I'm trying to figure out what is the difference between api
and implementation
configuration while building my dependencies.
In the documentation, it says that implementation
has better build time, but, seeing this comment in a similar question I got to wonder if is it true.
I'm not an expert in Gradle. I've read the documentation already but I was wondering about an easy-to-understand explanation.
Gradle compile
keyword was deprecated in favor of the api
and implementation
keywords to configure dependencies.
Using api
is the equivalent of using the deprecated compile
, so if you replace all compile
with api
everything will works as always.
To understand the implementation
keyword consider the following example.
EXAMPLE
Suppose you have a library called MyLibrary
that internally uses another library called InternalLibrary
. Something like this:
// 'InternalLibrary' module
public class InternalLibrary {
public static String giveMeAString(){
return "hello";
}
}
// 'MyLibrary' module
public class MyLibrary {
public String myString(){
return InternalLibrary.giveMeAString();
}
}
Suppose the MyLibrary
build.gradle
uses api
configuration in dependencies{}
like this:
dependencies {
api(project(":InternalLibrary"))
}
You want to use MyLibrary
in your code so in your app's build.gradle
you add this dependency:
dependencies {
implementation(project(":MyLibrary"))
}
Using the api
configuration (or deprecated compile
) you can access InternalLibrary
in your application code:
// Access 'MyLibrary' (granted)
MyLibrary myLib = new MyLibrary();
System.out.println(myLib.myString());
// Can ALSO access the internal library too (but you shouldn't)
System.out.println(InternalLibrary.giveMeAString());
In this way the module MyLibrary
is potentially "leaking" the internal implementation of something. You shouldn't (be able to) use that because it's not directly imported by you.
The implementation
configuration was introduced to prevent this.
So now if you use implementation
instead of api
in MyLibrary
:
dependencies {
implementation(project(":InternalLibrary"))
}
you won't be able to call InternalLibrary.giveMeAString()
in your app code anymore.
This sort of boxing strategy allows Android Gradle plugin to know that if you edit something in InternalLibrary
, it must only trigger the recompilation of MyLibrary
and not the recompilation of your entire app, because you don't have access to InternalLibrary
.
When you have a lot of nested dependencies this mechanism can speed up the build a lot. (Watch the video linked at the end for a full understanding of this)
CONCLUSIONS
When you switch to the new Android Gradle plugin 3.X.X, you should replace all your compile
with the implementation
keyword *(1). Then try to compile and test your app. If everything it's ok leave the code as is, if you have problems you probably have something wrong with your dependencies or you used something that now is private and not more accessible. *Suggestion by Android Gradle plugin engineer Jerome Dochez (1))
If you are a library mantainer you should use api
for every dependency which is needed for the public API of your library, while use implementation
for test dependencies or dependencies which must not be used by the final users.
Useful article Showcasing the difference between implementation and api
REFERENCES (This is the same video splitted up for time saving)
Google I/O 2017 - How speed up Gradle builds (FULL VIDEO)
Google I/O 2017 - How speed up Gradle builds (NEW GRADLE PLUGIN 3.0.0 PART ONLY)
Google I/O 2017 - How speed up Gradle builds (reference to 1*)