public void setOutDir(String outDir) {
        /* Check important, otherwise concatenation of two null strings
         * produces the "nullnull" String.
         */
        if (outDir != null) {
            this.outDir = outDir + System.getProperty("file.separator");
            File d = new File(outDir);
            if (!d.exists())
                if (!d.mkdirs())
                    Util.error("cant.create.dir", d.toString());
        }
    }