val url = URL("https://example.com")
val connection = url.openConnection() as HttpURLConnection // ❌ Ошибка!

CoroutineScope(Dispatchers.IO).launch {
    val url = URL("https://example.com")
    val connection = url.openConnection() as HttpURLConnection // ✅ Работает!
}

CoroutineScope(Dispatchers.IO).launch {
    val data = fetchData() // Работает в `Worker Thread`
    
    withContext(Dispatchers.Main) {
        textView.text = data // Назад в `UI Thread`
    }
}

val handler = Handler(Looper.getMainLooper())

Thread {
    val data = fetchData() // Работает в `Worker Thread`

    handler.post {
        textView.text = data // Назад в `UI Thread`
    }
}.start()

class MyTask : AsyncTask<Void, Void, String>() {
    override fun doInBackground(vararg params: Void?): String {
        return fetchData() // `Worker Thread`
    }

    override fun onPostExecute(result: String) {
        textView.text = result // `UI Thread`
    }
}

class ChatAdapter : ListAdapter<Message, ChatViewHolder>(DIFF_CALLBACK) {
    
    companion object {
        private val DIFF_CALLBACK = object : DiffUtil.ItemCallback<Message>() {
            override fun areItemsTheSame(oldItem: Message, newItem: Message): Boolean =
                oldItem.id == newItem.id

            override fun areContentsTheSame(oldItem: Message, newItem: Message): Boolean =
                oldItem == newItem // data class сравнит автоматически
        }
    }
}

override fun getChangePayload(oldItem: Message, newItem: Message): Any? {
    return if (oldItem.status != newItem.status) "STATUS_CHANGED" else null
}

override fun onBindViewHolder(holder: ChatViewHolder, position: Int, payloads: MutableList<Any>) {
    if (payloads.contains("STATUS_CHANGED")) {
        holder.updateStatus() // Обновляем только статус
    } else {
        super.onBindViewHolder(holder, position, payloads)
    }
}

fun loadMessages(): Flow<List<Message>> = messageDao.getMessages()

val pager = Pager(
    config = PagingConfig(pageSize = 20),
    pagingSourceFactory = { messageDao.getPagedMessages() }
).flow.cachedIn(viewModelScope)

Glide.with(context)
    .load(user.avatarUrl)
    .circleCrop()
    .placeholder(R.drawable.placeholder)
    .into(imageView)

@Dao
interface MessageDao {
    @Query("SELECT * FROM messages ORDER BY timestamp DESC")
    fun getMessages(): Flow<List<Message>>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertMessages(messages: List<Message>)
}

recyclerView.setHasFixedSize(true)

recyclerView.setItemViewCacheSize(20)

(recyclerView.itemAnimator as SimpleItemAnimator).supportsChangeAnimations = false

fun <T> printType(value: T) {
    println(T::class.simpleName) // ❌ Ошибка! Нельзя использовать `T::class`
}

inline fun <reified T> printType(value: T) {
    println(T::class.simpleName) // ✅ Работает!
}

fun main() {
    printType(123)       // Int
    printType("Hello")   // String
    printType(3.14)      // Double
}

class MyGenericClass<T>(private val type: KClass<T>) {
    fun printType() {
        println(type.simpleName) // ✅ Работает
    }
}

fun main() {
    val obj = MyGenericClass(String::class)
    obj.printType() // String
}

import kotlin.reflect.typeOf

inline fun <reified T> printGenericType() {
    val type = typeOf<T>()
    println(type) // ✅ List<Int>, Map<String, Boolean> и т. д.
}

fun main() {
    printGenericType<List<Int>>() // kotlin.collections.List<kotlin.Int>
}

val apiUrl = "https://api.example.com" // ❌ Если URL изменится, надо менять код

val apiUrl = Config.get("api_url") // ✅ Загружается из настроек

val sharedPrefs = context.getSharedPreferences("settings", Context.MODE_PRIVATE)
val theme = sharedPrefs.getString("app_theme", "light") // ✅ Загружаем тему из настроек

val minVersion = Firebase.remoteConfig.getInt("min_supported_version")

fun getConfigValue(context: Context, key: String): String {
    val json = context.assets.open("config.json").bufferedReader().use { it.readText() }
    val jsonObject = JSONObject(json)
    return jsonObject.getString(key) // ✅ Получаем значение из JSON
}

class MyActivity : AppCompatActivity(), LifecycleOwner {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

class MyObserver : LifecycleObserver {
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onStart() {
        // Код, который выполняется при старте жизненного цикла
        Log.d("MyObserver", "onStart called")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onStop() {
        // Код, который выполняется при остановке жизненного цикла
        Log.d("MyObserver", "onStop called")
    }
}

class MyActivity : AppCompatActivity() {
    private lateinit var myObserver: MyObserver

