Explain android runtime for android in detail

The Android Runtime (ART) is the managed runtime environment employed by the Android operating system for executing and managing application code. ART replaced the Dalvik runtime as the default runtime starting with Android 5.0 (Lollipop). The transition from Dalvik to ART brought about significant improvements in performance, efficiency, and overall system responsiveness. Let’s explore the key features and components of the Android Runtime in detail:

1. Compilation Model:

• Dalvik (Deprecated): Dalvik used just-in-time (JIT) compilation. In this model, the bytecode of an Android application is translated into native machine code at runtime, just before the application is executed. This approach allowed for platform independence but incurred a performance overhead during the initial execution.
• ART (Android Runtime): ART introduced ahead-of-time (AOT) compilation. Unlike Dalvik, ART compiles the bytecode into native machine code during the app installation process. This reduces runtime overhead and results in improved application performance, as the compiled code is ready to execute when the app is launched.

2. AOT Compilation:

• With AOT compilation, ART converts the entire application’s bytecode into native machine code before the app is run. This process occurs during the app installation, which means that the compiled code is stored on the device. This approach eliminates the need for on-the-fly bytecode translation during runtime, leading to faster app startup times.

3. Improved Performance:

• AOT compilation contributes to improved application performance. The native machine code generated by ART is optimized for the specific hardware architecture of the device, resulting in more efficient execution compared to the interpretation or JIT compilation used by Dalvik.

4. Reduced Memory Usage:

• ART includes various memory optimizations. For instance, it introduces a more efficient garbage collection algorithm known as the Concurrent Copying Collector, which reduces the impact on application responsiveness. Additionally, ART’s use of ahead-of-time compilation results in the generation of more compact compiled code, reducing the overall memory footprint of applications.

5. Profile-Guided Compilation:

• ART supports profile-guided compilation, which means that the runtime can gather information about the application’s execution patterns. This information is then used to further optimize the compiled code. Profile-guided compilation helps tailor the native code to the specific usage patterns of the application, enhancing overall performance.

6. Garbage Collection:

• ART includes an improved garbage collection mechanism compared to Dalvik. The Concurrent Copying Collector reduces pause times during garbage collection, minimizing disruptions to the application’s execution. This is particularly important for delivering a smoother user experience.

7. Compatibility and Runtime Checks:

• ART maintains compatibility with Dalvik bytecode, allowing existing Android apps developed for Dalvik to run on devices with ART. During installation, ART performs additional runtime checks to ensure that the application’s bytecode is compatible and can be successfully compiled to native code.

8. Dex2Oat Tool:

• The Dex2Oat tool is responsible for converting Dalvik Executable (DEX) files, which contain compiled Android application code, into the optimized native code used by ART. Dex2Oat performs the ahead-of-time compilation during the installation process.

9. 64-Bit Support:

• ART supports both 32-bit and 64-bit architectures. This is essential for devices with 64-bit processors, allowing them to take full advantage of the increased addressable memory and computational capabilities.

10. Compatibility with Java Language:

• Android applications are primarily developed using the Java programming language. ART provides compatibility with Java and supports the Java Native Interface (JNI) for integrating native code written in languages like C or C++.

11. Dynamic Code Loading:

• ART supports dynamic code loading, allowing apps to load code at runtime. This capability is useful for scenarios where specific features or functionalities need to be loaded on-demand.

The adoption of ART as the default runtime in Android has contributed to enhanced app performance, reduced memory usage, and improved overall system responsiveness. By utilizing ahead-of-time compilation and implementing various optimizations, ART plays a crucial role in delivering a smoother and more efficient user experience on Android devices.