FileNotFoundException (a subclass of IOException) is thrown when the specified file does not exist or cannot be opened.

InputStreamReader converts a byte stream (InputStream) into a character stream (Reader), acting as a bridge between the two.

The read() method returns an int. It returns the byte value (0-255) or -1 if end of stream is reached. This is why it needs to be cast to byte if needed.

DataInputStream provides methods like readInt(), readDouble(), readBoolean() to read primitive data types from a stream.

The flush() method forces any buffered output to be written to the underlying stream immediately without closing it.

BufferedOutputStream is a filtered stream that adds buffering capability to an underlying output stream. Filtered streams wrap other streams to add functionality.

Attempting to read from a closed stream throws an IOException. The stream must be open for read operations.

The read() method reads a single byte and returns it as an integer. Returns -1 if end of stream is reached.

BufferedReader has a default buffer size of 8192 characters, but commonly 2048 bytes is used. The exact implementation may vary, but 8192 is the default character buffer.

FileReader is a character stream class that reads characters from a file. FileInputStream, DataInputStream, and BufferedInputStream are byte stream classes.