Code example for FileNotFoundException

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        } 
 
        public void renameTo(String from, String to) throws IOException {
            ByteBufferFile fromFile = files.get(from);
            if (fromFile == null)
                throw new FileNotFoundException(from);
            ByteBufferFile toFile = files.get(to);
            if (toFile != null) {
                files.remove(from);
            } 
            files.put(to, fromFile);
        } 
    } 
}