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POIs it possible for the same javac compiler to compile the same set of source files but produce class files of different checksums?
 

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  1. POIs it possible for the same javac compiler to compile the same set of source files but produce class files of different checksums?
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    <p>I was attempting to compare the results of this: (in ant)</p> <pre><code> &lt;javac target="1.5" source="1.5" deprecation="on" fork="yes" optimize="true" debug="true" debuglevel="lines,vars,source"&gt; &lt;classpath&gt; &lt;fileset dir="${project.basedir}/../lib"&gt; &lt;include name="**/*.jar" /&gt; &lt;include name="**/*.zip" /&gt; &lt;/fileset&gt; &lt;/classpath&gt; &lt;/javac&gt; </code></pre> <p>...against this: (in maven)</p> <pre><code> &lt;plugin&gt; &lt;artifactId&gt;maven-compiler-plugin&lt;/artifactId&gt; &lt;version&gt;2.3.2&lt;/version&gt; &lt;executions&gt; &lt;execution&gt; &lt;id&gt;compile&lt;/id&gt; &lt;phase&gt;compile&lt;/phase&gt; &lt;goals&gt; &lt;goal&gt;compile&lt;/goal&gt; &lt;/goals&gt; &lt;configuration&gt; &lt;target&gt;1.5&lt;/target&gt; &lt;source&gt;1.5&lt;/source&gt; &lt;debug&gt;true&lt;/debug&gt; &lt;debuglevel&gt;lines,vars,source&lt;/debuglevel&gt; &lt;showDeprecation&gt;true&lt;/showDeprecation&gt; &lt;optimize&gt;true&lt;/optimize&gt; &lt;fork&gt;true&lt;/fork&gt; &lt;includes&gt; ... &lt;/includes&gt; &lt;/configuration&gt; &lt;/execution&gt; &lt;/executions&gt; &lt;/plugin&gt; </code></pre> <p>...only to discover that 2 of the resulting class files have slightly different checksums, while the rest are identical. I consider multi-threading to have played a part, but the checksums produced for either option appear to be consistent upon repeated attempts. What can possibly account for this result? </p> <p><strong>Update:</strong></p> <p>I have examined one set of the files with different checksums using <code>javap -verbose</code> and noticed the only difference being:</p> <pre><code>const #16 = class #108; // java/lang/Exception const #17 = Method #102.#109; // java/io/Writer.close:()V const #18 = Method #7.#109; // java/io/FileWriter.close:()V </code></pre> <p>as opposed to:</p> <pre><code>const #16 = Method #102.#108; // java/io/Writer.close:()V const #17 = Method #7.#108; // java/io/FileWriter.close:()V const #18 = class #109; // java/lang/Exception </code></pre>
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    1. COHave you tried comparing the contents of the files?
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    2. CO@delnan I did, using javap
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    3. COI would: (1) make sure both are picking up exactly the same Java compiler; (2) capture & compare the two sets of options that are passed to the compiler.
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