private Path computeUserClassPath() {
        String cp = options.get(CLASSPATH);

        // CLASSPATH environment variable when run from `javac'.
        if (cp == null) cp = System.getProperty("env.class.path");

        // If invoked via a java VM (not the javac launcher), use the
        // platform class path
        if (cp == null && System.getProperty("application.home") == null)
            cp = System.getProperty("java.class.path");

        // Default to current working directory.
        if (cp == null) cp = ".";

        return new Path()
            .expandJarClassPaths(true)        // Only search user jars for Class-Paths
            .emptyPathDefault(new File("."))  // Empty path elt ==> current directory
            .addFiles(cp);
    }