CODEWITHSUNDEEP
javalambdamaps
Apollocy
Apollocy

Reputation: 77

How to run a lambda expression that is a value on a map

I'm quite new to java and I am trying to create a set out of objects that are acquired through lambda expressions in a map. Basically, I am getting a value from the map (lambda expression) and running it to get a Boolean. However, I'm getting an error when running the .apply on the expression. Any ideas on how to fix this? Any help is appreciated.

        Map<String, Predicate<IndexSub>> order_function = new HashMap<>();
        order_function.put("AlternativesValues", x -> false);
        order_function.put("AlternativesConstituent", x -> x.getCloseCons());
        order_function.put("EquityValues", x -> false);
        order_function.put("EquityCloseConstituent", x -> x.getCloseCons());
        order_function.put("EquityOpenConstituent", x -> x.getOpenCons());
        order_function.put("FixedValues", x -> false);
        order_function.put("FixedReturns", x -> x.getCloseCons());
        order_function.put("FixedStatistics", x -> x.getOpenCons());

        //getCloseCons and getOpenCons return true/false    

        Set<String> orderable_sub = new HashSet<String>();

        for (IndexSub s : tenant_subscriptions) {
                                 //DataProduct is a string
            if (order_function.get(DataProduct).apply(s) == true){
                orderable_sub.add(s.getIndexId());
            }

        }

Upvotes: 0

Views: 965

Answers (2)

Thomas
Thomas

Reputation: 88707

Since you seem to apply the same predicate to all elements in tenant_subscriptions you could use a stream:

Predicate<IndexSub> p = order_function.get(dataProduct);

if( p == null ) {
  //handle that case, e.g. set a default predicate or skip the following part
}

//this assumes tenant_subscriptions is a collection, if it is an array use Arrays.stream(...) or Stream.of(...)
Set<String> orderable_sub = tenant_subscriptions.stream() //create the stream
                               .filter(p) //apply the predicate
                               .map(IndexSub::getIndexId) //map all matching elements to their id
                               .collect(Collectors.toSet()); //collect the ids into a set

Upvotes: 0

Karol Dowbecki
Karol Dowbecki

Reputation: 44952

Predicate functional interface has test() method, not apply():

if (order_function.get(DataProduct).test(s)){
    orderable_sub.add(s.getIndexId());
}

Upvotes: 2

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