Starting Activity in Kotlin

AccountDetailsActivity.kt

class AccountDetailsActivity : Activity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val accountNumber = intent.getStringExtra(ACCOUNT_NUMBER)
                ?: throw IllegalStateException("ACCOUNT_NUMBER is mandatory in the Intent")
    }

    companion object {
        private val ACCOUNT_NUMBER = "ACCOUNT_NUMBER"

        fun newIntent(context: Context, accountNumber: String): Intent {
            val intent = Intent(context, AccountDetailsActivity::class.java)
            intent.putExtra(ACCOUNT_NUMBER, accountNumber)
            return intent
        }
    }
}

CallingActivity.kt

class CallingActivity : Activity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        
        accountList.clickListener { account ->
            val intent = UserDetailActivity.newIntent(this, account.accountNumber)
            startActivity(intent)
        }
    }
}