MainActivity After Converting

MainActivity.kt

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val toolbar = findViewById(R.id.toolbar) as Toolbar?
        setSupportActionBar(toolbar)

        val fab = findViewById(R.id.fab) as FloatingActionButton?
        fab?.setOnClickListener(View.OnClickListener { view -> Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG).setAction("Action", null).show() })
    }
}