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### About Fernflower
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Fernflower is the first actually working analytical decompiler for Java and
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probably for a high-level programming language in general. Naturally it is still
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under development, please send your bug reports and improvement suggestions at
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fernflower.decompiler@gmail.com
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### Licence
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Fernflower is licenced under the [Apache Licence Version 2.0](http://www.apache.org/licenses/LICENSE-2.0).
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### Running from command line
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`java -jar fernflower.jar [-<option>=<value>]* [<source>]+ <destination>`
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\* means 0 or more times\
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\+ means 1 or more times
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\<source>: file or directory with files to be decompiled. Directories are recursively scanned. Allowed file extensions are class, zip and jar.
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Sources prefixed with -e= mean "library" files that won't be decompiled, but taken into account when analysing relationships between
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classes or methods. Especially renaming of identifiers (s. option 'ren') can benefit from information about external classes.
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\<destination>: destination directory
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\<option>, \<value>: a command-line option with the corresponding value (see "Command-line options" below).
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##### Examples:
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`java -jar fernflower.jar -hes=0 -hdc=0 c:\Temp\binary\ -e=c:\Java\rt.jar c:\Temp\source\`
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`java -jar fernflower.jar -dgs=1 c:\Temp\binary\library.jar c:\Temp\binary\Boot.class c:\Temp\source\`
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### Command-line options
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With the exception of mpm and urc the value of 1 means the option is activated, 0 - deactivated. Default
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value, if any, is given between parentheses.
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Typically, the following options will be changed by user, if any: hes, hdc, dgs, mpm, ren, urc
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The rest of options can be left as they are: they are aimed at professional reverse engineers.
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- rbr (1): hide bridge methods
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- rsy (0): hide synthetic class members
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- din (1): decompile inner classes
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- dc4 (1): collapse 1.4 class references
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- das (1): decompile assertions
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- hes (1): hide empty super invocation
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- hdc (1): hide empty default constructor
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- dgs (0): decompile generic signatures
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- ner (1): assume return not throwing exceptions
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- den (1): decompile enumerations
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- rgn (1): remove getClass() invocation, when it is part of a qualified new statement
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- lit (0): output numeric literals "as-is"
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- asc (0): encode non-ASCII characters in string and character literals as Unicode escapes
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- bto (1): interpret int 1 as boolean true (workaround to a compiler bug)
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- nns (1): allow for not set synthetic attribute (workaround to a compiler bug)
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- uto (1): consider nameless types as java.lang.Object (workaround to a compiler architecture flaw)
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- udv (1): reconstruct variable names from debug information, if present
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- rer (1): remove empty exception ranges
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- fdi (1): de-inline finally structures
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- mpm (0): maximum allowed processing time per decompiled method, in seconds. 0 means no upper limit
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- ren (0): rename ambiguous (resp. obfuscated) classes and class elements
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- urc: full name of user-supplied class implementing IIdentifierRenamer. It is used to determine which class identifiers
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should be renamed and provides new identifier names (see "Renaming identifiers")
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- inn (1): check for IntelliJ IDEA-specific @NotNull annotation and remove inserted code if found
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- lac (0): decompile lambda expressions to anonymous classes
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- nls (0): define new line character to be used for output. 0 - '\r\n' (Windows), 1 - '\n' (Unix), default is OS-dependent
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- ind: indentation string (default is 3 spaces)
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- log (INFO): a logging level, possible values are TRACE, INFO, WARN, ERROR
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### Renaming identifiers
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Some obfuscators give classes and their member elements short, meaningless and above all ambiguous names. Recompiling of such
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code leads to a great number of conflicts. Therefore it is advisable to let the decompiler rename elements in its turn,
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ensuring uniqueness of each identifier.
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Option 'ren' (i.e. -ren=1) activates renaming functionality. Default renaming strategy goes as follows:
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- rename an element if its name is a reserved word or is shorter than 3 characters
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- new names are built according to a simple pattern: (class|method|field)_\<consecutive unique number>
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You can overwrite this rules by providing your own implementation of the 4 key methods invoked by the decompiler while renaming. Simply
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pass a class that implements org.jetbrains.java.decompiler.main.extern.IIdentifierRenamer in the option 'urc'
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(e.g. -urc=com.example.MyRenamer) to Fernflower. The class must be available on the application classpath.
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The meaning of each method should be clear from naming: toBeRenamed determine whether the element will be renamed, while the other three
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provide new names for classes, methods and fields respectively.
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