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<div class="section" id="redefine">
<span id="redefine"></span><h1>redefine<a class="headerlink" href="#redefine" title="Permalink to this headline">¶</a></h1>
<blockquote>
<div>Load the external <tt class="docutils literal">*.class</tt> files to re-define the loaded peer class in JVM.</div></blockquote>
<p>Reference: <a class="reference external" href="https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/Instrumentation.html#redefineClasses-java.lang.instrument.ClassDefinition...-">Instrumentation#redefineClasses</a></p>
<blockquote>
<div>Notes: Re-defined classes cannot be restored. There are chances that redefining may fail due to some reasons, for example: there’s new field introduced in the new version of the class, pls. refer to JDK’s documentation for the limitations.</div></blockquote>
<div class="section" id="options">
<span id="options"></span><h2>Options<a class="headerlink" href="#options" title="Permalink to this headline">¶</a></h2>
<table border="1" class="docutils">
<thead>
<tr>
<th align="right">Name</th>
<th align="left">Specification</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right"><code>[c:]</code></td>
<td align="left">hashcode of the class loader</td>
</tr>
<tr>
<td align="right"><code>[p:]</code></td>
<td align="left">absolute path of the external <code>*.class</code>, multiple paths are separated with 'space'</td>
</tr>
</tbody>
</table></div>
<div class="section" id="usage">
<span id="usage"></span><h2>Usage<a class="headerlink" href="#usage" title="Permalink to this headline">¶</a></h2>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">redefine -p /tmp/Test.class
redefine -c 327a647b -p /tmp/Test.class /tmp/Test$Inner.class
</pre></div>
</div>
</div>
<div class="section" id="restrictions-of-the-redefine-command">
<span id="restrictions-of-the-redefine-command"></span><h2>Restrictions of the redefine command<a class="headerlink" href="#restrictions-of-the-redefine-command" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">New field/method is not allowed</p>
</li>
<li><p class="first">The function that is running, no exit can not take effect, such as the new <tt class="docutils literal">System.out.println</tt> added below, only the <tt class="docutils literal">run()</tt> function will take effect.</p>
<div class="highlight-java notranslate"><div class="highlight hljs"><pre class="java">public class MathGame {
public static void main(String[] args) throws InterruptedException {
MathGame game = new MathGame();
while (true) {
game.run();
TimeUnit.SECONDS.sleep(1);
// This doesn't work because the code keeps running in while
System.out.println("in loop");
}
}
public void run() throws InterruptedException {
// This works because the run() function ends completely every time
System.out.println("call run()");
try {
int number = random.nextInt();
List<Integer> primeFactors = primeFactors(number);
print(number, primeFactors);
} catch (Exception e) {
System.out.println(String.format("illegalArgumentCount:%3d, ", illegalArgumentCount) + e.getMessage());
}
}
</pre></div>
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</li>
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<div class="highlight-default notranslate"><pre class="literal-block"></pre>
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