// 示例：典型的Android Activity中Java代碼
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); // 綁定佈局
    }
}

public class User {
    // 成員變量
    private String name;
    private int age;

    // 構造函數
    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // 方法
    public void introduce() {
        System.out.println("Hello, I'm " + name + ", " + age + " years old.");
    }
}

User user = new User("Alice", 25);
user.introduce(); // 輸出: Hello, I'm Alice, 25 years old.

classDiagram
    class User {
        -String name
        -int age
        +User(String name, int age)
        +void introduce()
    }
    note right of User
      表示User類的UML圖
      展示封裝與行為
    end note

User user1 = new User("Bob", 30);
User user2 = new User("Charlie", 35);
user1.introduce(); // Bob的信息
user2.introduce(); // Charlie的信息

user.age = -5; // 非法年齡，但編譯通過！

public class User {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        if (age < 0 || age > 150) {
            throw new IllegalArgumentException("Invalid age: " + age);
        }
        this.age = age;
    }
}

user.setAge(-5); // 拋出IllegalArgumentException

public class User {
    private String name;
    private int age;
    private String email;

    // 無參構造函數
    public User() {
        this.name = "Unknown";
        this.age = 0;
        this.email = "unknown@example.com";
    }

    // 單參構造函數
    public User(String name) {
        this.name = name;
        this.age = 18; // 默認成年
        this.email = "no-email";
    }

    // 全參構造函數
    public User(String name, int age, String email) {
        this.name = name;
        this.age = age;
        this.email = email;
    }

    // 利用this()調用其他構造函數
    public User(String name, int age) {
        this(name, age, name.toLowerCase() + "@example.com"); // 自動生成郵箱
    }
}

User u1 = new User();                    // 使用默認值
User u2 = new User("David");             // 指定名字，其餘默認
User u3 = new User("Eve", 28);           // 自動生成郵箱
User u4 = new User("Frank", 32, "f@x.com");// 完全自定義

// 父類
public class Person {
    protected String name;
    protected int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void walk() {
        System.out.println(name + " is walking.");
    }

    public void eat() {
        System.out.println(name + " is eating.");
    }
}

// 子類
public class Student extends Person {
    private String studentId;
    private String major;

    public Student(String name, int age, String studentId, String major) {
        super(name, age); // 調用父類構造函數
        this.studentId = studentId;
        this.major = major;
    }

    public void study() {
        System.out.println(name + " is studying " + major);
    }
}

Student s = new Student("Grace", 20, "S001", "Computer Science");
s.walk();   // 繼承自Person
s.eat();    // 繼承自Person
s.study();  // Student特有方法

Grace is walking.
Grace is eating.
Grace is studying Computer Science

graph TD
    A[Object] --> B[Context]
    B --> C[ContextWrapper]
    C --> D[ContextThemeWrapper]
    D --> E[Activity]
    E --> F[AppCompatActivity]

@Override
public void eat() {
    System.out.println(name + " is eating healthy food.");
}

@Override
public void walk() {
    super.walk(); // 先執行父類邏輯
    System.out.println("Walking with a backpack."); // 新增行為
}

Person p1 = new Student("Hannah", 19, "S002", "Mathematics");
p1.eat(); // 輸出: Hannah is eating healthy food.

List<Person> people = new ArrayList<>();
people.add(new Person("John", 40));
people.add(new Student("Ivy", 21, "S003", "Physics"));

for (Person person : people) {
    person.eat(); // 根據實際類型動態調用
}

public abstract class Animal {
    protected String name;

    public Animal(String name) {
        this.name = name;
    }

    // 抽象方法，強制子類實現
    public abstract void makeSound();

    // 具體方法，提供通用行為
    public void sleep() {
        System.out.println(name + " is sleeping.");
    }
}

public class Dog extends Animal {
    public Dog(String name) {
        super(name);
    }

