Decompiling an Android APK file

I recently needed to look into another Android app to see how they implemented some strange UI behaviour. There are a few steps neccessary to get the source code of an app.

1. Download the APK from the device.
2. Convert the APK file to a JAR
3. Decompile the JAR

Download the APK from the device

This can be done using the Android SDK platform tools. Go to your SDK directory and find platform-tools/adb.

If you don't know where your application is installed on your device follow these instructions:

Type 

adb shell

This gives you a Linux shell on your device. Now type:

pm list packages -f

This will give you a list of all your installed applications and the paths where they are located in the filesystem.

Exit the shell and download the APK via:

adb pull <Path to the APK file on the device>

Now you can find the APK file in your current directory.

Convert the APK file to a JAR

Now we use the dex2jar tool to convert the Dalvik executable files into class files inside a JAR. Download the tool from the github repository and run

sh d2j-dex2jar.sh -f ~/path/to/apk_to_decompile.apk

This creates the JAR archive in the current directory.

Decompile the JAR

Now we can use the Java Decompiler to view the contents of the JAR archive. Just open the JAR archive in the Decompiler and browse the classes.