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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
<title>OpenJava : Tutorial</title>
<meta http-equiv="Keywords" content="java, openjava, reflection">
</head>
<body bgcolor="white"
text="#000000" link="#007fff" vlink="#006fdf" alink="#ff0000">
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<center>
<h1><font color="Blue">OpenJava Tutorial</font></h1>
</center>
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<hr width="100%">
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<h2>5. <font color="blue">Automatic Methods Implementation</font></h2>
<p>In this section, an example of simple translation at <i>callee-side</i>
is described.
<p>The callee-side of a class is whole the declration source code of the
class. Metaprogram in the metaclass for that class (base class)
introspects that class definition in <code>this</code> class object
through the inheriting <code>OJClass</code> interface.
<p>Imagine an utility metaclass which automatically implements
empty methods in its base classes according to their interfaces.
<h3>5.1. What the base-level program should look like</h3>
<p>A base class <code>QuickTest</code> has to implement an interface
<code>java.awt.event.WindowListener</code>, which has several methods
to have to be implemented, but we want to make most of these methods
to have empty body, i.e. do nothing.
<br><blockquote><pre><font color=darkblue>
import java.awt.event.*;
public class <font color=black>QuickTest</font> <b>instantiates <font color=black>AutoImplementerClass</font></b>
implements <font color=black>WindowListener</font>
{
public <font color=black>void</font> windowClosed( <font color=black>WindowEvent</font> e ) { <font color=black>System</font>.exit( 0 ); }
}
</font></pre></blockquote>
<h3>5.2. What the base-level program should be translated</h3>
<p>Like following:
<br><blockquote><pre><font color=darkblue>
public class <font color=black>QuickTest</font> instantiates <font color=black>AutoImplementerClass</font>
implements <font color=black>WindowListener</font>
{
public <font color=black>void</font> windowClosed( <font color=black>WindowEvent</font> e ) { <font color=black>System</font>.exit( 0 ); }
<b>public <font color=black>void</font> windowIconified( <font color=black>WindowEvent</font> e ) { return; }</b>
<b>public <font color=black>void</font> windowDeactivated( <font color=black>WindowEvent</font> e ) { return; }</b>
....
}
</font></pre></blockquote>
<h3>5.3. Write a meta-level program</h3>
<p>So.
<br><blockquote><pre><font color=darkblue>
import io.devnulllabs.openjava.mop.*;
import io.devnulllabs.openjava.ptree.*;
import io.devnulllabs.openjava.syntax.*;
public class AutoImplementerClass instantiates Metaclass extends OJClass
{
public void translateDefinition() throws MOPException {
OJMethod[] methods = getInheritedMethods();
for (int i = 0; i < methods.length; ++i) {
if (! methods[i].getModifiers().isAbstract()
|| methods[i].getReturnType() != OJSystem.VOID
|| hasDeclaredMethod( methods[i] )) continue;
addMethod( makeEmptyMethod( methods[i] ) );
}
}
....
}
</font></pre></blockquote>
<br><blockquote><pre><font color=darkblue>
private boolean hasDeclaredMethod( OJMethod m ) {
try {
getDeclaredMethod( m.getName(), m.getParameterTypes() );
return true;
} catch ( NoSuchMemberException e ) {
return false;
}
}
</font></pre></blockquote>
<br><blockquote><pre><font color=darkblue>
private OJMethod makeEmptyMethod( OJMethod m ) throws MOPException {
/* generates a new method without body */
return new OJMethod( this,
m.getModifiers().remove( OJModifier.ABSTRACT ),
m.getReturnType(), m.getName(), m.getParameterTypes(),
m.getExceptionTypes(),
new StatementList( new ReturnStatement() )
);
}
</font></pre></blockquote>
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<hr width="100%">
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<center>
Please send any message to :
<address>
mich@acm.org
</address><BR>
</center>
<font size=1>Copyright (C) 1999 by Michaki Tatsubori.</font><br>
<font size=1>Java(TM) is a trademark of Sun Microsystems, Inc.</font>
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</body>
</html>
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