    @Override
    public void makeSound() {
        System.out.println(name + " barks: Woof!");
    }
}

public interface Flyable {
    void fly(); // 抽象方法

    default void land() {
        System.out.println("Landing safely.");
    }

    static void describe() {
        System.out.println("Can fly in the sky.");
    }
}

public class Bird implements Flyable {
    private String name;

    public Bird(String name) {
        this.name = name;
    }

    @Override
    public void fly() {
        System.out.println(name + " is flying.");
    }
}

classDiagram
    Animal <|-- Dog
    Animal <|-- Cat
    Flyable <|.. Bird
    Flyable <|.. Airplane
    note right of Flyable
      接口表示“能飛”的能力
      可被動物或機器實現
    end note

button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(ctx, "Clicked!", Toast.LENGTH_SHORT).show();
    }
});

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    Log.e("TAG", "Divide by zero", e);
} finally {
    cleanup();
}

public class NetworkException extends Exception {
    public NetworkException(String msg) {
        super(msg);
    }
}

stateDiagram-v2
    [*] --> Created
    Created --> Started: onCreate()
    Started --> Resumed: onStart()
    Resumed --> Paused: onResume()
    Paused --> Stopped: onPause()
    Stopped --> Destroyed: onStop()
    Destroyed --> [*]: onDestroy()

    Resumed --> Paused: 用户離開當前界面
    Paused --> Resumed: 用户返回
    Paused --> Stopped: 完全不可見
    Stopped --> Started: 再次可見

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate called");
        // 初始化UI控件
        TextView tv = findViewById(R.id.textView);
        tv.setText("Hello Lifecycle!");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.d(TAG, "onStart called");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume called");
        // 恢復攝像頭預覽或GPS定位
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause called");
        // 停止錄音或暫停遊戲
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.d(TAG, "onStop called");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy called");
    }
}

<activity
    android:name=".MainActivity"
    android:screenOrientation="portrait"
    android:configChanges="keyboardHidden|orientation|screenSize" />

@Override
public void onConfigurationChanged(@NonNull Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {
        Toast.makeText(this, "切換至橫屏", Toast.LENGTH_SHORT).show();
    }
}

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    EditText input = findViewById(R.id.editText);
    String text = input.getText().toString();
    outState.putString("user_input", text); // 保存輸入內容
    Log.d(TAG, "State saved: " + text);
}

@Override
protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    String restoredText = savedInstanceState.getString("user_input");
    EditText input = findViewById(R.id.editText);
    input.setText(restoredText);
    Log.d(TAG, "State restored: " + restoredText);
}

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    outState.putInt("score", currentScore);
    outState.putBoolean("isGameRunning", isGameActive);
    outState.putParcelable("player", currentPlayer); // 實現 Parcelable 接口
    super.onSaveInstanceState(outState);
}

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

    if (savedInstanceState != null) {
        currentScore = savedInstanceState.getInt("score");
        isGameActive = savedInstanceState.getBoolean("isGameRunning");
        currentPlayer = savedInstanceState.getParcelable("player");
    } else {
        // 初始值設置
        currentScore = 0;
        isGameActive = true;
    }
}

public class Player implements Parcelable {
    private String name;
    private int level;

    public Player(String name, int level) {
        this.name = name;
        this.level = level;
    }

    protected Player(Parcel in) {
        name = in.readString();
        level = in.readInt();
    }

    public static final Creator<Player> CREATOR = new Creator<Player>() {
        @Override
        public Player createFromParcel(Parcel in) {
            return new Player(in);
        }

        @Override
        public Player[] newArray(int size) {
            return new Player[size];
        }
    };

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(name);
        dest.writeInt(level);
    }
}

Intent intent = new Intent(this, DetailActivity.class);
intent.putExtra("user_id", 12345);
startActivity(intent);

Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setData(Uri.parse("https://www.example.com"));
if (intent.resolveActivity(getPackageManager()) != null) {
    startActivity(intent);
}

<activity android:name=".ShareActivity">
    <intent-filter>
        <action android:name="android.intent.action.SEND" />
        <category android:name="android.intent.category.DEFAULT" />
        <data android:mimeType="text/plain" />
    </intent-filter>
</activity>

Intent intent = new Intent(Intent.ACTION_SEND);
intent.setType("text/plain");
intent.putExtra(Intent.EXTRA_TEXT, "分享內容");
startActivity(Intent.createChooser(intent, "請選擇分享方式"));

<intent-filter>
    <action android:name="android.intent.action.VIEW"/>
    <category android:name="android.intent.category.DEFAULT"/>
    <data android:scheme="http" android:host="example.com"/>
</intent-filter>

