Class<? extends Callable<Integer>> clazz = (Class<? extends Callable<Integer>>) Class.forName(options.valueOf(className)).asSubclass(Callable.class);

Class<Callable<Integer>> classCI = ...;

Class<? extends Callable<Integer>> clazz =
    Class.forName(options.valueOf(className))
    .asSubclass(classCI);

Class<Callable<Integer>> classCI = (Class<Callable<Integer>>)Callable.class;

Object o = ...;
String s1 = (String)o; // may fail, no javac warning
String s2 = String.class.cast(o); // may fail, no javac warning

@SuppressWarning( "unchecked" )
Class<? Callable<Integer>> getClass(String className)
{
    Class clazz = Class.forName(className);
    via reflection, check generic super interfaces of clazz
    if there's no Callable<Integer> super interface
        throw "className is not a Callable<Integer>"

    // we have *checked*, the following cast is safe
    return (Class<? Callable<Integer>>)clazz;
}