class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
    
    override fun onDestroy() {
        super.onDestroy()
        // Cleanup
    }
}

class UserFragment : Fragment() {
    private val viewModel: UserViewModel by viewModels()
    
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        viewModel.user.observe(viewLifecycleOwner) { user ->
            updateUI(user)
        }
    }
}

// Explicit
startActivity(Intent(this, DetailActivity::class.java))

// Implicit
startActivity(Intent(Intent.ACTION_VIEW, Uri.parse("https://example.com")))