Bundle bundle = new Bundle();
bundle.putString("name", "Alice");
bundle.putInt("age", 28);
bundle.putParcelable("profile", profile);

Intent intent = new Intent(this, ProfileActivity.class);
intent.putExtras(bundle);
startActivity(intent);

<!-- 示例：使用ConstraintLayout實現居中帶偏移的按鈕 -->
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/btn_center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="居中按鈕"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintVertical_bias="0.3" />

</androidx.constraintlayout.widget.ConstraintLayout>

graph TD
    A[開始選擇佈局] --> B{是否需要線性排列?}
    B -- 是 --> C[使用LinearLayout]
    B -- 否 --> D{是否有多個相對定位需求?}
    D -- 是 --> E[避免深層嵌套 → 使用ConstraintLayout]
    D -- 否 --> F{是否簡單居中或邊緣對齊?}
    F -- 是 --> G[可考慮FrameLayout或ConstraintLayout]
    F -- 否 --> H[評估性能後選擇ConstraintLayout]
    E --> I[推薦作為默認佈局容器]

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <EditText
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="3"
        android:hint="輸入內容" />

    <Button
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="發送" />
</LinearLayout>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:text="主內容區" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="操作按鈕" />
</LinearLayout>

<!-- res/layout/header.xml -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <TextView
        android:id="@+id/tv_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="通用標題欄" />
</LinearLayout>

<!-- 主佈局中引用 -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <include layout="@layout/header" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="正文內容" />
</LinearLayout>

<!-- res/layout/content_block.xml -->
<merge xmlns:android="http://schemas.android.com/apk/res/android">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="區塊1" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="區塊2" />
</merge>

<ViewStub
    android:id="@+id/stub_error"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:inflatedId="@+id/error_layout"
    android:layout="@layout/error_message" />

// Java代碼中觸發加載
ViewStub stub = findViewById(R.id.stub_error);
if (hasError) {
    stub.inflate(); // 只在此刻才解析並創建視圖
}

<Button
    android:id="@+id/btn_submit"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="提交" />

Button btnSubmit = findViewById(R.id.btn_submit);
btnSubmit.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(this, "表單已提交", Toast.LENGTH_SHORT).show();
    }
});

btnSubmit.setOnClickListener(v -> 
    Toast.makeText(this, "提交成功", Toast.LENGTH_SHORT).show());

<Button
    android:onClick="onSubmitClick"
    android:text="提交" />

public void onSubmitClick(View view) {
    // 處理點擊
}

<EditText
    android:id="@+id/et_email"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="請輸入郵箱"
    android:inputType="textEmailAddress"
    android:imeOptions="actionDone" />

EditText etEmail = findViewById(R.id.et_email);
String email = etEmail.getText().toString();

if (Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
    // 郵箱格式合法
} else {
    etEmail.setError("請輸入有效的郵箱地址");
}

InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(etEmail.getWindowToken(), 0);

<ImageView
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:src="@drawable/ic_logo"
    android:scaleType="centerCrop" />

implementation 'com.github.bumptech.glide:glide:4.15.1'

Glide.with(context)
     .load("https://example.com/image.jpg")
     .placeholder(R.drawable.ic_placeholder)
     .error(R.drawable.ic_error)
     .into(imageView);

ArrayAdapter<String> adapter = new ArrayAdapter<>(this,
    android.R.layout.simple_list_item_1, dataList);

ListView listView = findViewById(R.id.list_view);
listView.setAdapter(adapter);

static class ViewHolder {
    TextView tvTitle;
    ImageView ivIcon;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        convertView = LayoutInflater.from(context).inflate(R.layout.item_list, parent, false);
        holder = new ViewHolder();
        holder.tvTitle = convertView.findViewById(R.id.tv_title);
        holder.ivIcon = convertView.findViewById(R.id.iv_icon);
        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }

    Item item = getItem(position);
    holder.tvTitle.setText(item.getTitle());
    holder.ivIcon.setImageResource(item.getIconRes());

    return convertView;
}

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

RecyclerView recyclerView = findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(new MyItemAdapter(dataList));

GridLayoutManager layoutManager = new GridLayoutManager(this, 2);
recyclerView.setLayoutManager(layoutManager);

