Testing Lambda in Java 8

Question

I am messing around with Java 8 lambda and I was trying to do the following but apparently I am doing something very wrong. I have an array of string String [] q and I was trying to call a static method that returns a set of Node objects for each element in the array. Here is what I wrote:

Set<Set<Node>> sets = Arrays.asList(q).stream().forEach(InMemoryGraph::getAllPredicates);

getAllPredicates is a method that accepts a String as an argument and returns a Set<Node> Do I need to use java.util.function? Any suggestion is appreciated.

Just to be sure, getAllPredicates is a static method, right? — Joffrey
– Joffrey, Commented Apr 21, 2014 at 9:55

assylias · Accepted Answer · 2014-04-21 00:20:25Z

3

So:

you have an array which you want to stream: Arrays.stream(q)
then you want to map each string to a set of node: .map(InMemoryGraph::getAllPredicates)
and collect those sets in a set: .collect(toSet());

in one go:

Set<Set<Node>> sets = Arrays.stream(q) //a Stream<String>
                       .map(InMemoryGraph::getAllPredicates) // a Stream<Set<Node>>
                       .collect(toSet()); // a Set<Set<Node>>

Note: you need a static import of Collectors.toSet.

edited Apr 21, 2014 at 0:20

answered Apr 21, 2014 at 0:06

assylias

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6 Comments

AR5HAM Over a year ago

Somehow the compiler doesn't like InMemoryGraph::getAllPredicates, it keeps asking to define a local variable or a field with the name InMemoryGraph, which is the name of the class. getAllPredicates is a public static method in that class. Any ideas?

assylias Over a year ago

Do you need to import the class maybe?

assylias Over a year ago

You could also try the equivalent lambda: .map(s -> InMemoryGraph.getAllPredicates(s)) and see what message you get. Can you confirm that the method signature is public static Set<Node> getAllPredicates(String s)?

AR5HAM Over a year ago

this line is in another static method within the same class. I used s -> InMemoryGraph.getAllPredicates(s) as well it says create a local variable called s!!

assylias Over a year ago

@Arsham are you sure you are compiling for Java 8 (and not Java 7)? Have you managed to create a simple program with a lambda?

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