KotlinProject | repo help for all developer who want to learn android | Android library

I'm a newbie in Kotlin and I'm currently learning how to integrate Gradle with Kotlin. Looking up in the internet I saw this code.

I have a project that uses a Gradle multi-project build. Some of the sub-projects are written in Java, other newer ones in Kotlin.

We have one top-level build.gradle file. This file contains following part:

I'm from Objective-C background. I have to create objects programmatically, so trying to explore it in Java and in Kotlin.

In Objective-C We used to declare the instance variables in .h files and access them anywhere in the .m files, is there something similar interface where we declare the variables and object types somewhere and then access them in our kotlin class?

I'm trying to declare a variable that I can access in different methods inside of a class (e.g MainActivity). In Java, it works fine however in Kotlin, I guess I'm having trouble to declare it without initializing it. Need help.

So, basically I've wondered how would Kotlin's string interpolation look in Java (decompiled bytecode). At first I've thought it would use StringBuffer (or StringBuilder), or String.format(), but it seems that it does concatenation. Is it really optimal to do so and what about the String Pool?

Here is my Kotlin code: