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example can be rewritten using Java 1.1<A NAME="Index1388"></A>
class literals<A NAME="Index1389"></A><A NAME="Index1390"></A>.
The result is cleaner in many ways:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: PetCount2.java</font>
<font color="#009900">// Using Java 1.1 class literals</font>
<font color="#0000ff">package</font> c11.petcount2;
<font color="#0000ff">import</font> java.util.*;

<font color="#0000ff">class</font> Pet {}
<font color="#0000ff">class</font> Dog <font color="#0000ff">extends</font> Pet {}
<font color="#0000ff">class</font> Pug <font color="#0000ff">extends</font> Dog {}
<font color="#0000ff">class</font> Cat <font color="#0000ff">extends</font> Pet {}
<font color="#0000ff">class</font> Rodent <font color="#0000ff">extends</font> Pet {}
<font color="#0000ff">class</font> Gerbil <font color="#0000ff">extends</font> Rodent {}
<font color="#0000ff">class</font> Hamster <font color="#0000ff">extends</font> Rodent {}

<font color="#0000ff">class</font> Counter { <font color="#0000ff">int</font> i; }

<font color="#0000ff">public</font> <font color="#0000ff">class</font> PetCount2 {
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    Vector pets = <font color="#0000ff">new</font> Vector();
    Class[] petTypes = {
      <font color="#009900">// Class literals work in Java 1.1+ only:</font>
      Pet.<font color="#0000ff">class</font>,
      Dog.<font color="#0000ff">class</font>,
      Pug.<font color="#0000ff">class</font>,
      Cat.<font color="#0000ff">class</font>,
      Rodent.<font color="#0000ff">class</font>,
      Gerbil.<font color="#0000ff">class</font>,
      Hamster.<font color="#0000ff">class</font>,
    };
    <font color="#0000ff">try</font> {
      <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; 15; i++) {
        <font color="#009900">// Offset by one to eliminate Pet.class:</font>
        <font color="#0000ff">int</font> rnd = 1 + (<font color="#0000ff">int</font>)(
          Math.random() * (petTypes.length - 1));
        pets.addElement(
          petTypes[rnd].newInstance());
      }
    } <font color="#0000ff">catch</font>(InstantiationException e) {}
      <font color="#0000ff">catch</font>(IllegalAccessException e) {}
    Hashtable h = <font color="#0000ff">new</font> Hashtable();
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; petTypes.length; i++)
      h.put(petTypes[i].toString(),
        <font color="#0000ff">new</font> Counter());
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; pets.size(); i++) {
      Object o = pets.elementAt(i);
      <font color="#0000ff">if</font>(o <font color="#0000ff">instanceof</font> Pet)
        ((Counter)h.get(
          "<font color="#0000ff">class</font> c11.petcount2.Pet")).i++;
      <font color="#0000ff">if</font>(o <font color="#0000ff">instanceof</font> Dog)
        ((Counter)h.get(
          "<font color="#0000ff">class</font> c11.petcount2.Dog")).i++;
      <font color="#0000ff">if</font>(o <font color="#0000ff">instanceof</font> Pug)
        ((Counter)h.get(
          "<font color="#0000ff">class</font> c11.petcount2.Pug")).i++;
      <font color="#0000ff">if</font>(o <font color="#0000ff">instanceof</font> Cat)
        ((Counter)h.get(
          "<font color="#0000ff">class</font> c11.petcount2.Cat")).i++;
      <font color="#0000ff">if</font>(o <font color="#0000ff">instanceof</font> Rodent)
        ((Counter)h.get(
          "<font color="#0000ff">class</font> c11.petcount2.Rodent")).i++;
      <font color="#0000ff">if</font>(o <font color="#0000ff">instanceof</font> Gerbil)
        ((Counter)h.get(
          "<font color="#0000ff">class</font> c11.petcount2.Gerbil")).i++;
      <font color="#0000ff">if</font>(o <font color="#0000ff">instanceof</font> Hamster)
        ((Counter)h.get(
          "<font color="#0000ff">class</font> c11.petcount2.Hamster")).i++;
    }
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; pets.size(); i++)
      System.out.println(
        pets.elementAt(i).getClass().toString());
    Enumeration keys = h.keys();
    <font color="#0000ff">while</font>(keys.hasMoreElements()) {
      String nm = (String)keys.nextElement();
      Counter cnt = (Counter)h.get(nm);
      System.out.println(
        nm.substring(nm.lastIndexOf('.') + 1) + 
        " quantity: " + cnt.i);
    }
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Here,
the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>typenames</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
array has been removed in favor of getting the type name strings from the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Class</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
object. Notice the extra work for this: the class name is not, for example, 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Gerbil,</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
but instead 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>c11.petcount2.Gerbil</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
since the package name is included. Notice also that the system can distinguish
between classes and interfaces.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">You
can also see that the creation of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>petTypes</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
does not need to be surrounded by a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>try</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
block since it&#8217;s evaluated at compile time and thus won&#8217;t throw any
exceptions, unlike 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Class.forName(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">When
the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Pet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects are dynamically created, you can see that the random number is
restricted so it is between 1 and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>petTypes.length</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and does not include zero. That&#8217;s because zero refers to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Pet.class</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
and presumably a generic 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Pet</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
object is not interesting. However, since 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Pet.class</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is part of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>petTypes</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
the result is that all of the pets get counted.
</FONT><P></DIV>
<A NAME="Heading358"></A><H4 ALIGN=LEFT>
A
dynamic instanceof
<P><A NAME="Index1391"></A></H4>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Java
1.1<A NAME="Index1392"></A>
has added the <A NAME="Index1393"></A><A NAME="Index1394"></A><A NAME="Index1395"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>isInstance</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
method to the class 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Class</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
This allows you to dynamically call the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>instanceof</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
operator, which you could do only statically in Java 1.0<A NAME="Index1396"></A>
(as previously shown). Thus, all those tedious 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>instanceof</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
statements can be removed in the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PetCount</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
example:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: PetCount3.java</font>
<font color="#009900">// Using Java 1.1 isInstance()</font>
<font color="#0000ff">package</font> c11.petcount3;
<font color="#0000ff">import</font> java.util.*;

