Add Kotlin to Existing Java Android Project

buildscript {
    ext.kotlin_version = '1.3.31'
    ...
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-android'

...

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