lambda expression code is showing compilation error in Intellj

Question

this code is copied from a reference but it shows compilation error in Intellj:

Stream locales = Stream.of(Locale.getAvailableLocales());
            Map<String, Set<String>> countryToLanguages = locales.collect(
                    groupingBy(l -> l.getDisplayCountry(),
                            mapping(l -> l.getDisplayLanguage(),
                                    toSet())));

the compiler is seeing object named "l" and a java Object not as a locale; so it cann't understand the methods l.getDisplayCountry() and l.getDisplayLanguage().

also the Project SDK is java 8 and project language level is 8- lambdas, type annotations etc.

Or just don’t store streams in local variables at all. There’s no benefit in doing that, it only open the possibility to accidentally using a Stream twice. Further, if you have an array rather than varargs, prefer `Arrays.stream` over `Stream.of`: `Map> countryToLanguages = Arrays.stream(Locale.getAvailableLocales()).collect( groupingBy(l -> l.getDisplayCountry(), mapping(l -> l.getDisplayLanguage(), toSet())));` — Holger, Oct 14 '16 at 16:20
By the way, you can use method reference, then, there is no variable `l` to worry about its type: `Map> countryToLanguages = Arrays.stream( Locale.getAvailableLocales()) .collect( groupingBy(Locale::getDisplayCountry, mapping(Locale::getDisplayLanguage, toSet())));` — Holger, Oct 14 '16 at 16:22
Possible duplicate of [What is a raw type and why shouldn't we use it?](http://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it) — Alexis C., Oct 14 '16 at 17:39
@AlexisC. yes, i wrote this part and forget to specify the stream type. — Ahmed Abbas, Oct 14 '16 at 23:13
@AlexisC. i think this question is about fixing a compilation problem not about the general rule of raw type. do you still think it's a duplicate/ — Ahmed Abbas, Oct 14 '16 at 23:14
If you understand what a raw type is (which the duplicate is about), you'll understand why you have this compilation problem and how to fix it. — Alexis C., Oct 15 '16 at 08:30

Manish · Answer 1 · 2017-06-03T05:46:01.463

In intellij, You need to set Language Level (8) for each module as well. Project Structure -> Module -> Select Module -> Sources -> Language Level = 8

And if you want to change in POM directly

First- Add Properties

<properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>

second- Add Plugin

<plugin>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.5.1</version>
    <configuration>
        <source>1.8</source>
        <target>1.8</target>
    </configuration>
</plugin>

Got from, thanks to Anuj stop IntelliJ IDEA to switch java language level everytime the pom is reloaded (or change the default project language level)

lambda expression code is showing compilation error in Intellj

1 Answers1