Question

this code doesn’t compile. I’m wondering what I am doing wrong:

private static Importable getRightInstance(String s) throws Exception {
 Class<Importable> c = Class.forName(s);
 Importable i = c.newInstance();
 return i;
}

where Importable is an interface and the string s is the name of an implementing class.
The compiler says:

./Importer.java:33: incompatible types
found   : java.lang.Class<capture#964 of ?>
required: java.lang.Class<Importable>
  Class<Importable> c = Class.forName(format(s));

thanks for any help!

All the solutions

Class<? extends Importable> c = Class.forName(s).asSubclass(Importable.class);

and

Class<? extends Importable> c = (Class<? extends Importable>) Class.forName(s);

and

Class<?> c = Class.forName(format(s));
Importable i = (Importable)c.newInstance();

give this error (that i don’t understand):

Exception in thread "main" java.lang.IncompatibleClassChangeError: class C1 
has interface Importable as super class

where C1 is actually implementing Importable (so it is theoretically castable to Importable).

Answer 1

Use a runtime conversion:

Class <? extends Importable>  c
    = Class.forName (s).asSubclass (Importable.class);

This will bark with an exception at runtime if s specifies a class that doesn’t implement the interface.