Java technology stack: from beginner to proficient

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

public class Animal {
    private String name;
    
    public Animal(String name) {
        this.name = name;
    }
    
    public void sayHello() {
        System.out.println("Hello, I am " + name);
    }
}

public class Dog extends Animal {
    public Dog(String name) {
        super(name);
    }
    
    public void bark() {
        System.out.println("Woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog("Tommy");
        dog.sayHello();
        dog.bark();
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            int result = divide(10, 0);
            System.out.println("Result: " + result);
        } catch (ArithmeticException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
    
    public static int divide(int a, int b) throws ArithmeticException {
        if (b == 0) {
            throw new ArithmeticException("Divisor cannot be zero");
        }
        return a / b;
    }
}

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }
    }
}

public class MyThread extends Thread {
    private String name;
    
    public MyThread(String name) {
        this.name = name;
    }
    
    public void run() {
        for (int i = 0; i < 5; i++) {
            System.out.println(name + " " + i);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread thread1 = new MyThread("Thread 1");
        MyThread thread2 = new MyThread("Thread 2");
        thread1.start();
        thread2.start();
    }
}

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try (BufferedReader reader = new BufferedReader(new FileReader("input.txt"));
             BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                writer.write(line);
                writer.newLine();
            }
            System.out.println("File copied successfully");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class Main {
    public static void main(String[] args) {
        try (Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydatabase", "username", "password");
             PreparedStatement statement = connection.prepareStatement("SELECT * FROM users");
             ResultSet resultSet = statement.executeQuery()) {
            while (resultSet.next()) {
                String username = resultSet.getString("username");
                String email = resultSet.getString("email");
                System.out.println("Username: " + username + ", Email: " + email);
            }
        } catch (SQLException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(8000)) {
            System.out.println("Server started");
            while (true) {
                Socket socket = serverSocket.accept();
                new Thread(() -> handleClient(socket)).start();
            }
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
    
    private static void handleClient(Socket socket) {
        // 处理客户端请求的逻辑
    }
}

public class Client {
    public static void main(String[] args) {
        try (Socket socket = new Socket("localhost", 8000)) {
            // 发送请求与服务器通信的逻辑
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

public class HelloWorldServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<body>");
        out.println("<h1>Hello, world!</h1>");
        out.println("</body>");
        out.println("</html>");
    }
}