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javagenericsincompatibletypeerror

List of Class<? extends Foo> incompatible types

I'm working on this piece of code:

List<Class<? extends Foo>> models = new ArrayList<>();
    if (bar == 0)
        models = getRandomBlas(); // returns List<Bla>
    else 
        models = getRandomBlubs(); // returns List<Blub>

with:

public class Bla extends Foo { ... }
public class Blub extneds Foo { ... }

But I'm getting an Incompatible types: Found: 'java.util.List<Bla>', required: 'java.util.List<java.lang.Class<? extends Foo>'

Has anyone got an idea? To my knowledge, this is how the ? extends should work...

Solution

  • You're right. That is how ? extends works, but your list wants Class objects.

    • List<Class<? extends Foo>> can contain Class objects that represent subtypes of Foo (Foo.class, Bla.class, Blub.class).

    • List<? extends Foo> can contain objects that are subtypes of Foo.

    You want the second version.