<androidx.cardview.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:cardCornerRadius="8dp"
    app:cardElevation="4dp"
    app:contentPadding="16dp"
    android:layout_margin="8dp">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="這是一個卡片" />

</androidx.cardview.widget.CardView>

<GridLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:columnCount="2"
    android:useDefaultMargins="true">

    <!-- 多個CardView放入 -->

</GridLayout>

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
</style>

<style name="TextAppearance.Title" parent="TextAppearance.AppCompat.Title">
    <item name="android:textSize">20sp</item>
    <item name="android:textColor">@color/dark_gray</item>
</style>

<TextView
    style="@style/TextAppearance.Title"
    android:text="標題文本" />

implementation 'com.google.android.material:material:1.9.0'

<style name="AppTheme" parent="Theme.MaterialComponents.DayNight">
    ...
</style>

res/
  values/styles.xml          # 默認主題
  values-night/styles.xml    # 夜間主題

<resources>
    <style name="AppTheme" parent="Theme.MaterialComponents.DayNight">
        <item name="android:windowBackground">@color/black</item>
        <item name="android:textColor">@color/white</item>
    </style>
</resources>

AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);

// 獲取默認的SharedPreferences實例
SharedPreferences prefs = getSharedPreferences("user_prefs", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();

// 存儲數據
editor.putBoolean("is_logged_in", true);
editor.putString("username", "alice_2024");
editor.putInt("theme_mode", 2);
editor.apply(); // 異步提交，推薦用於非關鍵寫入

boolean isLoggedIn = prefs.getBoolean("is_logged_in", false);
String username = prefs.getString("username", "guest");
int themeMode = prefs.getInt("theme_mode", 1);

graph TD
    A[開始] --> B[調用getSharedPreferences]
    B --> C[獲取Editor對象]
    C --> D[調用putXxx方法設置值]
    D --> E[調用apply或commit]
    E --> F{是否主線程?}
    F -- apply --> G[異步提交到磁盤]
    F -- commit --> H[同步寫入並返回結果]
    G --> I[結束]
    H --> I

try (FileOutputStream fos = openFileOutput("notes.txt", Context.MODE_PRIVATE)) {
    String data = "今天完成了項目文檔撰寫";
    fos.write(data.getBytes(StandardCharsets.UTF_8));
} catch (IOException e) {
    Log.e("FileIO", "寫入失敗", e);
}

try (FileInputStream fis = openFileInput("notes.txt")) {
    byte[] buffer = new byte[fis.available()];
    fis.read(buffer);
    String content = new String(buffer, StandardCharsets.UTF_8);
    Log.d("FileRead", content);
} catch (IOException e) {
    Log.e("FileIO", "讀取失敗", e);
}

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

ContentValues values = new ContentValues();
values.put(MediaStore.Downloads.DISPLAY_NAME, "report.pdf");
values.put(MediaStore.Downloads.MIME_TYPE, "application/pdf");
values.put(MediaStore.Downloads.IS_PENDING, 1);

Uri uri = getContentResolver().insert(MediaStore.Downloads.EXTERNAL_CONTENT_URI, values);

if (uri != null) {
    try (OutputStream os = getContentResolver().openOutputStream(uri)) {
        byte[] pdfData = generatePdfBytes();
        os.write(pdfData);
    } catch (IOException e) {
        Log.e("MediaStore", "保存失敗", e);
    }

    // 完成寫入
    values.clear();
    values.put(MediaStore.Downloads.IS_PENDING, 0);
    getContentResolver().update(uri, values, null, null);
}

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "app.db";
    private static final int DB_VERSION = 1;

    public DatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_TABLE_USERS = "CREATE TABLE users (" +
                "id INTEGER PRIMARY KEY AUTOINCREMENT," +
                "name TEXT NOT NULL," +
                "email TEXT UNIQUE," +
                "age INTEGER" +
                ")";
        db.execSQL(CREATE_TABLE_USERS);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS users");
        onCreate(db);
    }
}

DatabaseHelper helper = new DatabaseHelper(this);
SQLiteDatabase db = helper.getWritableDatabase();

ContentValues values = new ContentValues();
values.put("name", "Bob");
values.put("email", "bob@example.com");
values.put("age", 30);

long rowId = db.insert("users", null, values);
if (rowId != -1) {
    Log.d("DB", "插入成功，行ID：" + rowId);
}

