class IndexTimestamp {
    private Date lastModified;

    private static final Logger LOGGER = LoggerFactory.getLogger(IndexTimestamp.class);

    /**
     * Get the date of the last index update.
     *
     * @return the time of the last index update.
     */
    public Date getDateForLastIndexRun() {
        RuntimeEnvironment env = RuntimeEnvironment.getInstance();
        if (lastModified == null) {
            File timestamp = new File(env.getDataRootFile(), "timestamp");
            if (timestamp.exists()) {
                lastModified = new Date(timestamp.lastModified());
            }
        }
        return lastModified;
    }

    public void refreshDateForLastIndexRun() {
        lastModified = null;
    }

    public void stamp() throws IOException {<FILL_FUNCTION_BODY>}
}

        RuntimeEnvironment env = RuntimeEnvironment.getInstance();
        File timestamp = new File(env.getDataRootFile(), "timestamp");
        String purpose = "used for timestamping the index database.";
        if (timestamp.exists()) {
            if (!timestamp.setLastModified(System.currentTimeMillis())) {
                LOGGER.log(Level.WARNING, "Failed to set last modified time on ''{0}'', {1}",
                    new Object[]{timestamp.getAbsolutePath(), purpose});
            }
        } else {
            if (!timestamp.createNewFile()) {
                LOGGER.log(Level.WARNING, "Failed to create file ''{0}'', {1}",
                    new Object[]{timestamp.getAbsolutePath(), purpose});
            }
        }
    
<no_super_class>