Is it possible to decompile java

Is it possible to decompile Java bytecode back to original generic type parameters Ask Question. Asked 4 years, 2 months ago. Active 4 years, 2 months ago.

Viewed 4k times. Improve this question. KOO 5, 2 2 gold badges 23 23 silver badges 51 51 bronze badges. Since types are erased, how do you suppose bytecode to be decompilable to generics?

AndyTurner The question is about restoring original type parameters. Are you talking about restoring type variables in a type definition , or type arguments where a generic type has been instantiated? For example, are you asking whether you could decompile ArrayList. These are two very different possibilities. I am referring to the first scenario. Add a comment. Active Oldest Votes. Type variables and constraints The most basic thing a compiler needs to know in order to consume a generic type is the list of type variables.

Generic supertype signatures Sometimes you write a class that extends a generic class or implements a generic interface. Member signatures The compiler can't verify that you're using a generic type correctly if it doesn't know the full generic types of fields, method parameters and return types.

Local variables It's not necessary to preserve information about local variable types in order to consume a type. You can force javac to emit them by passing -g:vars , but I believe they're omitted by default Call sites One of the biggest issues for decompilers, mostly affecting generic inference within method bodies, is that call sites invoking generic methods retain no information about type arguments.

How this affects decompilation Modern Java decompilers like Procyon and CFR should be able to reconstruct generic types reasonably well. At the API level, though—type and member signatures—the results should be spot-on. Caveats Strictly speaking, all of the metadata described here is optional : it's only needed at compile time or decompile time.

Improve this answer. Mike Strobel Mike Strobel My pleasure. Try using javap -v on a generic type sometime and look for Signature attributes to see what gets written out. You can also use Procyon with -r -v to force verbose disassembly mode bytecode output.

Just run javap with -c option and it will print bytecodes of class file as shown in below example:. JD-Eclipse is easy to use the eclipse plugin and has detailed installation steps documented. Apart from these are much more which I haven't tried. Just go to the Eclipse marketplace and you will see a lot of those.

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How to design a vending machine in Java? How HashMap works in Java? Secondly, though I usually balk at, "Look at my library that does this! Strobel's readme that he links to, above, is worth a close read. It would have been a great answer itself, but is admittedly probably a bit too long for SE. Keep it up! Signus Thanks, I'm glad my work proved useful to you :. Modern Tools JD-Gui Probably one of the most widely used tools for Java decompilation, as it is easy to use and provides a graphical user interface which allows to quickly open up and inspect a class file or JAR.

CFR Free, and open source. Also a command line tool. This one does an even better job and is slightly faster. Procyon Open source , and also aims to deal with Java 8 features lambdas, :: operator. Does not yet support Java 8 features. Recaf A Java Bytecode editor and reverse engineering tool aimed at being intuitive to use.

It supports jars, wars, classes, and extracting classes from running Java processes. It uses FernFlower, Procyon and CFR for decompilation, makes this an awesome visual tool using state-of-art decompilers: Enigma A tool specifically geared for deobfuscation : Originally used to deobfuscate Minecraft versions.

Uses Procyon internally. This answer may need to be updated. It appears that JD-Gui is being actively developed as of March I have some java 7 code that I'm attempting to write some aspects for.

The built-in intellij decompiler in some cases has incorrect variable names and can leave out blocks of code. JD-Gui shows those blocks and also displays what appears to be more accurate variable names. It also shows side-by-side the differences between an old version and new version of JD-Gui. It's worth looking at if you're doing some serious reversing. From the readme: "The Krakatau decompiler takes a different approach to most Java decompilers. It can be thought of more as a compiler whose input language is Java bytecode and whose target language happens to be Java source code.

Krakatau takes in arbitrary bytecode, and attempts to transform it to equivalent Java code. This makes it robust to minor obfuscation, though it has the drawback of not reconstructing the "original" source, leading to less readable output than a pattern matching decompiler would produce for unobfuscated Java classes.

That is actually the output of the disassembler. The decompiler decompiles to Java output. I'm the developer — Antimony. The virtual machine is a program that converts the platform-generalized bytecode into the native code that will run in a specific processor.

How do I decompile a game? How does a Java decompiler work? Java Decompiler. A Java decompiler is a special type of decompiler which takes a class file as input and produces Java source code as output.

This process becomes very useful for competitors to dig into the source code and understand the working of a Java program made by someone else. Can I get source code from APK file? In Android studio 2. You will see it's source code.

Can APK be decompiled? Decompilation of APK file is possible. But it might be difficult to understand the code if it is obfuscated.