Cursor cursor = db.query("users", null, null, null, null, null, null);
while (cursor.moveToNext()) {
    int id = cursor.getInt(cursor.getColumnIndexOrThrow("id"));
    String name = cursor.getString(cursor.getColumnIndexOrThrow("name"));
    String email = cursor.getString(cursor.getColumnIndexOrThrow("email"));
    int age = cursor.getInt(cursor.getColumnIndexOrThrow("age"));
    Log.d("User", String.format("%d: %s (%s), %d歲", id, name, email, age));
}
cursor.close();

db.beginTransaction();
try {
    for (int i = 0; i < 1000; i++) {
        ContentValues v = new ContentValues();
        v.put("name", "User" + i);
        v.put("email", "user" + i + "@test.com");
        v.put("age", 20 + (i % 50));
        db.insert("users", null, v);
    }
    db.setTransactionSuccessful(); // 標記事務成功
} finally {
    db.endTransaction(); // 提交或回滾
}

graph LR
    A[創建DatabaseHelper] --> B[調用getWritableDatabase]
    B --> C{是否首次運行?}
    C -- 是 --> D[執行onCreate建表]
    C -- 否 --> E[打開現有數據庫]
    D --> F
    E --> F[執行CRUD操作]
    F --> G[使用ContentValues封裝數據]
    G --> H[調用insert/update/delete/query]
    H --> I[涉及多條語句?]
    I -- 是 --> J[開啓事務 beginTransaction]
    J --> K[批量操作]
    K --> L[setTransactionSuccessful]
    L --> M[endTransaction]
    I -- 否 --> N[直接執行]
    N --> O[關閉Cursor和DB連接]

URL url = new URL("https://api.example.com/users/1");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);  // 連接超時：5秒
conn.setReadTimeout(10000);    // 讀取超時：10秒
conn.setRequestProperty("Accept", "application/json");

int responseCode = conn.getResponseCode();
if (responseCode == 200) {
    InputStream is = conn.getInputStream();
    String result = convertStreamToString(is);
    Log.d("HTTP", "響應：" + result);
} else {
    Log.e("HTTP", "請求失敗：" + responseCode);
}
conn.disconnect();

private String convertStreamToString(InputStream is) throws IOException {
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();
    String line;
    while ((line = reader.readLine()) != null) {
        sb.append(line).append("\n");
    }
    return sb.toString();
}

implementation 'com.squareup.okhttp3:okhttp:4.12.0'

OkHttpClient client = new OkHttpClient();

Request request = new Request.Builder()
        .url("https://api.example.com/posts")
        .header("Authorization", "Bearer token123")
        .build();

client.newCall(request).enqueue(new Callback() {
    @Override
    public void onFailure(Call call, IOException e) {
        Log.e("OkHttp", "請求失敗", e);
    }

    @Override
    public void onResponse(Call call, Response response) throws IOException {
        if (response.isSuccessful()) {
            String responseBody = response.body().string();
            Log.d("OkHttp", "數據：" + responseBody);
        }
    }
});

MediaType JSON = MediaType.get("application/json; charset=utf-8");
String jsonBody = "{\"title\":\"New Post\",\"content\":\"Hello World\"}";

RequestBody body = RequestBody.create(jsonBody, JSON);
Request request = new Request.Builder()
        .url("https://api.example.com/posts")
        .post(body)
        .build();

client.newCall(request).enqueue(...);

OkHttpClient client = new OkHttpClient.Builder()
        .connectTimeout(10, TimeUnit.SECONDS)
        .readTimeout(30, TimeUnit.SECONDS)
        .writeTimeout(30, TimeUnit.SECONDS)
        .retryOnConnectionFailure(true)
        .cache(new Cache(getCacheDir(), 10 * 1024 * 1024)) // 10MB 緩存
        .build();

class AuthInterceptor implements Interceptor {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request original = chain.request();
        Request authorized = original.newBuilder()
                .header("Authorization", "Bearer " + getToken())
                .header("Client-Version", BuildConfig.VERSION_NAME)
                .build();
        return chain.proceed(authorized);
    }
}

