Android apps contain various class files, each of which contain different methods, properties and fields that handle the application's interactions with users and data. When an app is installed on a device, these class files are combined into a single unit, known as an executable package. This package contains the entire contents of the application, such as resources, code and libraries, which are all compressed into a single .apk file.
Decompiling Android applications is a process of transforming these .apk files from compiled bytecode into human-readable source code. This process can be tricky and requires some degree of familiarity with Android's internal workings. However, tools such as JADX and Dex2Jar make the decompilation process much easier.
In order to decompile an application, the user must first obtain an APK. This can be pulled from an Android device or emulator, or it can be provided directly by the app developer. Then, the APK must be dragged into one of the two decompilation tools mentioned previously in order to obtain the source code.
Once the sourcecode is obtained, it can be manipulated and changed as required. This is especially useful when analysing an application's functionality, as decompiling allows the user to see exactly how the application is working under the hood. Additionally, it is possible to reverse engineer the code to make custom modifications, or to study the way in which an app is written.
For example, let's say the user was interested in creating a custom animation for an application UI. By decompiling the application, the user can view the relevant class file and understand exactly how the animation is coded. The user can then change this code to suit their own needs and create a new, custom animation.
In conclusion, decompiling an Android application is an incredibly useful tool for developers and analysts alike. It provides access to the inner workings of an application and allows users to quickly and easily modify and understand code. By using tools such as JADX and Dex2Jar, users can quickly and easily decompile their desired applications and gain a better understanding of how the application functions.