What is the purpose of the PushbackInputStream class in Java?

PushbackInputStream is a decorator for input streams that allows you to "push back" (return) read bytes into the stream. This is useful when you need to read a few bytes to determine the next steps, and then push them back so that other code can process them from the beginning.

Example usage: parsing a stream where initial characters are read to determine the data format, and then the entire stream is processed.

It extends FilterInputStream. When created, a buffer is specified into which the returned bytes are placed. If the buffer is full, attempting to push back a byte will throw an IOException.