<font color="#0000ff">class</font> Pet {}
<font color="#0000ff">class</font> Dog <font color="#0000ff">extends</font> Pet {}
<font color="#0000ff">class</font> Pug <font color="#0000ff">extends</font> Dog {}
<font color="#0000ff">class</font> Cat <font color="#0000ff">extends</font> Pet {}
<font color="#0000ff">class</font> Rodent <font color="#0000ff">extends</font> Pet {}
<font color="#0000ff">class</font> Gerbil <font color="#0000ff">extends</font> Rodent {}
<font color="#0000ff">class</font> Hamster <font color="#0000ff">extends</font> Rodent {}

<font color="#0000ff">class</font> Counter { <font color="#0000ff">int</font> i; }

<font color="#0000ff">public</font> <font color="#0000ff">class</font> PetCount3 {
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    Vector pets = <font color="#0000ff">new</font> Vector();
    Class[] petTypes = {
      Pet.<font color="#0000ff">class</font>,
      Dog.<font color="#0000ff">class</font>,
      Pug.<font color="#0000ff">class</font>,
      Cat.<font color="#0000ff">class</font>,
      Rodent.<font color="#0000ff">class</font>,
      Gerbil.<font color="#0000ff">class</font>,
      Hamster.<font color="#0000ff">class</font>,
    };
    <font color="#0000ff">try</font> {
      <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; 15; i++) {
        <font color="#009900">// Offset by one to eliminate Pet.class:</font>
        <font color="#0000ff">int</font> rnd = 1 + (<font color="#0000ff">int</font>)(
          Math.random() * (petTypes.length - 1));
        pets.addElement(
          petTypes[rnd].newInstance());
      }
    } <font color="#0000ff">catch</font>(InstantiationException e) {}
      <font color="#0000ff">catch</font>(IllegalAccessException e) {}
    Hashtable h = <font color="#0000ff">new</font> Hashtable();
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; petTypes.length; i++)
      h.put(petTypes[i].toString(),
        <font color="#0000ff">new</font> Counter());
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; pets.size(); i++) {
      Object o = pets.elementAt(i);
      <font color="#009900">// Using isInstance to eliminate individual</font>
      <font color="#009900">// instanceof expressions:</font>
      <font color="#0000ff">for</font> (<font color="#0000ff">int</font> j = 0; j &lt; petTypes.length; ++j)
        <font color="#0000ff">if</font> (petTypes[j].isInstance(o)) {
          String key = petTypes[j].toString();
          ((Counter)h.get(key)).i++;
        }
    }
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; pets.size(); i++)
      System.out.println(
        pets.elementAt(i).getClass().toString());
    Enumeration keys = h.keys();
    <font color="#0000ff">while</font>(keys.hasMoreElements()) {
      String nm = (String)keys.nextElement();
      Counter cnt = (Counter)h.get(nm);
      System.out.println(
        nm.substring(nm.lastIndexOf('.') + 1) + 
        " quantity: " + cnt.i);
    }
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">You
can see that the Java 1.1<A NAME="Index1397"></A>
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>isInstance(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
method has eliminated the need for the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>instanceof</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
expressions. In addition, this means that you can add new types of pets simply
by changing the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>petTypes</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
array; the rest of the program does not need modification (as it did when using
the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>instanceof</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
expressions).
</FONT><a name="_Toc375545407"></a><a name="_Toc408018648"></a><a name="_Toc305593313"></a><a name="_Toc305628785"></a><a name="_Toc312374146"></a><a name="_Toc375545409"></a><P></DIV>

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