Gist showing how to enable Java 8 on an Android App

build.gradle

android {
    // ... all the other configurations
    
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    kotlinOptions {
        jvmTarget = "1.8"
    }
}

dependencies {
    // ...
}