Android/Java中创建类实例的各种模式实例代码

// 基本语法
ClassName object = new ClassName(arguments);

// 示例
User user = new User("Alice", 25);
TextView textView = new TextView(context);

// 创建基础UI组件
TextView textView = new TextView(context);
Button button = new Button(context);

// 创建数据对象
Intent intent = new Intent(context, MainActivity.class);
Bundle bundle = new Bundle();

public class Connection {
    private String url;
    
    private Connection(String url) {
        this.url = url;
    }
    
    // 静态工厂方法
    public static Connection create(String url) {
        validateUrl(url); // 添加验证逻辑
        return new Connection(url);
    }
    
    // 有名称的工厂方法
    public static Connection createSecureConnection() {
        return new Connection("https://secure.example.com");
    }
}

// 使用
Connection conn = Connection.create("https://api.example.com");

// Intent 工厂方法
Intent chooserIntent = Intent.createChooser(shareIntent, "Share via");

// Bitmap 工厂方法
Bitmap bitmap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);

// Uri 解析
Uri uri = Uri.parse("content://com.example.provider/data");

public class AlertDialogConfig {
    private final String title;
    private final String message;
    private final boolean cancelable;
    
    private AlertDialogConfig(Builder builder) {
        this.title = builder.title;
        this.message = builder.message;
        this.cancelable = builder.cancelable;
    }
    
    public static class Builder {
        private String title;
        private String message;
        private boolean cancelable = true;
        
        public Builder setTitle(String title) {
            this.title = title;
            return this;
        }
        
        public Builder setMessage(String message) {
            this.message = message;
            return this;
        }
        
        public Builder setCancelable(boolean cancelable) {
            this.cancelable = cancelable;
            return this;
        }
        
        public AlertDialogConfig build() {
            return new AlertDialogConfig(this);
        }
    }
}

// 使用
AlertDialogConfig config = new AlertDialogConfig.Builder()
    .setTitle("Warning")
    .setMessage("Are you sure?")
    .setCancelable(false)
    .build();

// Notification 建造者
Notification notification = new NotificationCompat.Builder(context, "channel_id")
    .setContentTitle("Title")
    .setContentText("Message")
    .setSmallIcon(R.drawable.ic_notification)
    .build();

// Retrofit 建造者
Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("https://api.example.com/")
    .addConverterFactory(GsonConverterFactory.create())
    .build();

// 双重检查锁实现
public class AppManager {
    private static volatile AppManager instance;
    private final Context appContext;
    
    private AppManager(Context context) {
        this.appContext = context.getApplicationContext();
    }
    
    public static AppManager getInstance(Context context) {
        if (instance == null) {
            synchronized (AppManager.class) {
                if (instance == null) {
                    instance = new AppManager(context);
                }
            }
        }
        return instance;
    }
}

// 静态内部类实现（推荐）
public class DatabaseHelper {
    private DatabaseHelper() {}
    
    private static class Holder {
        static final DatabaseHelper INSTANCE = new DatabaseHelper();
    }
    
    public static DatabaseHelper getInstance() {
        return Holder.INSTANCE;
    }
}

// Application 类本身就是单例
public class MyApp extends Application {
    private static MyApp instance;
    
    @Override
    public void onCreate() {
        super.onCreate();
        instance = this;
    }
    
    public static MyApp getInstance() {
        return instance;
    }
}

// 使用单例
ImageLoader.getInstance().loadImage(url, imageView);

// 手动依赖注入
public class UserRepository {
    private final ApiService apiService;
    
    public UserRepository(ApiService apiService) {
        this.apiService = apiService; // 依赖注入
    }
}

// 使用 Dagger/Hilt
@Module
@InstallIn(SingletonComponent.class)
public class NetworkModule {
    @Provides
    @Singleton
    public Retrofit provideRetrofit() {
        return new Retrofit.Builder()
            .baseUrl("https://api.example.com/")
            .addConverterFactory(GsonConverterFactory.create())
            .build();
    }
}

@AndroidEntryPoint
public class MainActivity extends AppCompatActivity {
    @Inject
    Retrofit retrofit; // 自动注入
}

// Hilt 注入 ViewModel
@HiltViewModel
public class MainViewModel extends ViewModel {
    private final UserRepository repository;
    
    @Inject
    public MainViewModel(UserRepository repository) {
        this.repository = repository;
    }
}

// Activity 中使用
@AndroidEntryPoint
public class MainActivity extends AppCompatActivity {
    @Inject
    MainViewModel viewModel;
}

public interface ThemeFactory {
    Button createButton();
    TextView createTextView();
    Dialog createDialog();
}

public class LightThemeFactory implements ThemeFactory {
    @Override
    public Button createButton() {
        Button button = new Button(context);
        button.setBackgroundColor(Color.WHITE);
        return button;
    }
    // 其他方法...
}

public class DarkThemeFactory implements ThemeFactory {
    @Override
    public Button createButton() {
        Button button = new Button(context);
        button.setBackgroundColor(Color.BLACK);
        return button;
    }
    // 其他方法...
}

public class UserProfile implements Cloneable {
    private String username;
    private Map<String, Object> preferences;
    
    public UserProfile(String username) {
        this.username = username;
        this.preferences = loadPreferences(); // 耗时操作
    }
    
    @Override
    public UserProfile clone() {
        try {
            UserProfile cloned = (UserProfile) super.clone();
            cloned.preferences = new HashMap<>(this.preferences); // 深拷贝
            return cloned;
        } catch (CloneNotSupportedException e) {
            throw new AssertionError();
        }
    }
}

// 使用
UserProfile original = new UserProfile("user123");
UserProfile copy = original.clone(); // 比 new 快很多

public class ObjectFactory {
    public static <T> T createInstance(String className) {
        try {
            Class<?> clazz = Class.forName(className);
            return (T) clazz.newInstance();
        } catch (Exception e) {
            throw new RuntimeException("创建实例失败", e);
        }
    }
}

// 使用
String className = "com.example.MyClass";
MyClass obj = ObjectFactory.createInstance(className);