[Android application] Compare code between Kotlin and Java

class MainActivity : AppCompatActivity() {
    // kotlin code 

 var a: Int = 10 

 var b: Int = 5 

 override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main) 

 var btn_hello = findViewById(R.id.btn_hello) as Button 

 var c = a + b 

 var msg: String = "Kotlin" 

 btn_hello.setOnClickListener { 

 view -> 

 Toast.makeText(applicationContext, msg, Toast.LENGTH_SHORT).show() 

        } 

    }
}