In the world of Android development, managing dependencies is an essential aspect of project configuration. Gradle, the powerful build automation tool, offers various configurations to manage these dependencies, among which the most commonly discussed are implementation, api, and compile. While compile has been deprecated in favor of the other two, understanding the distinction between them is crucial for optimal build performance and project stability.

Understanding compile, api, and implementation

Compile: The compile configuration was used in earlier versions of Gradle. It adds the specified library to the classpath and makes it available across all modules of your project. Importantly, it does not distinguish between APIs that your project exposes to other modules and those it consumes itself. This lack of differentiation can lead to inadvertently exposing dependencies to other modules, thereby coupling them too closely together. Due to such issues, compile has been deprecated in Gradle 3.0 and later in favor of api and implementation.

API: The api configuration should be used when you want the library to be exposed to consumers of your library, meaning that any module that depends on your library will have access to the api dependencies as well. This configuration is appropriate when you are developing a library that acts as an intermediary between the dependency and the consumer.

Implementation: The implementation configuration should be used when the dependency is used internally in the module and should not be exposed to other modules. Dependencies declared this way are not leaked into the consumer of the library, leading to a shorter compilation time and reduction in re-compilation when dependencies change.

Example to Demonstrate Difference

To cement these concepts, consider a project structured as follows:

• App Module: Depends on Library Module A
• Library Module A: Uses a logging library

If Library Module A defines its logging library dependency using api, the App Module will also have access to the logging library without explicitly declaring it in its dependencies. However, if Library Module A uses implementation to declare its logging library, then the App Module won't have access to the logging library unless it explicitly declares it too.

1// In Library Module A's build.gradle
2dependencies {
3    api 'com.example.logging:logging-library:1.0.0' // Accessible to App Module
4    // vs
5    implementation 'com.example.logging:logging-library:1.0.0' // Not accessible to App Module
6}

Table: Summary of Differences

Best Practices for Using api and implementation

When to use api:

• Use api when your module exposes part of the dependency as its API. It's common in multi-module projects, where some underlying functionalities are handled by different modules.

When to use implementation:

• Favor implementation for most dependencies to ensure faster compilation time, better encapsulation, and minimized recompilation scope. This is typically the case when creating an application with several modules where most dependencies are internal to each module.

Transitioning from compile to api/implementation: For those migrating from Gradle versions that use compile, it is recommended to evaluate each dependency. If a dependency is only used internally and not meant to be exposed to consumers, switch to implementation. If a dependency forms part of your public API, then api is the appropriate choice.

Conclusion

Optimal use of api and implementation can lead to more maintainable projects with faster build times by ensuring that only the necessary dependencies are recompiled and exposed. By mastering these configurations, developers can effectively manage dependencies in large and complex projects with multiple modules.