What do you consider bad in code and what would you…

Global variables (val, var at the object level, with many direct accesses).
Using lateinit var without a strong need (prefer nullable val or initialization).
Long, complex functions (more than 10-15 lines of business logic).
Lack or insufficiency of tests (unit tests, instrumental tests).
Code duplication (copy-paste).
Tight coupling of components (Class A directly creates/uses Class B instead of using DI or interfaces).
Insufficient comments for non-obvious parts of the code.
Lack of error handling or using empty catch blocks.
Dependence on specific implementations instead of abstractions (e.g., direct use of Context in ViewModel).
Suboptimal use of collections (e.g., frequent list manipulations instead of sets/maps).
Ignoring linter recommendations (Checkstyle, Detekt).

I would immediately replace:

Using findViewById with View Binding or Data Binding.
Direct use of AsyncTask with Coroutines, RxJava, or WorkManager.
Manual lifecycle management (e.g., adding/removing listeners in onResume/onPause) with Ktx extensions or Lifecycle-aware components.
Old navigation approaches with Navigation Component.
Using Bundle to pass complex objects between activities/fragments with Safe Args, Parcelize, or serialization.

// Example of bad code: Global variable
class BadExampleActivity : AppCompatActivity() {
    var globalCounter = 0 // Bad, hard to track changes

    // ...
}

// Example of better approach: Local scope variable
class GoodExampleActivity : AppCompatActivity() {
    private var localCounter = 0 // Visible only here

    fun incrementCounter() {
        localCounter++
    }
    // ...
}

// Example of bad code: lateinit var without strong need
class AnotherBadExample {
    lateinit var data: String // Can throw UninitializedPropertyAccessException
}

// Example of better approach: Nullable val or initialization
class AnotherGoodExample {
    val data: String? = null // Safe
    // Or:
    val initializedData: String = "Initial Value"
}

// Example of bad code: findViewById
class FindViewByIdActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val textView = findViewById<TextView>(R.id.myTextView) // Boilerplate, nullability issues
        textView.text = "Hello"
    }
}

// Example of better approach: View Binding
class ViewBindingActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        binding.myTextView.text = "Hello" // Safe, type-safe
    }
}

What do you consider bad in code and what would you like to replace immediately?