Question

I’m using a HashMap in which I use an ArrayList as a value.

Like this:

Map<Movie, List<Grades>> gradedMovies = new HashMap();

I’m trying to create a method with which I could iterate through the values to see if a key(movie) already exists. If it does, I would like to add a new value(grade) into the list that is assigned to the particular key(movie). Something like this:

public void addGrade(Movie movie, Grade grade) {
// stuff here }

Ultimately I wan’t to be able to print a Map which would display the Movies and its’ grades after they’ve been added to the map.

How is this accomplished? Or is my whole approach (using a Map) totally wrong?

Thanks for any assistance. (This is homework)

Answer 1

I think you’re on the right path, just make sure your movie object implements equals and hashCode so it can work as a true key for the hash map.

If you want pretty printing just implement the toString method.

public void addGrade(Movie movie, Grade grade) {
    if (!gradedMovies.containsKey(movie)) { 
        gradedMovies.put(movie, new ArrayList()); 
    }
    gradedMovies.get(movie).add(grade);
}

hope this helps, Cheers!