tij0093.html

学习java的经典书籍

</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Hashtable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
are 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>not</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
included because in all cases there are preferred classes within the new
collections.
</FONT><a name="_Toc408018579"></a><P></DIV>
<A NAME="Heading264"></A><H3 ALIGN=LEFT>
Using
Lists
</H3>
<DIV ALIGN=LEFT><TABLE BORDER>
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<TD WIDTH=63 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
(interface)
</FONT><P></DIV>
</TD>
<TD WIDTH=265 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Order
is the most important feature of a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">;
it promises to maintain elements in a particular sequence. <A NAME="Index851"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
adds a number of methods to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Collection</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
that allow
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">insertion
and removal of elements in the middle of a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List.
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">(This
is recommended only for a <A NAME="Index852"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>LinkedList.</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">A
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">will
produce a <A NAME="Index853"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ListIterator</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
and using this you can traverse the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
in both directions, as well as insert and remove elements in the middle of the
list (again, recommended only for a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>LinkedList</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">).</FONT><P></DIV>
</TD>
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<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ArrayList*</B></FONT><P></DIV>
</TD>
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<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">A
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">backed
by an array. Use instead of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
as a general-purpose object holder. Allows rapid random access to elements, but
is slow when inserting and removing elements from the middle of a list. 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ListIterator</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
should be used only for back-and-forth traversal of an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ArrayList</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
but not for inserting and removing elements, which is expensive compared to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>LinkedList</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><P></DIV>
</TD>
</TR>
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<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>LinkedList</B></FONT><P></DIV>
</TD>
<TD WIDTH=265 COLSPAN=1 ROWSPAN=1 VALIGN=TOP>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Provides
optimal sequential access, with inexpensive insertions and deletions from the
middle of the list. Relatively slow for random access. (Use 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ArrayList</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
instead.) Also has 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>addFirst(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>addLast(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>getFirst(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>getLast(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>removeFirst(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>removeLast(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
(which are not defined in any interfaces or base classes) to allow it to be
used as a stack, a queue, and a dequeue.
</FONT><P></DIV>
</TD>
</TR>
</TABLE></DIV>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
methods in the following example each cover a different group of activities:
things that every list can do (
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>basicTest(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">),
moving around with an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Iterator</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
(
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>iterMotion(&#160;)</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">versus
changing things with an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Iterator</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
(
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>iterManipulation(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">),
seeing the effects of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>List</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
manipulation (
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>testVisual(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">),
and operations available only to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>LinkedList</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s.</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: List1.java</font>
<font color="#009900">// Things you can do with Lists</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> List1 {
  <font color="#009900">// Wrap Collection1.fill() for convenience:</font>
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> List fill(List a) {
    <font color="#0000ff">return</font> (List)Collection1.fill(a);
  }
  <font color="#009900">// You can use an Iterator, just as with a</font>
  <font color="#009900">// Collection, but you can also use random</font>
  <font color="#009900">// access with get():</font>
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> print(List a) {
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; a.size(); i++)
      System.out.print(a.get(i) + " ");
    System.out.println();
  }
  <font color="#0000ff">static</font> <font color="#0000ff">boolean</font> b;
  <font color="#0000ff">static</font> Object o;
  <font color="#0000ff">static</font> <font color="#0000ff">int</font> i;
  <font color="#0000ff">static</font> Iterator it;
  <font color="#0000ff">static</font> ListIterator lit;
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> basicTest(List a) {
    a.add(1, "x"); <font color="#009900">// Add at location 1</font>
    a.add("x"); <font color="#009900">// Add at end</font>
    <font color="#009900">// Add a collection:</font>
    a.addAll(fill(<font color="#0000ff">new</font> ArrayList()));
    <font color="#009900">// Add a collection starting at location 3:</font>
    a.addAll(3, fill(<font color="#0000ff">new</font> ArrayList())); 
    b = a.contains("1"); <font color="#009900">// Is it in there?</font>
    <font color="#009900">// Is the entire collection in there?</font>
    b = a.containsAll(fill(<font color="#0000ff">new</font> ArrayList()));
    <font color="#009900">// Lists allow random access, which is cheap</font>
    <font color="#009900">// for ArrayList, expensive for LinkedList:</font>
    o = a.get(1); <font color="#009900">// Get object at location 1</font>
    i = a.indexOf("1"); <font color="#009900">// Tell index of object</font>
    <font color="#009900">// indexOf, starting search at location 2:</font>
    i = a.indexOf("1", 2);
    b = a.isEmpty(); <font color="#009900">// Any elements inside?</font>
    it = a.iterator(); <font color="#009900">// Ordinary Iterator</font>
    lit = a.listIterator(); <font color="#009900">// ListIterator</font>
    lit = a.listIterator(3); <font color="#009900">// Start at loc 3</font>
    i = a.lastIndexOf("1"); <font color="#009900">// Last match </font>
    i = a.lastIndexOf("1", 2); <font color="#009900">// ...after loc 2</font>
    a.remove(1); <font color="#009900">// Remove location 1</font>
    a.remove("3"); <font color="#009900">// Remove this object</font>
    a.set(1, "y"); <font color="#009900">// Set location 1 to "y"</font>
    <font color="#009900">// Make an array from the List:</font>
    Object[] array = a.toArray(); 
    <font color="#009900">// Keep everything that's in the argument</font>
    <font color="#009900">// (the intersection of the two sets):</font>
    a.retainAll(fill(<font color="#0000ff">new</font> ArrayList()));
    <font color="#009900">// Remove elements in this range:</font>
    a.removeRange(0, 2);
    <font color="#009900">// Remove everything that's in the argument:</font>
    a.removeAll(fill(<font color="#0000ff">new</font> ArrayList()));
    i = a.size(); <font color="#009900">// How big is it?</font>
    a.clear(); <font color="#009900">// Remove all elements</font>
  }
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> iterMotion(List a) {
    ListIterator it = a.listIterator();
    b = it.hasNext();
    b = it.hasPrevious();
    o = it.next();
    i = it.nextIndex();
    o = it.previous();
    i = it.previousIndex();
  }
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> iterManipulation(List a) {
    ListIterator it = a.listIterator();
    it.add("47");
    <font color="#009900">// Must move to an element after add():</font>
    it.next();
    <font color="#009900">// Remove the element that was just produced:</font>
    it.remove(); 
    <font color="#009900">// Must move to an element after remove():</font>
    it.next();
    <font color="#009900">// Change the element that was just produced:</font>
    it.set("47");
  }
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> testVisual(List a) {
    print(a);
    List b = <font color="#0000ff">new</font> ArrayList();
    fill(b);
    System.out.print("b = ");
    print(b);
    a.addAll(b);
    a.addAll(fill(<font color="#0000ff">new</font> ArrayList()));
    print(a);
    <font color="#009900">// Shrink the list by removing all the </font>
    <font color="#009900">// elements beyond the first 1/2 of the list</font>
    System.out.println(a.size());
    System.out.println(a.size()/2);
    a.removeRange(a.size()/2, a.size()/2 + 2);
    print(a);
    <font color="#009900">// Insert, remove, and replace elements</font>
    <font color="#009900">// using a ListIterator:</font>
    ListIterator x = a.listIterator(a.size()/2);
    x.add("one"); 
    print(a);
    System.out.println(x.next());
    x.remove();
    System.out.println(x.next());
    x.set("47");
    print(a);
    <font color="#009900">// Traverse the list backwards:</font>