How do I use unread() in PushBackBufferedInputStream after the stream is empty?

Question

Making a Lexical Analyzer in Java and I'm using PushbackInputStream because I need to be able to push back what I read in case it's not what I wanted. But whenever the stream is empty and read() returns -1. It doesn't allow me to use unread().

EDIT: I'm currently using a regular InputStream, reading it all at once, putting it into a stack, and using the stack as the stream so I can pop() and push() items on it.

Answer 1

I think your problem is that you are using a crufty 3rd-party pushback stream.

You probably should be using java.io.PushbackInputStream or java.io.PushbackReader which have a more clearly specified API, and don't do peculiar things like "flushing" the buffer.

Answer 2

If you can get by with single token look-ahead and push-back, the quaintly venerable StreamTokenizer class may suffice. It's used in this simple implementation of a recursive descent parser.

Answer 3

But whenever the stream is empty and read() returns -1. It doesn't allow me to use unread().

Please elaborate 'doesn't allow me to use unread()'. From a quick look at the source code it should work OK.

Also curious to know why you are pushing back at EOF.