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<?xml version="1.0" encoding="UTF-8" ?>
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<span class="el_source">FAQ</span>
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<h1>FAQ</h1>
<p>
This is a compilation of questions that have been asked by JaCoCo users
before.
</p>
<h3>Does JaCoCo have a plug-in for [Eclipse|Netbeans|Whatever...]?</h3>
<p>
See <a href="integrations.html">this list</a> for current integrations with
various tools.
</p>
<h3>What Java versions are supported by JaCoCo?</h3>
<p>
JaCoCo supports Java class files from version 1.0 to 1.8. However the minimum
JRE version required by the JaCoCo runtime (e.g. the agent) and the JaCoCo
tools is 1.5. Also note that class files under test from version 1.6 and above
have to contain valid stackmap frames.
</p>
<h3>Why do I get the error "Can't add different class with same name"?</h3>
<p>
For coverage report generation all classes within a group must have unique
names. You get this error during report generation if JaCoCo is supplied with
multiple different class files with the same name. To fix this remove those
duplicate classes or create separate reports or report groups for each version.
</p>
<h3>Code with exceptions shows no coverage. Why?</h3>
<p>
JaCoCo determines code execution with so called probes. Probes are inserted
into the control flow at certain positions. Code is considered as executed
when a subsequent probe has been executed. In case of exceptions such a
sequence of instructions is aborted somewhere in the middle and not marked as
executed.
</p>
<h3>Why does the coverage report not show line coverage figures?</h3>
<p>
JaCoCo is based on class files analysis. To calculate line coverage class
files must contain line number attributes. For this your code must be compiled
with debug information.
</p>
<h3>Why does the coverage report not show highlighted source code?</h3>
<p>
Make sure the following prerequisites are fulfilled to get source code
highlighting in JaCoCo coverage reports:
</p>
<ul>
<li>Class files must be compiled with debug information to contain line numbers.</li>
<li>Source files must be properly supplied at report generation time. I.e.
specified source folders must be the direct parent of the folders that
define the Java packages.</li>
</ul>
<h3>Why does a class show as not covered although it has been executed?</h3>
<p>
First make sure execution data has been collected. For this select the
<i>Sessions</i> link on the top right corner of the HTML report and check
whether the class in question is listed. If it is listed but not linked the
class at execution time is a different class file. Make sure you're using the
exact same class file at runtime as for report generation. Note that some
tools (e.g. EJB containers, mocking frameworks) might modify your class files
at runtime. Please see the chapter about <a href="classids.html"> class
ids</a> for a detailed discussion.
</p>
<h3>Why are Java interface types not shown in the coverage reports?</h3>
<p>
Java interface methods do not contain code, therefore code coverage cannot
be evaluated. Indeed code coverage is recorded for the implementation classes.
The same applies to abstract methods in abstract classes.
</p>
<h3>Can I collect coverage information without stopping the JVM?</h3>
<p>
Yes, there are two possible ways: The JaCoCo <a href="agent.html">agent</a>
can be configured for remote control via TCP/IP sockets. This allows to
collect execution data at any point in time from a running JVM. The
<a href="ant.html#dump"><code>dump</code> Ant task</a> or the
<a href="dump-mojo.html"><code>dump</code> Maven goal</a> can be used to
request dumps. The remote control feature also allows you to reset execution
data.
</p>
<p>
Alternatively the JaCoCo <a href="agent.html">agent</a> can be configured to
expose some functionality via JMX (<code>jmx=true</code>). The bean
<code><a href="./api/org/jacoco/agent/rt/IAgent.html">org.jacoco:type=Runtime</a></code>
provides operations to dump and reset execution data at any point in time.
</p>
<h3>My code uses reflection. Why does it fail when I execute it with JaCoCo?</h3>
<p>
To collect execution data JaCoCo instruments the classes under test which adds
two members to the classes: A private static field <code>$jacocoData</code>
and a private static method <code>$jacocoInit()</code>. Both members are
marked as synthetic.
</p>
<p>
Please change your code to ignore synthetic members. This is a good practice
anyways as also the Java compiler creates synthetic members in certain
situation.
</p>
<h3>Why do I get an error while instrumenting certain Java classes?</h3>
<p>
JaCoCo can instrument valid class files only. Class files with syntactical or
semantical error will typically lead to exceptions. In certain areas JaCoCo is
more restrictive then the JVM: JaCoCo expects valid so-called "stackmap
frame" information in class files of version 1.6 or higher. In turn JaCoCo
instrumented classes are expected to conform the specification.
</p>
<p>
Invalid class files are typically created by some frameworks which do not
properly adjust stackmap frames when manipulating bytecode.
</p>
<h3>Does JaCoCo run on the IBM JRE J9 and WebSphere?</h3>
<p>
It does. To make the JaCoCo agent work please set the VM option
<code>-Xshareclasses:none</code>.
</p>
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