What structure should I use to store key and list of possible values?

Question

I want to store information about filetype and possible files extension. What I want to do is if I provide file extension and this extension is on the list I will return key for it.

Eg:

Map<Filetype, List<String>> extensionMapping= new HashMap<>();
extensionMapping.put(Filetype.IMAGE, Arrays.asList("jpg", "jpeg"));
extensionMapping.put(Filetype.WORD, Arrays.asList("doc", "docx"));
extensionMapping.put(Filetype.EXCEL, Arrays.asList("xls", "xlsx", "xlsm"));
extensionMapping.put(Filetype.PPT, Arrays.asList("ppt", "pptx", "pptm"));`

And then I want to do something like this:

return extensionMapping.get().contains("jpg");

which for string "jpg" returns me Filetype.IMAGE.

Which collection should I use?

It seems like your extensions are unique per key, so I'd opt for a Map<String, FileType> where the key is the extension. — Jacob G.
– Jacob G., Commented Feb 12, 2019 at 20:19
Why not Map <String, Filetype> is that's you most common query? — daniu
– daniu, Commented Feb 12, 2019 at 20:20
I feel current one is also good `Map<Filetype, List<String>> — Ryuzaki L
– Ryuzaki L, Commented Feb 12, 2019 at 20:29
EnumMap is a better container for cases where the key is of a single Enum type. — YoYo
– YoYo, Commented Apr 23, 2019 at 13:31

fps · Accepted Answer · 2019-02-13 12:56:19Z

2

I would create a reverse map, with the keys being the extension and the values the file type:

Map<String, Filetype> byExtension = new HashMap<>();
extensionMapping.forEach((type, extensions) -> 
        extensions.forEach(ext -> byExtension.put(ext, type)));

Now, for a given extension, you simply do:

FileType result = byExtension.get("jpg"); // FileType.IMAGE

answered Feb 13, 2019 at 12:56

fps

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YoYo Over a year ago

This is probably the better answer. Here is another posting to a similar question, where the mapping is being made part of the enum through a static Map: stackoverflow.com/a/12659023/744133

Ryuzaki L · Accepted Answer · 2019-02-12 20:49:41Z

1

I mean you can do that now also by having same structure Map<Filetype, List<String>>. In Map any of values (which is List of strings contains "jpg") will return Filetype.IMAGE or else it will return Filetype.None

extensionMapping.entrySet().stream().filter(entry->entry.getValue().contains("jpg")).map(Map.Entry::getKey)
      .findFirst().orElse(Filetype.None);

edited Feb 12, 2019 at 20:49

answered Feb 12, 2019 at 20:25

Ryuzaki L

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