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<document>
<properties>
<title>BCEL FAQ</title>
</properties>
<body>
<section name="FAQ">
<p>
<b>Q: </b>How can I ... with BCEL?
<br/>
<b>A: </b>Take a look at
<tt>org.apache.bcel.util.BCELifier</tt>, it takes a given class
and converts it to a BCEL program (in Java, of course). It will
show you how certain code is generated using BCEL.
</p>
<p>
<b>Q: </b> Is the BCEL thread-safe?
<br/>
<b>A: </b>BCEL was (deliberately) not designed for thread
safety. See <a href="http://java.sun.com/docs/books/cp/">
"Concurrent Programming in Java"</a>, by Doug Lea,
for an excellent reference on how to build thread-safe wrappers.
</p>
<p>
<b>Q: </b> Can I use BCEL in a commercial product?
<br/>
<b>A: </b> Yes, this is covered by the <a
href="http://www.apache.org/licenses/">Apache License</a>, if you add a note about the original
author and where to find the sources, i.e.,
<a href="http://commons.apache.org/bcel/">http://commons.apache.org/bcel/</a>
</p>
<p>
<b>Q: </b> (Typically for users of Xalan (XSLTC)) I'm getting
<pre>
ClassGenException: Branch target offset too large for short
</pre>
when compiling large files.
<br/>
<b>A: </b> The answer lies in internal limitations of the JVM,
branch instruction like goto can not address offsets larger than
a short integer, i.e. offsets >= 32767.<br/>
The solution is to split the branch into in intermediate hops,
which the XSLTC obviously doesn't take care off.
(In fact you could replace gotos with the goto_w instruction,
but this wouldn't help in the other cases).
</p>
<p>
<b>Q:</b> Can I create or modify classes dynamically with BCEL?
<br/>
<b>A:</b> BCEL contains useful classes in the
<tt>util</tt> package, namely <tt>ClassLoader</tt> and
<tt>JavaWrapper</tt>. Take a look at the <tt> ProxyCreator</tt> example.
</p>
<p>
<b>Q:</b> I get a verification error, what can I do?
<br/>
<b>A:</b> Use the JustIce verifier that comes together with BCEL
to get more detailed information:
<pre>
java org.apache.bcel.verifier.Verifier <your class></pre>
</p>
</section>
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