To compile a Java code into an APK (Android Application Package) file, you need to follow these steps:

1. Set up the Java Development Kit (JDK) on your system. Make sure you have the latest JDK version installed.
  - Download the JDK from the official Oracle website
  - Install the JDK by following the instructions provided by Oracle.

2. Set up the Android Studio Integrated Development Environment (IDE).
  - Download and install Android Studio from the official website
  - Follow the installation wizard.
  - Open Android Studio and set up the necessary SDK platforms and tools.

3. Create a new Android project in Android Studio.
  - Open Android Studio.
  - Click on "Start a new Android Studio project" or navigate to "File -> New -> New Project."
  - Choose an application name, domain, and project location.
  - Select the minimum SDK version and target SDK version.
  - Choose an empty Activity template or customize it based on your requirements.
  - Click on "Finish" to create the project.

4. Copy your Java code into the project directory.
  - Open the project in Android Studio.
  - Navigate to the "app" directory within the project.
  - Replace the default Activity Java file with your own Java file.
  - Ensure your Java file meets the requirements for an Android application.

5. Build the project.
  - Click on "Build -> Build Bundle(s) / APK(s) -> Build APK(s)."
  - Android Studio will compile your Java code along with the necessary resources and dependencies.
  - Once the build process completes, Android Studio will provide you with the APK file path.

6. Locate the generated APK file.
  - After the build process finishes, Android Studio will display a yellow notification with the APK file's location.
  - Click on the "locate" option within the notification to open the folder containing the APK file.
  - The generated APK file will be named "app-debug.apk" or "app-release.apk."

You have successfully compiled your Java code into an APK file using Android Studio.