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<a href="http://www.bruceeckel.com/javabook.html">Bruce Eckel's Thinking in Java</a>
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<H2 ALIGN=LEFT>
Adding
attributes
<P>and
useful interfaces
</H2>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
use of layered objects to dynamically and transparently add responsibilities to
individual objects is referred to as the <A NAME="Index1029"></A><A NAME="Index1030"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>decorator</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
pattern. (Patterns
</FONT><A NAME="fnB47" HREF="#fn47">[47]</A><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
are the subject of Chapter 16.) The decorator pattern specifies that all
objects that wrap around your initial object have the same interface, to make
the use of the decorators transparent – you send the same message to an
object whether it’s been decorated or not. This is the reason for the
existence of the “filter” classes in the Java IO library: the
abstract “filter” class is the base class for all the decorators.
(A decorator must have the same interface as the object it decorates, but the
decorator can also extend the interface, which occurs in several of the
“filter” classes).
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Decorators
are often used when subclassing requires a large number of subclasses to
support every possible combination needed – so many that subclassing
becomes impractical. The Java IO library requires many different combinations
of features which is why the decorator pattern is a good approach. There is a
drawback to the decorator pattern, however. Decorators give you much more
flexibility while you’re writing a program (since you can easily mix and
match attributes), but they add complexity to your code. The reason that the
Java IO library is awkward to use is that you must create many classes –
the “core” IO type plus all the decorators – in order to get
the single IO object that you want.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
classes that provide the decorator interface to control a particular
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
or
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>OutputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
are the
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>FilterInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>FilterOutputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
– which don’t have very intuitive names. They are derived,
respectively, from
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>OutputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
and they are abstract classes, in theory to provide a common interface for all
the different ways you want to talk to a stream. In fact,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>FilterInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>FilterOutputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
simply mimic their base classes, which is the key requirement of the decorator.
</FONT><a name="_Toc375545387"></a><a name="_Toc408018614"></a><P></DIV>
<A NAME="Heading308"></A><H3 ALIGN=LEFT>
Reading
from an InputStream
<P>with
FilterInputStream
</H3>
<DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>FilterInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
classes accomplish two significantly different things.
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
allows you to read different types of primitive data as well as
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects. (All the methods start with “read,” such as
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>readByte( )</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>readFloat( )</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
etc.) This, along with its companion
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataOutputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
allows you to move primitive data from one place to another via a stream. These
“places” are determined by the classes in Table 10-1. If
you’re reading data in blocks and parsing it yourself, you won’t
need
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
but in most other cases you will want to use it to automatically format the
data you read.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
remaining classes modify the way an
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
behaves internally: whether it’s buffered or unbuffered, if it keeps
track of the lines it’s reading (allowing you to ask for line numbers or
set the line number), and whether you can push back a single character. The
last two classes look a lot like support for building a compiler (that is, they
were added to support the construction of the Java compiler), so you probably
won’t use them in general programming.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">You’ll
probably need to buffer your input almost every time, regardless of the IO
device you’re connecting to, so it would have made more sense for the IO
library to make a special case for unbuffered input rather than buffered input.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Table
10-3. Types of FilterInputStream
</B></FONT><P></DIV>
<DIV ALIGN=LEFT><TABLE BORDER>
<COLGROUP>
<COL width="76">
<COL width="121">
<COL width="144">
</COLGROUP>
<TR VALIGN="TOP">
<TD WIDTH=76 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Class</FONT><P></DIV>
</TD>
<TD WIDTH=121 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Function</FONT><P></DIV>
</TD>
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Constructor
Arguments
</FONT><P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">How
to use it
</FONT><P></DIV>
</TD>
</TR>
<A NAME="Index1031"></A><A NAME="Index1032"></A><TR VALIGN="TOP">
<TD WIDTH=76 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Data-InputStream</B></FONT><P></DIV>
</TD>
<TD WIDTH=121 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Used
in concert with
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataOutputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
so you can read primitives (int, char, long, etc.) from a stream in a portable
fashion.
</FONT><P></DIV>
</TD>
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStream</B></FONT><P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Contains
a full interface to allow you to read primitive types.
</FONT><P></DIV>
</TD>
</TR>
</TABLE></DIV>
<DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><A NAME="Index1033"></A><A NAME="Index1034"></A><P></DIV>
<DIV ALIGN=LEFT><TABLE BORDER>
<COLGROUP>
<COL width="76">
<COL width="121">
<COL width="144">
</COLGROUP>
<TR VALIGN="TOP">
<TD WIDTH=76 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Buffered-InputStream</B></FONT><P></DIV>
</TD>
<TD WIDTH=121 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Use
this to prevent a physical read every time you want more data. You’re
saying “Use a buffer.”
</FONT><P></DIV>
</TD>
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
with optional buffer size.
</FONT><P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
doesn’t provide an interface
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>per
se
</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
just a requirement that a buffer be used. Attach an interface object.
</FONT><P></DIV>
</TD>
</TR>
<A NAME="Index1035"></A><A NAME="Index1036"></A><TR VALIGN="TOP">
<TD WIDTH=76 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>LineNumber-InputStream</B></FONT><P></DIV>
</TD>
<TD WIDTH=121 COLSPAN=1 ROWSPAN=2 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Keeps
track of line numbers in the input stream; you can call
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>getLineNumber( )</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>setLineNumber(int)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><P></DIV>
</TD>
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStream</B></FONT><P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH=144 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
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