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2013-12-26 19:10:58 +04:00
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2013-03-18 15:50:26 +04:00
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<body>
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<h2>Frequently Asked Questions</h2>
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<h3>Contents</h3>
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<ol>
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<li><a href="#shrinking">What is shrinking?</a></li>
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<li><a href="#obfuscation">What is obfuscation?</a></li>
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<li><a href="#preverification">What is preverification?</a></li>
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<li><a href="#optimization">What kind of optimizations does <b>ProGuard</b>
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support?</a></li>
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<li><a href="#commercial">Can I use <b>ProGuard</b> to process my commercial
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application?</a></li>
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<li><a href="#jdk1.4">Does <b>ProGuard</b> work with Java 2? Java 5? Java
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6? Java 7?</a></li>
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<li><a href="#jme">Does <b>ProGuard</b> work with Java Micro Edition?</a></li>
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<li><a href="#android">Does <b>ProGuard</b> work for Google Android
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code?</a></li>
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<li><a href="#blackberry">Does <b>ProGuard</b> work for Blackberry
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code?</a></li>
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<li><a href="#ant">Does <b>ProGuard</b> have support for Ant?</a></li>
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<li><a href="#gradle">Does <b>ProGuard</b> have support for Gradle?</a></li>
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<li><a href="#maven">Does <b>ProGuard</b> have support for Maven?</a></li>
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<li><a href="#gui">Does <b>ProGuard</b> come with a GUI?</a></li>
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<li><a href="#forname">Does <b>ProGuard</b> handle <code>Class.forName</code>
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calls?</a></li>
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<li><a href="#resource">Does <b>ProGuard</b> handle resource files?</a></li>
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<li><a href="#encrypt">Does <b>ProGuard</b> encrypt string constants?</a></li>
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<li><a href="#flow">Does <b>ProGuard</b> perform control flow
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obfuscation?</a></li>
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<li><a href="#incremental">Does <b>ProGuard</b> support incremental
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obfuscation?</a></li>
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<li><a href="#keywords">Can <b>ProGuard</b> obfuscate using reserved
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keywords?</a></li>
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<li><a href="#stacktrace">Can <b>ProGuard</b> reconstruct obfuscated stack
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traces?</a></li>
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</ol>
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<h3><a name="shrinking">What is shrinking?</a></h3>
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Java source code (.java files) is typically compiled to bytecode (.class
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files). Bytecode is more compact than Java source code, but it may still
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contain a lot of unused code, especially if it includes program libraries.
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Shrinking programs such as <b>ProGuard</b> can analyze bytecode and remove
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unused classes, fields, and methods. The program remains functionally
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equivalent, including the information given in exception stack traces.
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<h3><a name="obfuscation">What is obfuscation?</a></h3>
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By default, compiled bytecode still contains a lot of debugging information:
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source file names, line numbers, field names, method names, argument names,
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variable names, etc. This information makes it straightforward to decompile
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the bytecode and reverse-engineer entire programs. Sometimes, this is not
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desirable. Obfuscators such as <b>ProGuard</b> can remove the debugging
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information and replace all names by meaningless character sequences, making
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it much harder to reverse-engineer the code. It further compacts the code as a
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bonus. The program remains functionally equivalent, except for the class
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names, method names, and line numbers given in exception stack traces.
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<h3><a name="preverification">What is preverification?</a></h3>
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When loading class files, the class loader performs some sophisticated
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verification of the byte code. This analysis makes sure the code can't
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accidentally or intentionally break out of the sandbox of the virtual machine.
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Java Micro Edition and Java 6 introduced split verification. This means that
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the JME preverifier and the Java 6 compiler add preverification information to
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the class files (StackMap and StackMapTable attributes, respectively), in order
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to simplify the actual verification step for the class loader. Class files can
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then be loaded faster and in a more memory-efficient way. <b>ProGuard</b> can
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perform the preverification step too, for instance allowing to retarget older
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class files at Java 6.
