Java | Фишки и трюки

public class MyClass implements Cloneable {
    private int value;
    
    // Конструкторы и методы класса
    
    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

Frame frame = new Frame("Название окна");
frame.setSize(400, 300);
frame.setVisible(true);

JFrame frame = new JFrame("Название окна");
frame.setSize(400, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);

Button button = new Button("Нажми меня");
frame.add(button);

JButton button = new JButton("Нажми меня");
frame.add(button);

TextField textField = new TextField("Введите текст");
frame.add(textField);

JTextField textField = new JTextField("Введите текст");
frame.add(textField);

button.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        System.out.println("Кнопка была нажата");
    }
});

Tomcat tomcat = new Tomcat();
tomcat.setPort(8080);
tomcat.addWebapp("/myapp", new File("src/main/webapp/").getAbsolutePath());
tomcat.addServlet("/myservlet", "MyServlet", MyServlet.class.getName());
tomcat.start();

<dependency>
 <groupId>org.apache.tomcat.embed</groupId>
 <artifactId>tomcat-embed-core</artifactId>
 <version>11.0.0-M18</version>
</dependency>
<dependency>
 <groupId>org.apache.tomcat.embed</groupId>
 <artifactId>tomcat-embed-jasper</artifactId>
 <version>11.0.0-M18</version>
</dependency>
<dependency>
 <groupId>org.apache.tomcat</groupId>
 <artifactId>tomcat-jasper</artifactId>
 <version>11.0.0-M18</version>
</dependency>
<dependency>
 <groupId>org.apache.tomcat</groupId>
 <artifactId>tomcat-jasper-el</artifactId>
 <version>11.0.0-M18</version>
</dependency>
<dependency>
 <groupId>org.apache.tomcat</groupId>
 <artifactId>tomcat-jsp-api</artifactId>
 <version>11.0.0-M18</version>
</dependency>

class Cache {
  private static int sum = 0;
    
  static {
    initializeIfNecessary();
  }
    
  public static int getSum() {
    initializeIfNecessary();
    return sum;
  }
    
  private static boolean initialized = false;
    
  private static synchronized void initializeIfNecessary() {
    if (!initialized) {
      for (int i = 0; i < 5; i++)
        sum += i;
      initialized = true;
    }
  }
}

class Client {
  public static void main(String[] args) {
    System.out.println(Cache.getSum());
  }
}

import org.apache.poi.ss.usermodel.*;

public class ExcelWriter {
    public static void main(String[] args) {
        Workbook wb = new XSSFWorkbook();
        Sheet sheet = wb.createSheet("Sheet1");

        Row headerRow = sheet.createRow(0);
        Cell headerCell = headerRow.createCell(0);
        headerCell.setCellValue("Name");

        Row dataRow = sheet.createRow(1);
        Cell dataCell = dataRow.createCell(0);
        dataCell.setCellValue("John Doe");

        try (FileOutputStream fileOut = new FileOutputStream("workbook.xlsx")) {
            wb.write(fileOut);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@RepositoryRestResource(path = "users")
public interface UserRepository extends JpaRepository<User, Long> {
    
}

GET /users - Получить всех пользователей
POST /users - Создать нового пользователя
GET /users/{id} - Получить пользователя по ID
PUT /users/{id} - Обновить пользователя
DELETE /users/{id} - Удалить пользователя

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet("http://example.com");
CloseableHttpResponse response = httpClient.execute(httpGet);

httpGet.setHeader("Content-Type", "application/json");

StringEntity entity = new StringEntity("{\"key\": \"value\"}");
httpPost.setEntity(entity);

int statusCode = response.getStatusLine().getStatusCode();

String responseBody = EntityUtils.toString(response.getEntity());

class Point {
  private final int x, y;
  private final String name;

  Point(int x, int y) {
    this.x = x;
    this.y = y;
    name = makeName();
  }

  protected String makeName() {
    return "[" + x + "," + y + "]";
  }

  public final String toString() {
    return name;
  }
}

public class ColorPoint extends Point {
  private final String color;

  ColorPoint(int x, int y, String color) {
    super(x, y);
    this.color = color;
  }

  protected String makeName() {
    return super.makeName() + ":" + color;
  }

  public static void main(String[] args) {
    System.out.println(new ColorPoint(4, 2, "red"));
  }
}

File file = new File("test.txt");
String content = FileUtils.readFileToString(file, StandardCharsets.UTF_8);
System.out.println(content);

InputStream input = new FileInputStream("input.txt");
OutputStream output = new FileOutputStream("output.txt");
IOUtils.copy(input, output);
input.close();
output.close();

File directory = new File("C:/my_folder");
String[] extensions = {"txt", "xml"};
List<File> files = (List<File>) FileUtils.listFiles(directory, extensions, true);
for (File file : files) {
    System.out.println(file.getName());
}

String filename = "example.txt";
String extension = FilenameUtils.getExtension(filename);
System.out.println(extension);