class FileSystem {

	@Pure
	public static File addExtension(File filename, String extension) {
		if (filename != null && !hasExtension(filename, extension)) {
			String extent = extension;
			if (!"".equals(extent) && !extent.startsWith(EXTENSION_SEPARATOR)) { //$NON-NLS-1$
				extent = EXTENSION_SEPARATOR + extent;
			}
			return new File(filename.getParentFile(), filename.getName() + extent);
		}
		return filename;
	}

	private  FileSystem();

}