tij0122.html

学习java的经典书籍

    }
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Class</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
methods <A NAME="Index1428"></A><A NAME="Index1429"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>getMethods(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and <A NAME="Index1430"></A><A NAME="Index1431"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>getConstructors(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
return an array of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Method</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Constructor</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
respectively. Each of these classes has further methods to dissect the names,
arguments, and return values of the methods they represent. But you can also
just use 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>toString(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
as is done here, to produce a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
with the entire method signature. The rest of the code is just for extracting
command line information, determining if a particular signature matches with
your target string (using <A NAME="Index1432"></A><A NAME="Index1433"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>indexOf(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">),
and printing the results.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
shows reflection in action, since the result produced by 
</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">
cannot be known at compile-time, and therefore all the method signature
information is being extracted at run-time. If you investigate your online
documentation on reflection, you&#8217;ll see that there is enough support to
actually set up and make a method call on an object that&#8217;s totally
unknown at compile-time. Again, this is something you&#8217;ll probably never
need to do yourself &#8211; the support is there for Java and so a programming
environment can manipulate Java Beans &#8211; but it&#8217;s interesting.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">An
interesting experiment is to run 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>java
ShowMethods ShowMethods
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
This produces a listing that includes a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>public</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
default constructor, even though you can see from the code that no constructor
was defined. The constructor you see is the one that&#8217;s automatically
synthesized by the compiler. If you then make 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ShowMethods</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
a non-
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>public</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
class (that is, friendly), the synthesized default constructor no longer shows
up in the output. The synthesized default constructor is automatically given
the same access as the class.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
output for 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ShowMethods</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is still a little tedious. For example, here&#8217;s a portion of the output
produced by invoking 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>java
ShowMethods java.lang.String
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">:</FONT><P></DIV>

<font color="#990000"><PRE><font color="#0000ff">public</font> <font color="#0000ff">boolean</font> 
  java.lang.String.startsWith(java.lang.String,<font color="#0000ff">int</font>)
<font color="#0000ff">public</font> <font color="#0000ff">boolean</font> 
  java.lang.String.startsWith(java.lang.String)
<font color="#0000ff">public</font> <font color="#0000ff">boolean</font> </TT><P><TT><FONT FACE="Courier New" SIZE=3 COLOR="Black">  java.lang.String.endsWith(java.lang.String) </PRE></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">It
would be even nicer if the qualifiers like 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>java.lang</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
could be stripped off. The <A NAME="Index1434"></A><A NAME="Index1435"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StreamTokenizer</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
class introduced in the previous chapter can help solve this problem:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: ShowMethodsClean.java</font>
<font color="#009900">// ShowMethods with the qualifiers stripped</font>
<font color="#009900">// to make the results easier to read</font>
<font color="#0000ff">import</font> java.lang.reflect.*;
<font color="#0000ff">import</font> java.io.*;

<font color="#0000ff">public</font> <font color="#0000ff">class</font> ShowMethodsClean {
  <font color="#0000ff">static</font> <font color="#0000ff">final</font> String usage =
    "usage: \n" +
    "ShowMethodsClean qualified.<font color="#0000ff">class</font>.name\n" +
    "To show all methods in <font color="#0000ff">class</font> or: \n" +
    "ShowMethodsClean qualif.<font color="#0000ff">class</font>.name word\n" +
    "To search <font color="#0000ff">for</font> methods involving 'word'";
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    <font color="#0000ff">if</font>(args.length &lt; 1) {
      System.out.println(usage);
      System.exit(0);
    }
    <font color="#0000ff">try</font> {
      Class c = Class.forName(args[0]);
      Method[] m = c.getMethods();
      Constructor[] ctor = c.getConstructors();
      <font color="#009900">// Convert to an array of cleaned Strings:</font>
      String[] n = 
        <font color="#0000ff">new</font> String[m.length + ctor.length];
      <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; m.length; i++) {
        String s = m[i].toString();
        n[i] = StripQualifiers.strip(s);
      }
      <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; ctor.length; i++) {
        String s = ctor[i].toString();
        n[i + m.length] = 
          StripQualifiers.strip(s);
      }
      <font color="#0000ff">if</font>(args.length == 1)
        <font color="#0000ff">for</font> (<font color="#0000ff">int</font> i = 0; i &lt; n.length; i++)
          System.out.println(n[i]);
      <font color="#0000ff">else</font>
        <font color="#0000ff">for</font> (<font color="#0000ff">int</font> i = 0; i &lt; n.length; i++)
          <font color="#0000ff">if</font>(n[i].indexOf(args[1])!= -1)
            System.out.println(n[i]);
    } <font color="#0000ff">catch</font> (ClassNotFoundException e) {
      System.out.println("No such <font color="#0000ff">class</font>: " + e);
    }
  }
}

