chap02.htm

Thinking in Java, 2nd edition

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</FONT><LI><FONT FACE="Verdana"><B>	</B></FONT><FONT FACE="Georgia"><B>Non-RAM
storage</B>. If data lives completely outside a program it can exist while the
program is not running, outside the control of the program. The two primary
examples of this are <I>streamed objects,</I> in which objects are turned into
streams of bytes, generally to be sent to another machine, and <I>persistent
objects, </I>in which the objects are placed on disk so they will hold their
state even when the program is terminated. The trick with these types of storage
is turning the objects into something that can exist on the other medium, and
yet can be resurrected into a regular RAM-based object when necessary. Java
provides support for <I>lightweight persistence</I>, and future versions of Java
might provide more complete solutions for persistence.

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</FONT><A NAME="_Toc375545220"></A><A NAME="_Toc481064513"></A></OL><A NAME="Heading89"></A><FONT FACE = "Verdana"><H3 ALIGN="LEFT">
Special case: primitive
types<BR><A NAME="Index184"></A><A NAME="Index185"></A></H3></FONT>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">There is a group of types that gets
special treatment; you can think of these as &#8220;primitive&#8221; types that
you use quite often in your programming. The reason for the special treatment is
that to create an object with <B>new</B>&#8212;especially a small, simple
variable&#8212;isn&#8217;t very efficient because <B>new</B> places objects on
the heap. For these types Java falls back on the approach taken by C and C++.
That is, instead of creating the variable using <B>new</B>, an
&#8220;automatic&#8221; variable is created that <I>is not a reference</I>. The
variable holds the value, and it&#8217;s placed on the stack so it&#8217;s much
more efficient. 
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</FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Java determines the size of each
primitive type. These sizes don&#8217;t change from one machine architecture to
another as they do in most languages. This size invariance is one reason Java
programs are so portable.  
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<backtalk:display ID=TIJ3_CHAPTER2_I19>
</FONT><BR></P></DIV>
<DIV ALIGN="CENTER"><TABLE BORDER>
<TR VALIGN="TOP">
<TH WIDTH=72 COLSPAN=1 ROWSPAN=1 VALIGN="TOP">
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Primitive type</B></FONT><BR></P></DIV>
</TH>
<TH WIDTH=45 COLSPAN=1 ROWSPAN=1 VALIGN="TOP">
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Size</B></FONT><BR></P></DIV>
</TH>
<TH WIDTH=72 COLSPAN=1 ROWSPAN=1 VALIGN="TOP">
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Minimum</B></FONT><BR></P></DIV>
</TH>
<TH WIDTH=85 COLSPAN=1 ROWSPAN=1 VALIGN="TOP">
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Maximum</B></FONT><BR></P></DIV>
</TH>
<TH WIDTH=78 COLSPAN=1 ROWSPAN=1 VALIGN="TOP">
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Wrapper type</B></FONT><BR></P></DIV>
</TH>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>boolean</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">&#8212;</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">&#8212;</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">&#8212;</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Boolean</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>char</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">16-bit</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Unicode 0</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Unicode 2<SUP>16</SUP>-
1</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Character</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>byte </B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">8-bit</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">-128</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">+127</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Byte</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>short</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">16-bit</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">-2<SUP>15</SUP></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">+2<SUP>15</SUP>&#8212;1</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Short</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>int</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">32-bit</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">-2<SUP>31</SUP></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">+2<SUP>31</SUP>&#8212;1</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Integer</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>long</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">64-bit</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">-2<SUP>63</SUP></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">+2<SUP>63</SUP>&#8212;1</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Long</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>float</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">32-bit</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">IEEE754</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">IEEE754</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Float</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>double</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">64-bit </FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">IEEE754</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">IEEE754</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Double</B></FONT><BR></P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>void</B></FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">&#8212;</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">&#8212;</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">&#8212;</FONT><BR></P></DIV>
</TD>
<TD>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><B>Void</B></FONT><BR></P></DIV>
</TD>
</TR>
</TABLE></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">All numeric types are signed, so
don&#8217;t go looking for unsigned types.

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</FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">The size of the <B>boolean</B> type is
not explicitly defined; it is only specified to be able to take the literal
values <B>true</B> or <B>false</B>.</FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">The primitive data types also have
&#8220;wrapper&#8221;<I> </I>classes for them. That means that if you want to
make a nonprimitive object on the heap to represent that primitive type, you use
the associated wrapper. For example:

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</FONT><BR></P></DIV>

<BLOCKQUOTE><FONT SIZE = "+1"><PRE><font color=#0000ff>char</font> c = 'x';
Character C = <font color=#0000ff>new</font> Character(c);</PRE></FONT></BLOCKQUOTE>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Or you could also use:</FONT><BR></P></DIV>

<BLOCKQUOTE><FONT SIZE = "+1"><PRE>Character C = <font color=#0000ff>new</font> Character('x');</PRE></FONT></BLOCKQUOTE>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">The reasons for doing this will be shown
in a later chapter. 
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</FONT><BR></P></DIV>
<A NAME="Heading90"></A><FONT FACE = "Verdana"><H4 ALIGN="LEFT">
High-precision numbers</H4></FONT>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Java includes two classes for performing
high-precision arithmetic: <B>BigInteger</B> and <B>BigDecimal</B>. Although
these approximately fit into the same category as the &#8220;wrapper&#8221;
classes, neither one has a primitive analogue.

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</FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Both classes have methods that provide
analogues for the operations that you perform on primitive types. That is, you
can do anything with a <B>BigInteger</B> or <B>BigDecimal </B>that you can with
an <B>int</B> or <B>float</B>, it&#8217;s just that you must use method calls
instead of operators. Also, since there&#8217;s more involved, the operations
will be slower. You&#8217;re exchanging speed for accuracy.