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学习java的经典书籍

    x = a.listIterator(a.size());
    <font color="#0000ff">while</font>(x.hasPrevious())
      System.out.print(x.previous() + " ");
    System.out.println();
    System.out.println("testVisual finished");
  }
  <font color="#009900">// There are some things that only</font>
  <font color="#009900">// LinkedLists can do:</font>
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> testLinkedList() {
    LinkedList ll = <font color="#0000ff">new</font> LinkedList();
    Collection1.fill(ll, 5);
    print(ll);
    <font color="#009900">// Treat it like a stack, pushing:</font>
    ll.addFirst("one");
    ll.addFirst("two");
    print(ll);
    <font color="#009900">// Like "peeking" at the top of a stack:</font>
    System.out.println(ll.getFirst());
    <font color="#009900">// Like popping a stack:</font>
    System.out.println(ll.removeFirst());
    System.out.println(ll.removeFirst());
    <font color="#009900">// Treat it like a queue, pulling elements</font>
    <font color="#009900">// off the tail end:</font>
    System.out.println(ll.removeLast());
    <font color="#009900">// With the above operations, it's a dequeue!</font>
    print(ll);
  }
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String args[]) {
    <font color="#009900">// Make and fill a new list each time:</font>
    basicTest(fill(<font color="#0000ff">new</font> LinkedList()));
    basicTest(fill(<font color="#0000ff">new</font> ArrayList()));
    iterMotion(fill(<font color="#0000ff">new</font> LinkedList()));
    iterMotion(fill(<font color="#0000ff">new</font> ArrayList()));
    iterManipulation(fill(<font color="#0000ff">new</font> LinkedList()));
    iterManipulation(fill(<font color="#0000ff">new</font> ArrayList()));
    testVisual(fill(<font color="#0000ff">new</font> LinkedList()));
    testLinkedList();
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">In
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>basicTest(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>iterMotion(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
the calls are simply made to show the proper syntax, and while the return value
is captured, it is not used. In some cases, the return value isn&#8217;t
captured since it isn&#8217;t typically used. You should look up the full usage
of each of these methods in your online documentation before you use them.
</FONT><a name="_Toc408018580"></a><P></DIV>
<A NAME="Heading265"></A><H3 ALIGN=LEFT>
Using
Sets
<P><A NAME="Index855"></A></H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
has exactly the same interface as 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Collection</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
so there isn&#8217;t any extra functionality as there is with the two different 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s.
Instead, the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is exactly a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Collection</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
it just has different behavior. (This is the ideal use of inheritance and
polymorphism: to express different behavior.) A 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
allows only one instance of each object value to exist (what constitutes the
&#8220;value&#8221; of an object is more complex, as you shall see).
</FONT><P></DIV>
<DIV ALIGN=LEFT><TABLE BORDER>
<COLGROUP>
      <COL width="58">
      <COL width="279">
</COLGROUP>
<TR VALIGN="TOP">
<TD WIDTH=58 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">(interface)</FONT><P></DIV>
</TD>
<TD WIDTH=279 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Each
element that you add to the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
must be unique; otherwise the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
doesn&#8217;t add the duplicate element. Objects added to a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
must define 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>equals(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
to establish object uniqueness. 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
has exactly the same interface as 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Collection</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
A 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
does not guarantee it will maintain its elements in any particular order.
</FONT><P></DIV>
</TD>
</TR>
<A NAME="Index856"></A><TR VALIGN="TOP">
<TD WIDTH=58 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>HashSet*</B></FONT><P></DIV>
</TD>
<TD WIDTH=279 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">For
all 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s
except very small ones. Objects must also define <A NAME="Index857"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>hashCode(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><P></DIV>
</TD>
</TR>
<A NAME="Index858"></A><TR VALIGN="TOP">
<TD WIDTH=58 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ArraySet</B></FONT><P></DIV>
</TD>
<TD WIDTH=279 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">A
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">backed
by an array. Designed for very small 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s,
especially those that are frequently created and destroyed. For small 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s,
creation and iteration is substantially cheaper than for 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>HashSet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Performance
gets quite bad when the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is large. 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>HashCode(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is not required.
</FONT><P></DIV>
</TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH=58 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>TreeSet</B></FONT><P></DIV>
</TD>
<TD WIDTH=279 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">An
ordered 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
backed by a red-black tree.
</FONT><A NAME="fnB38" HREF="#fn38">[38]</A><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
This way, you can extract an ordered sequence from a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><P></DIV>
</TD>
</TR>
</TABLE></DIV>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
following example does 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>not</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
show everything you can do with a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
since the interface is the same as 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Collection</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and so was exercised in the previous example. Instead, this demonstrates the
behavior that makes a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
unique:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: Set1.java</font>
<font color="#009900">// Things you can do with Sets</font>
<font color="#0000ff">package</font> c08.newcollections;
<font color="#0000ff">import</font> java.util.*;

<font color="#0000ff">public</font> <font color="#0000ff">class</font> Set1 {
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> testVisual(Set a) {
    Collection1.fill(a);
    Collection1.fill(a);
    Collection1.fill(a);
    Collection1.print(a); <font color="#009900">// No duplicates!</font>
    <font color="#009900">// Add another set to this one:</font>
    a.addAll(a);
    a.add("one"); 
    a.add("one"); 
    a.add("one");
    Collection1.print(a);
    <font color="#009900">// Look something up:</font>
    System.out.println("a.contains(\"one\"): " +
      a.contains("one"));
  }
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    testVisual(<font color="#0000ff">new</font> HashSet());
    testVisual(<font color="#0000ff">new</font> ArraySet());
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Duplicate
values are added to the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
but when it is printed you&#8217;ll see the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
has accepted only one instance of each value.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">When
you run this program you&#8217;ll notice that the order maintained by the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>HashSet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is different from 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ArraySet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
since each has a different way of storing elements so they can be located
later. (
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ArraySet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
keeps them sorted, while 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>HashSet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
uses a hashing function, which is designed specifically for rapid lookups.)
When creating your own types, be aware that a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Set</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
needs a way to maintain a storage order, just as with the
&#8220;groundhog&#8221; examples shown earlier in this chapter. Here&#8217;s an
example:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: Set2.java</font>
<font color="#009900">// Putting your own type in a Set</font>
<font color="#0000ff">package</font> c08.newcollections;
<font color="#0000ff">import</font>