listOfDirectories.get(splitArr[1]).add(splitArr[0]);
}