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<h3><a name="optimization">What kind of optimizations does <b>ProGuard</b> support?</a></h3>
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Apart from removing unused classes, fields, and methods in the shrinking step,
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<b>ProGuard</b> can also perform optimizations at the bytecode level, inside
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and across methods. Thanks to techniques like control flow analysis, data flow
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analysis, partial evaluation, static single assignment, global value numbering,
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and liveness analysis, <b>ProGuard</b> can:
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<ul>
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<li>Evaluate constant expressions.</li>
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<li>Remove unnecessary field accesses and method calls.</li>
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<li>Remove unnecessary branches.</li>
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<li>Remove unnecessary comparisons and instanceof tests.</li>
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<li>Remove unused code blocks.</li>
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<li>Merge identical code blocks.</li>
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<li>Reduce variable allocation.</li>
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<li>Remove write-only fields and unused method parameters.</li>
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<li>Inline constant fields, method parameters, and return values.</li>
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<li>Inline methods that are short or only called once.</li>
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<li>Simplify tail recursion calls.</li>
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<li>Merge classes and interfaces.</li>
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<li>Make methods private, static, and final when possible.</li>
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<li>Make classes static and final when possible.</li>
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<li>Replace interfaces that have single implementations.</li>
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<li>Perform over 200 peephole optimizations, like replacing ...*2 by
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...<<1.</li>
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<li>Optionally remove logging code.</li>
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</ul>
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The positive effects of these optimizations will depend on your code and on
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the virtual machine on which the code is executed. Simple virtual machines may
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benefit more than advanced virtual machines with sophisticated JIT compilers.
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At the very least, your bytecode may become a bit smaller.
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<p>
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Some notable optimizations that aren't supported yet:
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<ul>
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<li>Moving constant expressions out of loops.</li>
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<li>Optimizations that require escape analysis
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(<a href="http://www.saikoa.com/dexguard" target="_top">DexGuard</a>
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does).</li>
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</ul>
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<h3><a name="commercial">Can I use <b>ProGuard</b> to process my commercial application?</a></h3>
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Yes, you can. <b>ProGuard</b> itself is distributed under the GPL, but this
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doesn't affect the programs that you process. Your code remains yours, and
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its license can remain the same.
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<h3><a name="jdk1.4">Does <b>ProGuard</b> work with Java 2? Java 5? Java 6? Java 7?</a></h3>
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Yes, <b>ProGuard</b> supports all JDKs from 1.1 up to and including 7.0. Java 2
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introduced some small differences in the class file format. Java 5 added
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attributes for generics and for annotations. Java 6 introduced optional
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preverification attributes. Java 7 made preverification obligatory and
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introduced support for dynamic languages. <b>ProGuard</b> handles all versions
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correctly.
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<h3><a name="jme">Does <b>ProGuard</b> work with Java Micro Edition?</a></h3>
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Yes. <b>ProGuard</b> itself runs in Java Standard Edition, but you can freely
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specify the run-time environment at which your programs are targeted,
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including Java Micro Edition. <b>ProGuard</b> then also performs the required
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preverification, producing more compact results than the traditional external
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preverifier.
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<p>
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<b>ProGuard</b> also comes with an obfuscator plug-in for the JME Wireless
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Toolkit.
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<h3><a name="android">Does <b>ProGuard</b> work for Google Android code?</a></h3>
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Yes. Google's <code>dx</code> compiler converts ordinary jar files into files
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that run on Android devices. By preprocessing the original jar files,
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<b>ProGuard</b> can significantly reduce the file sizes and boost the run-time
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performance of the code. It is distributed as part of the Android SDK.
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<a href="http://www.saikoa.com/dexguard" target="_top"><b>DexGuard</b></a>,
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<b>ProGuard</b>'s closed-source sibling for Android, offers additional
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optimizations and more application protection.
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<h3><a name="blackberry">Does <b>ProGuard</b> work for Blackberry code?</a></h3>
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It should. RIM's proprietary <code>rapc</code> compiler converts ordinary JME
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jar files into cod files that run on Blackberry devices. The compiler performs
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quite a few optimizations, but preprocessing the jar files with
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<b>ProGuard</b> can generally still reduce the final code size by a few
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percent. However, the <code>rapc</code> compiler also seems to contain some
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bugs. It sometimes fails on obfuscated code that is valid and accepted by other
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JME tools and VMs. Your mileage may therefore vary.
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<h3><a name="ant">Does <b>ProGuard</b> have support for Ant?</a></h3>
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Yes. <b>ProGuard</b> provides an Ant task, so that it integrates seamlessly
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into your Ant build process. You can still use configurations in
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<b>ProGuard</b>'s own readable format. Alternatively, if you prefer XML, you
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can specify the equivalent XML configuration.
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<h3><a name="gradle">Does <b>ProGuard</b> have support for Gradle?</a></h3>
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Yes. <b>ProGuard</b> also provides a Gradle task, so that it integrates into
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your Gradle build process. You can specify configurations in
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<b>ProGuard</b>'s own format or embedded in the Groovy configuration.
