Interacting with Filesystems - Beginning Java 7 - page 738

close() methodbecause FilterOutputStream automaticallycallstheunderly-
ing output stream's close() method.
The makeMap() method is responsible for creating the map array that's passed to
ScrambledOutputStream 'sconstructor.Theideaistopopulatethearraywithall
256 byte integer values, storing them in random order.
Note I pass 0 as the seed argument when creating the java.util.Random
object inordertoreturnapredictable sequence ofrandomnumbers.Ineedtousethe
samesequenceofrandomnumberswhencreatingthecomplementarymaparrayinthe
Unscramble application, which I will present shortly. Unscrambling will not work
without the same sequence.
Supposeyouhaveasimple15-bytefilenamed hello.txt thatcontains“ Hello,
World! ” (followed by a carriage return and a line feed). When you execute java
Scramble hello.txt hello.out on an XP platform, you'll observe Figure
8-5 ' s scrambled output.
Figure 8-5. Different fonts yield different-looking scrambled output.
A filter input stream takesthedataobtainedfromitsunderlyinginputstream,which
mightbeanotherfilterinputstreamorasourceinputstreamsuchasafileinputstream,
filters it, and makes this data available via its read() methods (the output stream).
Filter input streams are created from subclasses of the concrete FilterIn-
putStream class, an InputStream subclass. FilterInputStream declares a
single FilterInputStream(InputStream in) constructorthatcreatesafilter
input stream built on top of in , the underlying input stream.
Listing8-11 showsthatit'seasytosubclass FilterInputStream .Atminimum,
declare a constructor that passes its InputStream argument to FilterIn-
putStream 'sconstructorandoverride FilterInputStream 's int read() and
int read(byte[] b, int off, int len) methods.
Listing 8-11. Unscrambling a stream of bytes