Interacting with Filesystems - Beginning Java 7 - page 734

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FilterOutputStream and FilterInputStream
Filestreamspassbytesunchangedtotheirdestinations.Javaalsosupports filter streams
that buffer, compress/uncompress, encrypt/decrypt, or otherwise manipulate an input
stream's byte sequence before it reaches its destination.
A filter output stream takes the data passed to its write() methods (the input
stream), filters it, and writes the filtered data to an underlying output stream, which
mightbeanotherfilteroutputstreamoradestinationoutputstreamsuchasafileoutput
stream.
Filter output streams are created from subclasses of the concrete FilterOut-
putStream class,an OutputStream subclass. FilterOutputStream declares
asingle FilterOutputStream(OutputStream out) constructorthatcreatesa
filter output stream built on top of out , the underlying output stream.
Listing8-9 revealsthatit'seasytosubclass FilterOutputStream .Atminimum,
declare a constructor that passes its OutputStream argument to FilterOut-
putStream 's constructor and override FilterOutputStream 's void
write(int b) method.
Listing 8-9. Scrambling a stream of bytes
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
class ScrambledOutputStream extends FilterOutputStream
{
private int[] map;
ScrambledOutputStream(OutputStream out, int[] map)