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<h3><a name="maven">Does <b>ProGuard</b> have support for Maven?</a></h3>
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2013-07-30 00:58:09 +04:00
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<b>ProGuard</b>'s jar files are also distributed as artefacts from
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the <a href="http://search.maven.org/#search|ga|1|g:%22net.sf.proguard%22"
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target="other">Maven Central</a> repository. There are some third-party
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plugins that support <b>ProGuard</b>, such as the
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<a href="http://code.google.com/p/maven-android-plugin/"
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target="other">android-maven-plugin</a> and the
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<a href="http://mavenproguard.sourceforge.net/" target="other">IDFC Maven
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ProGuard Plug-in</a>.
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2013-03-18 15:50:26 +04:00
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<a href="http://www.saikoa.com/dexguard" target="_top"><b>DexGuard</b></a>
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also comes with a Maven plugin.
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2013-03-18 15:50:26 +04:00
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<h3><a name="gui">Does <b>ProGuard</b> come with a GUI?</a></h3>
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Yes. First of all, <b>ProGuard</b> is perfectly usable as a command-line tool
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that can easily be integrated into any automatic build process. For casual
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users, there's also a graphical user interface that simplifies creating,
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loading, editing, executing, and saving ProGuard configurations.
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<h3><a name="forname">Does <b>ProGuard</b> handle <code>Class.forName</code> calls?</a></h3>
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Yes. <b>ProGuard</b> automatically handles constructs like
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<code>Class.forName("SomeClass")</code> and <code>SomeClass.class</code>. The
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referenced classes are preserved in the shrinking phase, and the string
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arguments are properly replaced in the obfuscation phase.
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<p>
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With variable string arguments, it's generally not possible to determine their
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possible values. They might be read from a configuration file, for instance.
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However, <b>ProGuard</b> will note a number of constructs like
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"<code>(SomeClass)Class.forName(variable).newInstance()</code>". These might
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be an indication that the class or interface <code>SomeClass</code> and/or its
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implementations may need to be preserved. The developer can adapt his
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configuration accordingly.
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<h3><a name="resource">Does <b>ProGuard</b> handle resource files?</a></h3>
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Yes. <b>ProGuard</b> copies all non-class resource files, optionally adapting
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their names and their contents to the obfuscation that has been applied.
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<h3><a name="encrypt">Does <b>ProGuard</b> encrypt string constants?</a></h3>
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No. String encryption in program code has to be perfectly reversible by
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definition, so it only improves the obfuscation level. It increases the
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footprint of the code. However, by popular demand, <b>ProGuard</b>'s
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closed-source sibling for Android, <a href="http://www.saikoa.com/dexguard"
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target="_top"><b>DexGuard</b></a>, does provide string encryption, along with
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more protection techniques against static and dynamic analysis.
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<h3><a name="flow">Does <b>ProGuard</b> perform flow obfuscation?</a></h3>
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Not explicitly. Control flow obfuscation injects additional branches into the
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bytecode, in an attempt to fool decompilers. <b>ProGuard</b> does not do this,
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in order to avoid any negative effects on performance and size. However, the
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optimization step often already restructures the code to the point where most
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decompilers get confused.
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<h3><a name="incremental">Does <b>ProGuard</b> support incremental obfuscation?</a></h3>
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Yes. This feature allows you to specify a previous obfuscation mapping file in
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a new obfuscation step, in order to produce add-ons or patches for obfuscated
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code.
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<h3><a name="keywords">Can <b>ProGuard</b> obfuscate using reserved keywords?</a></h3>
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Yes. You can specify your own obfuscation dictionary, such as a list of
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reserved key words, identifiers with foreign characters, random source files,
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or a text by Shakespeare. Note that this hardly improves the obfuscation.
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Decent decompilers can automatically replace reserved keywords, and the effect
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can be undone fairly easily, by obfuscating again with simpler names.
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<h3><a name="stacktrace">Can <b>ProGuard</b> reconstruct obfuscated stack traces?</a></h3>
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Yes. <b>ProGuard</b> comes with a companion tool, <b>ReTrace</b>, that can
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'de-obfuscate' stack traces produced by obfuscated applications. The
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reconstruction is based on the mapping file that <b>ProGuard</b> can write
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out. If line numbers have been obfuscated away, a list of alternative method
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names is presented for each obfuscated method name that has an ambiguous
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reverse mapping. Please refer to the <a href="manual/index.html">ProGuard User
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Manual</a> for more details.
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<address>
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Copyright © 2002-2013
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<a target="other" href="http://www.lafortune.eu/">Eric Lafortune</a>.
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