In Java, the BufferedOutputStream class is a subclass of the FilterOutputStream that provides buffering functionality to an output stream. It writes data to an underlying output stream and stores it in an internal buffer for faster access.

Here are some of the commonly used methods of the BufferedOutputStream class:

1. write(int b): This method writes a single byte of data to the output stream.

2. write(byte[] b): This method writes b.length bytes of data to the output stream from an array of bytes.

3. write(byte[] b, int off, int len): This method writes len bytes of data to the output stream from an array of bytes starting at the specified offset off.

4. flush(): This method flushes the internal buffer and writes any remaining data to the output stream.

5. close(): This method closes the output stream and releases any system resources associated with it.

It's important to note that the BufferedOutputStream class should be used with caution when writing to untrusted destinations, as it can be vulnerable to malicious attacks if the data is not properly validated. Additionally, when using a BufferedOutputStream, you should always make sure to call the flush() method or close the stream to ensure that all the data is written to the underlying stream.