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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">
<!---------------------------------------------------------------------->
<center>
<h1><font color="Blue">OpenJava Tutorial</font></h1>
</center>
<!---------------------------------------------------------------------->
<hr width="100%">
<!---------------------------------------------------------------------->
<h2>6. <font color="blue">Callee-side Translation</font></h2>
<p>In this section, an example of simple translation at <i>callee-side</i>
is described.
<h3>6.1. What the base-level program should look like</h3>
<br><blockquote><pre><font color=darkblue>
import java.util.*;
public class <font color=black>VectorStack</font> <b>instantiates <font color=black>AdapterClass</font></b>
<b>adapts <font color=black>Vector</font> in v to <font color=black>Stack</font></b>
{
<font color=black>Vector</font> v;
public <font color=black>VectorStack</font>( <font color=black>Vector</font> v ) {
this.v = v;
}
public <font color=black>void</font> push( <font color=black>Object</font> o ) {
v.addElement( o );
}
public <font color=black>Object</font> pop() {
<font color=black>Object</font> result = peek();
v.removeElementAt( v.size() - 1 );
return result;
}
public <font color=black>Object</font> peek() {
return v.elementAt( v.size() - 1 );
}
}
</font></pre></blockquote>
<br><blockquote><pre><font color=darkblue>
public interface <font color=black>Stack</font>
{
public <font color=black>int</font> size();
public <font color=black>boolean</font> isEmpty();
public <font color=black>Enumeration</font> elements();
public <font color=black>Object[]</font> toArray();
public <font color=black>int</font> hashCode();
public <font color=black>void</font> push( <font color=black>Object</font> o );
public <font color=black>Object</font> pop();
public <font color=black>Object</font> peek();
}
</font></pre></blockquote>
<h3>6.2. What the base-level program should be translated</h3>
<p>Like following:
<br><blockquote><pre><font color=darkblue>
import java.util.*;
public class <font color=black>VectorStack</font> implements <font color=black>Stack</font>
{
<font color=black>Vector</font> v;
public <font color=black>VectorStack</font>( <font color=black>Vector</font> v ) {
this.v = v;
}
public <font color=black>void</font> push( <font color=black>Object</font> o ) {
v.addElement( o );
}
public <font color=black>Object</font> pop() {
<font color=black>Object</font> result = peek();
v.removeElementAt( v.size() - 1 );
return result;
}
public <font color=black>Object</font> peek() {
return v.elementAt( v.size() - 1 );
}
<b>public <font color=black>Object[]</font> toArray() {</b>
<b>return v.toArray();</b>
<b>}</b>
<b>public <font color=black>int</font> size() {</b>
<b>return v.size();</b>
<b>}</b>
<b>public <font color=black>Enumeration</font> elements() {</b>
<b>return v.elements();</b>
<b>}</b>
<b>public <font color=black>boolean</font> isEmpty() {</b>
<b>return v.isEmpty();</b>
<b>}</b>
<b>public <font color=black>int</font> hashCode() {</b>
<b>return v.hashCode();</b>
<b>}</b>
}
</font></pre></blockquote>
<h3>6.3. Write a meta-level program</h3>
<br><blockquote><pre><font color=darkblue>
import io.devnulllabs.openjava.mop.*;
import io.devnulllabs.openjava.ptree.*;
import io.devnulllabs.openjava.syntax.*;
/**
* The metaclass <code>AdapterClass</code> supports classes
* implementing an adapter role of the Adapter pattern.
* The target's methods with same signatures as the adaptee's are
* automatically implemented into the adapter class.
*/
public class AdapterClass instantiates Metaclass extends OJClass
{
public static final String KEY_ADAPTS = "adapts";
/* overrides for translation */
public void translateDefinition() throws MOPException {
OJClass target = getTarget(), adaptee = getAdaptee();
if (target == null || adaptee == null) return;
/* implicit forwarding to the same signature's */
OJMethod[] adapteds = adaptee.getMethods( this );
for (int i = 0; i < adapteds.length; ++i) {
/* picks up the method with same signature */
OJMethod m;
try {
m = getTarget().getMethod( adapteds[i].getName(),
adapteds[i].getParameterTypes(),
this );
} catch ( NoSuchMemberException e ) { /* not match */ continue; }
/* generate a forwarding method with forwarded's name */
addMethod( makeForwardingMethod( m.getName(), m ) );
}
addInterface( getTarget() );
}
/**
* Generates a forwarding method with specified name.
*
* @param name generating method's name.
* @param forwarded method to which the generated method forwards.
* @return a generated forwarding method.
*/
private OJMethod makeForwardingMethod( String name, OJMethod forwarded )
throws MOPException
{
/* generates a new method without body */
OJMethod result = new OJMethod(
this,
forwarded.getModifiers().remove( OJModifier.ABSTRACT ),
forwarded.getReturnType(),
name,
forwarded.getParameterTypes(),
forwarded.getExceptionTypes(),
null
);
/* generates a method call and return statement */
ExpressionList params = result.getParameterVariables();
Expression expr = new MethodCall( getContainer(), name, params );
StatementList body = new StatementList();
if (forwarded.getReturnType() == OJSystem.VOID) {
body.add( new ExpressionStatement( expr ) );
body.add( new ReturnStatement() );
} else {
body.add( new ReturnStatement( expr ) );
}
result.setBody( body );
return result;
}
/* extended information */
private OJClass getAdaptee() throws MOPException {
ObjectList suffix = (ObjectList) getSuffix( KEY_ADAPTS );
return OJClass.forName( suffix.get( 0 ).toString() );
}
private Variable getContainer() throws MOPException {
ObjectList suffix = (ObjectList) getSuffix( KEY_ADAPTS );
return new Variable( suffix.get( 1 ).toString() );
}
private OJClass getTarget() throws MOPException {
ObjectList suffix = (ObjectList) getSuffix( KEY_ADAPTS );
return OJClass.forName( suffix.get( 2 ).toString() );
}
/* override to extend syntax */
public static boolean isRegisteredKeyword( String keyword ) {
return keyword.equals( KEY_ADAPTS );
}
/* override to extend syntax */
public static SyntaxRule getDeclSuffixRule( String keyword ) {
if (keyword.equals( KEY_ADAPTS )) {
return new CompositeRule(
new TypeNameRule(),
new PrepPhraseRule( "in", new NameRule() ),
new PrepPhraseRule( "to", new TypeNameRule() ) );
}
return null;
}
}
</font></pre></blockquote>
<!---------------------------------------------------------------------->
<hr width="100%">
<!---------------------------------------------------------------------->
<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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