Android DX vs D8: A Detailed Comparison of Java Compilers in Android Development

In the world of Android development, efficient code compilation is crucial for app performance, speed, and size. Two prominent tools in this context are DX and D8, both used in the compilation process of Android applications. Understanding the differences between DX and D8 can help developers optimize their builds and make better choices when it comes to compiling their Android projects.

This article will provide an in-depth look at both compilers, comparing their features, advantages, and the role they play in Android development. Let’s dive in!

What Is DX?

DX (Dalvik Executable) is a tool introduced in the early versions of Android to convert Java bytecode into Dalvik bytecode (which is used by the Dalvik Virtual Machine, or DVM). The DX compiler was a part of the Android build toolchain that took Java class files and converted them into DEX (Dalvik Executable) files, the format that Android devices understood.

When Android apps were built, Java code was compiled into class files (standard Java bytecode). The DX tool would then take these class files and package them into a DEX file, which would run on Android’s Dalvik Virtual Machine or, later, on the Android Runtime (ART).

Key features of DX:

  1. Dalvik Executable: DX converted Java bytecode into Dalvik bytecode, which was the format Android used for running apps prior to ART.
  2. Optimized for Dalvik: DX was optimized for the Dalvik Virtual Machine, ensuring that applications performed well on devices running older versions of Android.
  3. Part of the Build Process: The DX compiler was an essential part of the Android build process, converting .class files into .dex files before packaging the APK.

However, as Android development evolved, Google introduced the Android Runtime (ART) as a replacement for Dalvik. ART offered improvements in performance, garbage collection, and multi-threading over Dalvik. This shift required a new approach to compilation.

What Is D8?

D8 is the next-generation Java bytecode to DEX compiler introduced as part of Android Studio's build tools. It was developed to replace DX due to its enhanced speed, efficiency, and better handling of modern Java language features. D8 is designed to convert Java bytecode (in .class files) into DEX bytecode (.dex files) for Android applications.

D8 improves upon DX in several ways, making it a more efficient and future-proof tool for Android development.

Key features of D8:

  1. Speed and Efficiency: D8 is much faster than DX. It’s designed to compile Java bytecode into DEX files more efficiently, reducing build times and improving overall performance.
  2. Better Optimization: D8 supports better optimizations of the bytecode, leading to smaller and more efficient DEX files. This can contribute to a reduction in APK size and improved performance on Android devices.
  3. Support for Java 8+: D8 supports modern Java features, including Java 8+ features like lambdas, method references, and default methods. This allows developers to use the latest Java language features without worrying about compatibility issues.
  4. Integration with Android Gradle Plugin: D8 is tightly integrated with the Android Gradle Plugin, ensuring seamless integration with modern Android build systems.
  5. Improved Debugging and Error Handling: D8 provides more informative and helpful error messages during compilation, making debugging easier for developers.

With the introduction of D8, Google effectively phased out DX in favor of D8’s improved performance and modern features.

DX vs D8: Key Differences

Now that we know what DX and D8 are, let’s compare them directly across various categories:

Feature DX D8
Introduction Released in early Android versions Introduced as a replacement for DX in Android Studio 3.0 (2017)
Compilation Speed Slower, especially for large projects Faster and more efficient compilation
Optimizations Limited optimizations compared to D8 Improved optimizations, resulting in smaller and faster APKs
Java Language Support Supports Java 6 and below Supports Java 8+ features (lambdas, method references)
Compatibility Primarily designed for the Dalvik Virtual Machine (DVM) Designed for Android Runtime (ART) and modern Android devices
Error Handling Limited error messages Improved error messages and debugging support
APK Size Larger APK sizes due to less efficient DEX generation Smaller APK sizes due to better DEX optimization
Integration Integrated into older versions of Android Studio Fully integrated into modern Android Studio with Gradle support
Support for Multidex Supports multidex but can be inefficient More efficient handling of multidex
Deprecation Deprecated and replaced by D8 in modern Android development Current standard for compiling Java bytecode into DEX files

Why Was D8 Introduced?

The introduction of D8 was driven by several factors aimed at improving Android development:

  1. Improved Performance: D8 was designed to be faster than DX, particularly for larger codebases. It also leverages modern compiler techniques to provide better performance.
  2. Smaller APK Sizes: D8 optimizes bytecode to produce smaller DEX files, which helps reduce the overall size of APKs, resulting in faster downloads and installations for users.
  3. Support for Modern Java Features: As Java evolved, developers needed support for newer language features like lambdas and method references, which D8 added support for.
  4. Modern Build Tools: The introduction of D8 aligned with the broader changes in Android development, such as the adoption of Android Studio and the Android Gradle Plugin, ensuring that developers could rely on a modern and efficient toolchain.

When Do You Use DX vs D8?

In most modern Android development workflows, D8 is the preferred choice. Since Android Studio 3.0 and higher, D8 has been the default compiler for converting Java bytecode into DEX files. The DX compiler is considered deprecated, and developers are encouraged to use D8 for all new projects.

That said, if you are working with older versions of Android Studio or maintaining legacy projects, you may still encounter DX in some build configurations. However, since D8 has become the standard and provides more optimizations and better performance, it’s advisable to update your tools and dependencies to use D8.

How to Use D8 in Android Studio

In modern versions of Android Studio, D8 is enabled by default. However, if you are manually configuring the build process or want to ensure that D8 is used, you can adjust the build.gradle file for your project.

To enable D8, you need to make sure that the following configuration is in your gradle.properties file:

android.enableD8=true

Additionally, ensure that you are using the latest version of Android Gradle Plugin and Android Studio, as these include the latest updates for D8 and related features.

Conclusion

To sum up, D8 is the modern successor to DX, offering better speed, optimization, support for newer Java features, and more efficient DEX file generation. As of Android Studio 3.0 and beyond, D8 is the default compiler used in the Android build process, replacing the older and slower DX tool.

For developers, D8 brings a host of advantages, from improved performance and smaller APK sizes to better support for Java 8+ features. While DX still plays a role in some legacy projects, it’s clear that D8 is the way forward for modern Android development. If you haven’t already, it’s highly recommended to update your build system to use D8 and take advantage of these improvements.

In short, D8 is the tool that every Android developer should be using today to build efficient, fast, and modern Android applications.