I'm trying to migrate some old applications that uses Java 8 libs to Java 11, but something strange happened with code that uses method references:
Error:(26, 46) java: incompatible types: cannot infer type-variable(s) R
(argument mismatch; invalid method reference
unexpected static method getId(com.mongodb.BasicDBObject) found in unbound lookup)
The scenario looks like this:
MyOldLib.java (on Java 8 project)
public class MyOldLib {
public static String getId(BasicDBObject o) { return o.getString("id"); }
}
MyMigratingApplication.java (on Java 11 project)
public class MyMigratingApplication {
public static void main(String[] args) {
List<BasicDBObject> myList = getDataFromSomewhere();
List<String> myIdList = myList.stream().map(MyOldLib::getId).collect(Collectors.toList());
//...
}
}
Using the method reference as was done doesn't work, but if I use a lambda or encapsulate the getId method instead, it does work:
Using lambda:
public class MyMigratingApplication {
public static void main(String[] args) {
List<BasicDBObject> myList = getDataFromSomewhere();
List<String> myIdList = myList.stream().map(data -> MyOldLib.getId(data)).collect(Collectors.toList());
//...
}
}
Encapsulating:
public class MyMigratingApplication {
static String getId(BasicDBObject data) {
return MyOldLib.getId(data)
}
public static void main(String[] args) {
List<BasicDBObject> myList = getDataFromSomewhere();
List<String> myIdList = myList.stream().map(MyMigratingApplication::getId).collect(Collectors.toList());
//...
}
}
Why is this happening? There's any solution that minimizes the code refactor needs?
Some aditional info:
1) The MongoDB version is the same on both projects, 3.6.4.
2) This happens when I try to run the applicatin on IntelliJ IDE.
3) I'm using Maven as dependency manager.
