Musisz zastosować int.class, a nie Integer.class:
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.List;
public class Main {
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException,
InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
Class klasa = Class.forName("java.util.ArrayList");
final Class[] params = new Class[]{int.class};
Constructor constructor = klasa.getDeclaredConstructor(params);
List list = (List) constructor.newInstance(new Object[]{3});
list.add(5);
list.add("kupa");
System.out.println(list);
}
}