CODEWITHSUNDEEP
javadictionaryguava
Jeira
Jeira

Reputation: 31

guava - map backed guava function

I want to create a read-only Map backed by a guava Function. I have a function which provides the value, given a key.

Function f = new Function() {
    public Object apply(final Object key) {
        return ...;
     }
};

Map m = mapBasedOnFunction(f); // is this possible with Guava?

m.get(some key); // the value is provided by the function

Is this possible with Guava?

I understand that iteration, size(), ... will not work, which is not required here. Actually, I only need the get() function to be functional.

Thank you very much.

Upvotes: 3

Views: 318

Answers (3)

MMascarin
MMascarin

Reputation: 568

I'm not really sure what your are trying to accomplish here but - like George mentioned - something like this should work:

public class FunctionMap extends HashMap<Object, Object> {
    private Function<Object, Object> function;

    public FunctionMap(Function<Object, Object> function) { this.function = function; }

    @Override
    public Object get(Object key) { return function.apply(key); }
}

Upvotes: 0

Andrejs
Andrejs

Reputation: 27735

You can do this with Maps.toMap but you need to supply an Iterable of keys.

Function f = ...
Set keys = ...
Map map = Maps.toMap( keys, f );

Without the keys the map can't really handle .size() or .entrySet().

Upvotes: 4

Sezin Karli
Sezin Karli

Reputation: 2525

AFAIK the inverse is possible. You use Functions.forMap() and give it a Map which this call turns into a Function that can work as a mapping table.

I'm not sure you can do that with Guava.

Upvotes: 1

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