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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>
Summary</H2>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">To
review the collections provided in the standard Java (1.0 and 1.1) library (
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BitSet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is not included here since it&#8217;s more of a special-purpose class):
</FONT><P></DIV>
<OL>
<LI><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">	An
<A NAME="Index898"></A>array
associates numerical indices to objects. It holds objects of a known type so
you don&#8217;t have to cast the result when you&#8217;re looking up an object.
It can be multidimensional, and it can hold primitives. However, its size
cannot be changed once you create it.
</FONT><LI><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">	A
<A NAME="Index899"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
also associates numerical indices to objects &#8211; you can think of arrays and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s
as random-access collections. The 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
automatically resizes itself as you add more elements. But a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
can hold only 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Object</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
handles, so it won&#8217;t hold primitives and you must always cast the result
when you pull an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Object</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
handle out of a collection.
</FONT><LI><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">	A
<A NAME="Index900"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Hashtable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is a type of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Dictionary</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
which is a way to associate, not numbers, but 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>objects</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
with other objects. A 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Hashtable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
also supports random access to objects, in fact, its whole design is focused
around rapid access.
</FONT><LI><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">	A
<A NAME="Index901"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Stack</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is a last-in, first-out (LIFO) queue.
</FONT></OL><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">If
you&#8217;re familiar with data structures, you might wonder why there&#8217;s
not a larger set of collections. From a functionality standpoint, do you really 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>need</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
a larger set of collections? With a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Hashtable,</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
you can put things in and find them quickly, and with an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Enumeration</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
you can iterate through the sequence and perform an operation on every element
in the sequence. That&#8217;s a powerful tool, and maybe it should be enough.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">But
a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Hashtable
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">has
no concept of order. 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s
and arrays give you a linear order, but it&#8217;s expensive to insert an
element into the middle of either one. In addition, queues, dequeues, priority
queues, and trees are about 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>ordering</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
the elements, not just putting them in and later finding them or moving through
them linearly. These data structures are also useful, and that&#8217;s why they
were included in Standard C++. For this reason, you should consider the
collections in the standard Java library only as a starting point, and, if you
must use Java 1.0 or 1.1, use the JGL when your needs go beyond that.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">If
you can use Java 1.2 you should use only the new collections, which are likely
to satisfy all your needs. Note that the bulk of this book was created using
Java 1.1, so you&#8217;ll see that the collections used through the rest of the
book are the ones that are available only in Java 1.1: 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Hashtable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
This is a somewhat painful restriction at times, but it provides better
backward compatibility with older Java code. If you&#8217;re writing new code
in Java 1.2, the new collections will serve you much better.
</FONT><a name="_Toc375545360"></a><a name="_Toc408018587"></a><P></DIV>

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