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

        myObserver = MyObserver()
        lifecycle.addObserver(myObserver)
    }
}

dependencies {
    implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"
}

class MyObserver : LifecycleObserver {
    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    fun onResume() {
        Log.d("MyObserver", "Activity resumed")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    fun onPause() {
        Log.d("MyObserver", "Activity paused")
    }
}

class MyActivity : AppCompatActivity() {
    private lateinit var myObserver: MyObserver

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

        myObserver = MyObserver()
        lifecycle.addObserver(myObserver)
    }
}

<resources>
    <declare-styleable name="CustomButton">
        <attr name="customText" format="string"/>
        <attr name="customTextSize" format="dimension"/>
        <attr name="customTextColor" format="color"/>
    </declare-styleable>
</resources>

class CustomButton @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : AppCompatButton(context, attrs, defStyleAttr) {

    init {
        context.theme.obtainStyledAttributes(attrs, R.styleable.CustomButton, 0, 0).apply {
            try {
                val text = getString(R.styleable.CustomButton_customText) ?: "Default"
                val textSize = getDimension(R.styleable.CustomButton_customTextSize, 16f)
                val textColor = getColor(R.styleable.CustomButton_customTextColor, Color.BLACK)

                setText(text)
                setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize)
                setTextColor(textColor)
            } finally {
                recycle() // Освобождаем ресурсы
            }
        }
    }
}

<com.example.customviews.CustomButton
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:customText="Нажми меня"
    app:customTextSize="20sp"
    app:customTextColor="@android:color/holo_red_dark"/>

val button = findViewById<CustomButton>(R.id.customButton)
button.text = "Новый текст"
button.setTextSize(TypedValue.COMPLEX_UNIT_SP, 24f)
button.setTextColor(Color.BLUE)

class Parent {
    static { System.out.println("1️⃣ Статический блок Parent"); }
    { System.out.println("3️⃣ Обычный блок Parent"); }
    
    Parent() {
        System.out.println("4️⃣ Конструктор Parent");
    }
}

class Child extends Parent {
    static { System.out.println("2️⃣ Статический блок Child"); }
    { System.out.println("5️⃣ Обычный блок Child"); }
    
    Child() {
        System.out.println("6️⃣ Конструктор Child");
    }
}

public class Main {
    public static void main(String[] args) {
        System.out.println("🔹 Создаём объект Child");
        new Child();
    }
}

Статический блок Parent
Статический блок Child
Создаём объект Child
Обычный блок Parent
Конструктор Parent
Обычный блок Child
Конструктор Child

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.widget.Toast;

public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "Сообщение получено!", Toast.LENGTH_SHORT).show();
    }
}

<manifest xmlns:android="https://schemas.android.com/apk/res/android"
    package="com.example.myapp">

    <application
        android:allowBackup="true"
        android:label="@string/app_name"
        android:icon="@mipmap/ic_launcher"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <receiver android:name=".MyBroadcastReceiver">
            <intent-filter>
                <action android:name="android.provider.Telephony.SMS_RECEIVED" />
            </intent-filter>
        </receiver>

    </application>

</manifest>

import android.content.IntentFilter;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private MyBroadcastReceiver myBroadcastReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        myBroadcastReceiver = new MyBroadcastReceiver();
    }

    @Override
    protected void onStart() {
        super.onStart();
        IntentFilter filter = new IntentFilter("android.provider.Telephony.SMS_RECEIVED");
        registerReceiver(myBroadcastReceiver, filter);
    }

    @Override
    protected void onStop() {
        super.onStop();
        unregisterReceiver(myBroadcastReceiver);
    }
}

data class User(val id: Int, val name: String)

fun main() {
    val user1 = User(1, "Alice")
    val user2 = user1.copy(name = "Bob") // Создаём копию с новым именем

    println(user1) // User(id=1, name=Alice)
    println(user2) // User(id=1, name=Bob)
}

sealed class NetworkState {
    object Loading : NetworkState()
    data class Success(val data: String) : NetworkState()
    data class Error(val message: String) : NetworkState()
}

fun handleState(state: NetworkState) {
    when (state) {
        is NetworkState.Loading -> println("Загрузка...")
        is NetworkState.Success -> println("Данные: ${state.data}")
        is NetworkState.Error -> println("Ошибка: ${state.message}")
    }
}

sealed class Result {
    object Loading : Result()
    data class Success(val data: String) : Result()
    data class Error(val message: String) : Result()
}