Question

I’m getting a compiler error with this code:

Map<String, String[]> myMap;

void set(Map<String, Object> foo) { }

set(myMap); // generates error

Error: "The method set(Map<String,Object>) in the type XXX is not applicable for the arguments (Map<String,String[]>)"

This makes no sense to me, because String[] is in fact an Object, and is entirely compatible with the parameter in set().

This error did not show up in my code until I upgraded from JDK 1.6 to 1.7. I do not see a switch in Eclipse to turn it off. How do I get this code to compile?

Edit:

It does compile if I use an intermediate variable, and drop the generics:

Map anotherMap = myMap;
set(anotherMap);

Answer 1

Generics inheritance is different from our regular understanding of OO inheritance. Please read this tutorial.

To make your code compile, you may need to change your method syntax like below:

void set(Map<String, ?> foo) { }

EDIT: As dasblinkenlight commented, if you have any plans to do modifications to the Map inside the set method, it won’t work unless you have concrete type defined.