Reverse engineering compiled artifacts is an essential practice in debugging, interoperability, and security analysis. Tools such as jadx enable us to convert bytecode into readable Java source code across multiple formats, including Java class files, Android DEX files, JAR archives, and APK packages. This article presents a guide to decompiling these formats using jadx, an open-source decompiler that translates bytecode into readable Java source code.
1. Overview of jadx
jadx is an open source decompiler that provides both command-line and graphical interfaces for converting Android and Java bytecode into human-readable Java source code. It supports a wide range of input formats, including .class, .dex, .jar, and .apk, which makes it a versatile tool for reverse engineering tasks.
In addition to source code reconstruction, jadx can decode Android resources such as XML files and manifest configurations. It also offers features such as syntax highlighting and structured project navigation, enabling efficient analysis of large and complex codebases, particularly in Android applications.
2. Downloading jadx
Installation on macOS
macOS provides a straightforward installation method using Homebrew.
brew install jadx
This command installs jadx and configures it for system-wide usage.
Verify Installation
jadx --version jadx-gui
The commands confirm that jadx is correctly installed and accessible from the terminal. The GUI command launches the graphical interface.
The Homebrew installation automatically manages dependencies and ensures that the executable is available in the system path. This eliminates the need for manual configuration.
Installation on Windows
On Windows systems, jadx is typically installed using the prebuilt archive. The installation process involves downloading the Windows release archive, extracting the ZIP file, and navigating to the bin directory, where users can execute the .bat files directly by double-clicking them.
Building jadx From Source
For advanced users, jadx can be built from source.
git clone https://github.com/skylot/jadx.git cd jadx ./gradlew dist
On Windows:
gradlew.bat dist
After building, the executable scripts are located in:
build/jadx/bin/
Building from source allows customisation and access to the latest development features.
3. Decompiling Java Class Files
Java class files contain bytecode generated by the Java compiler. jadx can convert these files back into readable Java source code.
jadx -d output_class MyClass.class
This command instructs jadx to decompile the specified class file and place the generated source code into the output_dir directory. The -d option defines the destination directory, ensuring that all generated files are organised in a structured manner.
Output Structure:
output_class/
└── sources/
└── com/jcg/example/
└── MyClass.java
The output contains only the reconstructed source code because class files do not include additional resources.
4. Decompiling JAR Files
JAR files are archives that bundle multiple class files and resources. jadx can extract and decompile all contents in a single operation.
jadx app.jar
This configuration allows jadx to unpack the archive, process each class file, and reconstruct the source code. The output directory will contain a folder hierarchy that mirrors the original package structure, which simplifies navigation and analysis.
Output Structure:
output_jar/
├── sources/
│ └── com/example/
│ ├── Main.java
│ └── Utils.java
└── resources/
└── META-INF/
└── MANIFEST.MF
The structure mirrors the original package hierarchy and includes metadata such as the manifest file.
5. Using jadx GUI
APK files are Android application packages that contain DEX files, resources, and metadata. jadx can fully decode APK contents, including layouts and assets. jadx also provides a graphical interface that simplifies navigation and inspection of decompiled code.
jadx-gui app.apk
The graphical interface allows users to browse packages, view decompiled classes, and search within the codebase. It is very useful for large projects where manual navigation through directories would be inefficient. The GUI simplifies analysis of large applications by presenting the project structure in a tree format and enabling quick access to classes and resources.
6. Conclusion
In this article, the process of decompiling .class, JAR and APK files using jadx have been presented. The guide covered installation on macOS and Windows, building from source, and practical command usage to support effective reverse engineering and code analysis.
This article provided an overview of using Java jadx to decompile classes.