<font color="#0000ff">class</font> StripQualifiers {
  <font color="#0000ff">private</font> StreamTokenizer st;
  <font color="#0000ff">public</font> StripQualifiers(String qualified) {
      st = <font color="#0000ff">new</font> StreamTokenizer(
        <font color="#0000ff">new</font> StringReader(qualified));
      st.ordinaryChar(' '); <font color="#009900">// Keep the spaces</font>
  }
  <font color="#0000ff">public</font> String getNext() {
    String s = <font color="#0000ff">null</font>;
    <font color="#0000ff">try</font> {
      <font color="#0000ff">if</font>(st.nextToken() !=
            StreamTokenizer.TT_EOF) {
        <font color="#0000ff">switch</font>(st.ttype) {
          <font color="#0000ff">case</font> StreamTokenizer.TT_EOL:
            s = <font color="#0000ff">null</font>;
            <font color="#0000ff">break</font>;
          <font color="#0000ff">case</font> StreamTokenizer.TT_NUMBER:
            s = Double.toString(st.nval);
            <font color="#0000ff">break</font>;
          <font color="#0000ff">case</font> StreamTokenizer.TT_WORD:
            s = <font color="#0000ff">new</font> String(st.sval);
            <font color="#0000ff">break</font>;
          <font color="#0000ff">default</font>: <font color="#009900">// single character in ttype</font>
            s = String.valueOf((<font color="#0000ff">char</font>)st.ttype);
        }
      }
    } <font color="#0000ff">catch</font>(IOException e) {
      System.out.println(e);
    }
    <font color="#0000ff">return</font> s;
  }
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> String strip(String qualified) {
    StripQualifiers sq = 
      <font color="#0000ff">new</font> StripQualifiers(qualified);
    String s = "", si;
    <font color="#0000ff">while</font>((si = sq.getNext()) != <font color="#0000ff">null</font>) {
      <font color="#0000ff">int</font> lastDot = si.lastIndexOf('.');
      <font color="#0000ff">if</font>(lastDot != -1)
        si = si.substring(lastDot + 1);
      s += si;
    }
    <font color="#0000ff">return</font> s;
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
class 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ShowMethodsClean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is quite similar to the previous 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>ShowMethods</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
except that it takes the arrays of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Method</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Constructor</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and converts them into a single array of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
Each of these 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects is then passed through
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>
StripQualifiers.Strip(&#160;)
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
to remove all the method qualification. As you can see, this uses the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StreamTokenizer</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
manipulation to do its work.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
tool can be a real time-saver while you&#8217;re programming, when you
can&#8217;t remember if a class has a particular method and you don&#8217;t
want to go walking through the class hierarchy in the online documentation, or
if you don&#8217;t know whether that class can do anything with, for example, 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Color</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Chapter
17 contains a GUI version of this program so you can leave it running while
you&#8217;re writing code, to allow quick lookups.
</FONT><a name="_Toc408018651"></a><a name="_Toc375545411"></a><P></DIV>

<div align="right">
<a href="tij_c.html">Contents</a> | <a href="tij0121.html">Prev</a> | <a href="tij0123.html">Next</a>
</div>
</body></html>