// 註冊
OkHttpClient client = new OkHttpClient.Builder()
        .addInterceptor(new AuthInterceptor())
        .build();

CookieJar cookieJar = new CookieJar() {
    private final HashMap<HttpUrl, List<Cookie>> cookieStore = new HashMap<>();

    @Override
    public void saveFromResponse(HttpUrl url, List<Cookie> cookies) {
        cookieStore.put(url, cookies);
    }

    @Override
    public List<Cookie> loadForRequest(HttpUrl url) {
        List<Cookie> cookies = cookieStore.get(url);
        return cookies != null ? cookies : new ArrayList<>();
    }
};

OkHttpClient client = new OkHttpClient.Builder()
        .cookieJar(cookieJar)
        .build();

// ⚠️ 僅用於調試，禁止上線
TrustManager[] trustAllCerts = new TrustManager[]{
    new X509TrustManager() {
        public java.security.cert.X509Certificate[] getAcceptedIssuers() { return null; }
        public void checkClientTrusted(java.security.cert.X509Certificate[] certs, String authType) {}
        public void checkServerTrusted(java.security.cert.X509Certificate[] certs, String authType) {}
    }
};

SSLContext sc = SSLContext.getInstance("SSL");
sc.init(null, trustAllCerts, new java.security.SecureRandom());
client.newBuilder().sslSocketFactory(sc.getSocketFactory(), (X509TrustManager)trustAllCerts[0]).build();

// 示例：在代碼中添加結構化日誌
private static final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d(TAG, "Activity created with savedInstanceState: " + (savedInstanceState != null));
    Log.i(TAG, "App version: " + BuildConfig.VERSION_NAME);
}

android {
    compileSdk 34

    defaultConfig {
        applicationId "com.example.myapp"
        minSdk 21
        targetSdk 34
        versionCode 101
        versionName "1.0.1"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        debug {
            minifyEnabled false
            applicationIdSuffix ".debug"
            versionNameSuffix "-dev"
        }
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    flavorDimensions 'version'
    productFlavors {
        free {
            dimension 'version'
            applicationIdSuffix '.free'
            versionNameSuffix '-free'
        }
        premium {
            dimension 'version'
            applicationIdSuffix '.premium'
            versionNameSuffix '-pro'
        }
    }
}

dependencies {
    implementation 'androidx.appcompat:appcompat:1.6.1'
    implementation 'com.google.android.material:material:1.10.0'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}

task generateBuildInfo(type: Exec) {
    commandLine 'sh', '-c', 'echo "BUILD_TIME=`date`" > src/main/assets/build_info.prop"'
}
preBuild.dependsOn generateBuildInfo

public class CalculatorTest {
    private Calculator calculator;

    @Before
    public void setUp() {
        calculator = new Calculator();
    }

    @Test
    public void testAdd_TwoPositiveNumbers_ReturnsCorrectSum() {
        assertEquals(5, calculator.add(2, 3));
    }

    @Test(expected = IllegalArgumentException.class)
    public void testDivide_ByZero_ThrowsException() {
        calculator.divide(10, 0);
    }
}

@RunWith(AndroidJUnit4.class)
public class MainActivityTest {

    @Rule
    public ActivityScenarioRule<MainActivity> activityRule =
            new ActivityScenarioRule<>(MainActivity.class);

    @Test
    public void clickButton_ShowsToast() {
        onView(withId(R.id.btn_greet)).perform(click());
        onView(withText("Hello!")).inRoot(new ToastMatcher())
                .check(matches(isDisplayed()));
    }
}

androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'

private static final int REQUEST_LOCATION_PERMISSION = 1001;

if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
        != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this,
            new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
            REQUEST_LOCATION_PERMISSION);
} else {
    startLocationService();
}

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == REQUEST_LOCATION_PERMISSION) {
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            startLocationService();
        } else {
            Toast.makeText(this, "位置權限被拒絕", Toast.LENGTH_SHORT).show();
        }
    }
}

graph TD
    A[編寫Java代碼] --> B[XML佈局設計]
    B --> C[Gradle構建APK]
    C --> D[安裝到本機]
    D --> E[測試運行]
    E --> F{是否通過?}
    F -- 否 --> A
    F -- 是 --> G[發佈到應用市場]