Map as a function parameter in java

Question

I am writing a function which takes two map as argument
Here is my code

    public static Map<String, ArrayList<String> > getFavouriteGenres(Map<String, ArrayList<String> > userMovies, Map<String, ArrayList<String> > movieGenres)
    {
        
        Map<String, ArrayList<String>> genreMovies = new HashMap<String, ArrayList<String>>();

        for (Map.Entry m:movieGenres.entrySet()){
            //ArrayList<String> list = m.getValue();  
            for (String mov:m.getValue()){
                ArrayList<String> l = genreMovies.containsKey(mov) ? genreMovies.get(mov):new ArrayList<String>();
                genreMovies.put(mov, l.add(m.getKey()));
            }                            
        }
    //other implementation

On compilation I am getting following error

StreamingApp.java:17: error: for-each not applicable to expression type
            for (String mov:m.getValue()){
                                      ^
  required: array or java.lang.Iterable
  found:    Object
StreamingApp.java:19: error: incompatible types: Object cannot be converted to String
                genreMovies.put(mov, l.add(m.getKey()));

How to solve it ?

you need for(Map.Entry<String, ArrayList<String>> m:movieGenres.entrySet()) — f1sh
– f1sh, Commented Oct 28, 2020 at 14:43

rzwitserloot · Accepted Answer · 2020-10-28 14:39:55Z

3

You are using Map.Entry as a raw type. That means all generics of it and anything derived from it are also blank. Thus, m.getValue() returns Object and not ArrayList<String>.

The solution is to add the generics appropriately:

for (Map.Entry<String, ArrayList<String>> m : movieGenres.entrySet()) {
    List<String> list = m.getValue();
   ...
}

that's a mouthful. Fortunately, you can write that a lot more simply:

for (var m : movieGenries.entrySet()) {
    List<String> list = m.getValue();
    ...
}

answered Oct 28, 2020 at 14:39

rzwitserloot

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3 Comments

rzwitserloot Over a year ago

Well, then the first mouthful is the only solution, which fortunately is in the answer, so not sure if that's worth mentioning.

vsfDawg Over a year ago

Perhaps adding a note like "If you are using Java 10 or later..." since the OP did not indicate version.

aquib nawaz Over a year ago

I have java 11.

Monis · Accepted Answer · 2020-10-28 14:40:39Z

1

Change

for (Map.Entry m:movieGenres.entrySet()){

TO

for (Map.Entry<String, ArrayList<String>> m:movieGenres.entrySet()){

AND

genreMovies.put(mov, l.add(m.getKey()));

TO

l.add(m.getKey());
genreMovies.put(mov, l);

answered Oct 28, 2020 at 14:40

Monis

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