Question

There’s a common pattern, when each layer of application, dealing with data from a stream tends to wrap it into a BufferedInputStream, so that at a whole, there’s a lot of buffers, filled from buffers, filled from buffers and so on.

I think this is bad practice and want to question: how does it impact the performance? Can this cause bugs?

Answer 1

This is a very general question, but I’d say there are a number of problems with having lots of layers of buffered input streams (in any language).

• Each buffer takes up memory, even when it’s not filled. So, even if the data gets sucked right up to the top “layer” straight away, memory is still being needlessly used. (Note: I’m assuming that Java doesn’t resize its buffers automatically or anything — and I’m no Java expert.)
• Whenever you read from the top-level buffer, you’ll be setting off a big chain of method calls. Method calls involve indirection (i.e. pointer-following), passing-around of data (which could lead to poor caching performance), and so on.
• It probably means that the design isn’t very well-thought-out, since buffered streams should generally be for reading from sources that actually need buffering, like the disk or the network.

Just a few thoughts on the matter. I’m sure someone with better Java knowledge could contribute a more detailed analysis.