Filtering

You can read a stream thru a filter. This allows you either read selected parts of the stream or transform the contents.
For example, you might want to alter the order of some bytes, or read only some tags in an XML file, etc.
The PushBackInputStream implements a one-byte pushback with its unread() method.
The LineNumberReader keeps track of the number of lines read. You can get this number with getLineNumber().
Both PrintStream and PrintWriter use buffering. They flush on a println (with automatic flushing turned on) or a flush.