[Android] Install Kotlin language for Android Studio

class MainActivity : AppCompatActivity() {
 private var TAG: String = "MainActivity" 

 private var a: Int = 0 

 private var b: Int = 0
 

 override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState) 

 a = 10 

 b = 25 

 Log.d(TAG, "result:" + (a + b)) 

 // result:35 

  }
}