What is the purpose of kotlin-stdlib-jdk dependency?

Question

When we create a new project in Android Studio following line is added to the app modules gradle file.

implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"

But what is the purpose of adding this dependency?

I thought it allows us to use Kotlin standard library, but it is not about making Kotlin standard library available to us, since we can use Kotlin standard library functions without it.

Answer 1

But what is the purpose of adding this dependency?

It contains the Kotlin standard library.

we can use Kotlin standard library functions without it

You are getting the Kotlin standard library through a transitive dependency.

For example, in Android Studio 3.5.3, I created a new "Empty Activity" project. I then trimmed back the dependencies to:

dependencies {
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.core:core-ktx:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
}

However, in the "External Libraries" portion of the explorer tree, I could still see the Kotlin standard library. Running the dependencies task shows that the Kotlin standard library is pulled in by core-ktx and the kotlin-android-extensions plugin:

releaseRuntimeClasspath - Runtime classpath of compilation 'release' (target  (androidJvm)).
+--- org.jetbrains.kotlin:kotlin-android-extensions-runtime:1.3.61
|    \--- org.jetbrains.kotlin:kotlin-stdlib:1.3.61
|         +--- org.jetbrains.kotlin:kotlin-stdlib-common:1.3.61
|         \--- org.jetbrains:annotations:13.0
+--- androidx.appcompat:appcompat:1.1.0
|    +--- androidx.annotation:annotation:1.1.0
|    +--- androidx.core:core:1.1.0
|    |    +--- androidx.annotation:annotation:1.1.0
|    |    +--- androidx.lifecycle:lifecycle-runtime:2.0.0 -> 2.1.0
|    |    |    +--- androidx.lifecycle:lifecycle-common:2.1.0
|    |    |    |    \--- androidx.annotation:annotation:1.1.0
|    |    |    +--- androidx.arch.core:core-common:2.1.0
|    |    |    |    \--- androidx.annotation:annotation:1.1.0
|    |    |    \--- androidx.annotation:annotation:1.1.0
|    |    +--- androidx.versionedparcelable:versionedparcelable:1.1.0
|    |    |    +--- androidx.annotation:annotation:1.1.0
|    |    |    \--- androidx.collection:collection:1.0.0 -> 1.1.0
|    |    |         \--- androidx.annotation:annotation:1.1.0
|    |    \--- androidx.collection:collection:1.0.0 -> 1.1.0 (*)
|    +--- androidx.cursoradapter:cursoradapter:1.0.0
|    |    \--- androidx.annotation:annotation:1.0.0 -> 1.1.0
|    +--- androidx.fragment:fragment:1.1.0
|    |    +--- androidx.annotation:annotation:1.1.0
|    |    +--- androidx.core:core:1.1.0 (*)
|    |    +--- androidx.collection:collection:1.1.0 (*)
|    |    +--- androidx.viewpager:viewpager:1.0.0
|    |    |    +--- androidx.annotation:annotation:1.0.0 -> 1.1.0
|    |    |    +--- androidx.core:core:1.0.0 -> 1.1.0 (*)
|    |    |    \--- androidx.customview:customview:1.0.0
|    |    |         +--- androidx.annotation:annotation:1.0.0 -> 1.1.0
|    |    |         \--- androidx.core:core:1.0.0 -> 1.1.0 (*)
|    |    +--- androidx.loader:loader:1.0.0
|    |    |    +--- androidx.annotation:annotation:1.0.0 -> 1.1.0
|    |    |    +--- androidx.core:core:1.0.0 -> 1.1.0 (*)
|    |    |    +--- androidx.lifecycle:lifecycle-livedata:2.0.0
|    |    |    |    +--- androidx.arch.core:core-runtime:2.0.0
|    |    |    |    |    +--- androidx.annotation:annotation:1.0.0 -> 1.1.0
|    |    |    |    |    \--- androidx.arch.core:core-common:2.0.0 -> 2.1.0 (*)
|    |    |    |    +--- androidx.lifecycle:lifecycle-livedata-core:2.0.0
|    |    |    |    |    +--- androidx.lifecycle:lifecycle-common:2.0.0 -> 2.1.0 (*)
|    |    |    |    |    +--- androidx.arch.core:core-common:2.0.0 -> 2.1.0 (*)
|    |    |    |    |    \--- androidx.arch.core:core-runtime:2.0.0 (*)
|    |    |    |    \--- androidx.arch.core:core-common:2.0.0 -> 2.1.0 (*)
|    |    |    \--- androidx.lifecycle:lifecycle-viewmodel:2.0.0 -> 2.1.0
|    |    |         \--- androidx.annotation:annotation:1.1.0
|    |    +--- androidx.activity:activity:1.0.0
|    |    |    +--- androidx.annotation:annotation:1.1.0
|    |    |    +--- androidx.core:core:1.1.0 (*)
|    |    |    +--- androidx.lifecycle:lifecycle-runtime:2.1.0 (*)
|    |    |    +--- androidx.lifecycle:lifecycle-viewmodel:2.1.0 (*)
|    |    |    \--- androidx.savedstate:savedstate:1.0.0
|    |    |         +--- androidx.annotation:annotation:1.1.0
|    |    |         +--- androidx.arch.core:core-common:2.0.1 -> 2.1.0 (*)
|    |    |         \--- androidx.lifecycle:lifecycle-common:2.0.0 -> 2.1.0 (*)
|    |    \--- androidx.lifecycle:lifecycle-viewmodel:2.0.0 -> 2.1.0 (*)
|    +--- androidx.appcompat:appcompat-resources:1.1.0
|    |    +--- androidx.annotation:annotation:1.1.0
|    |    +--- androidx.core:core:1.0.1 -> 1.1.0 (*)
|    |    +--- androidx.vectordrawable:vectordrawable:1.1.0
|    |    |    +--- androidx.annotation:annotation:1.1.0
|    |    |    +--- androidx.core:core:1.1.0 (*)
|    |    |    \--- androidx.collection:collection:1.1.0 (*)
|    |    +--- androidx.vectordrawable:vectordrawable-animated:1.1.0
|    |    |    +--- androidx.vectordrawable:vectordrawable:1.1.0 (*)
|    |    |    +--- androidx.interpolator:interpolator:1.0.0
|    |    |    |    \--- androidx.annotation:annotation:1.0.0 -> 1.1.0
|    |    |    \--- androidx.collection:collection:1.1.0 (*)
|    |    \--- androidx.collection:collection:1.0.0 -> 1.1.0 (*)
|    +--- androidx.drawerlayout:drawerlayout:1.0.0
|    |    +--- androidx.annotation:annotation:1.0.0 -> 1.1.0
|    |    +--- androidx.core:core:1.0.0 -> 1.1.0 (*)
|    |    \--- androidx.customview:customview:1.0.0 (*)
|    \--- androidx.collection:collection:1.0.0 -> 1.1.0 (*)
+--- androidx.core:core-ktx:1.0.2
|    +--- org.jetbrains.kotlin:kotlin-stdlib:1.2.50 -> 1.3.61 (*)
|    +--- androidx.annotation:annotation:1.0.2 -> 1.1.0
|    \--- androidx.core:core:1.0.2 -> 1.1.0 (*)
\--- androidx.constraintlayout:constraintlayout:1.1.3
     \--- androidx.constraintlayout:constraintlayout-solver:1.1.3

When I removed those two things, now the Kotlin standard library was no longer pulled in as a transitive dependency... and now I don't have access to Kotlin standard library stuff like listOf().