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

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        System.out.println("Input q to exit.");
        try (Scanner input = new Scanner(System.in)) {
            while (true) {
                String line = input.nextLine();
                if (line.equalsIgnoreCase("q")) {
                    break;
                }
                System.out.println("echo:" + line);
            }
        }
        System.out.println("exited.");
    }
}

import java.net.ServerSocket;
import java.net.Socket;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.io.IOException;

public class Main {

    public static void main(String[] args) {
        new Thread(Main::serverSocket).start();

        System.out.println("Please input:");
        try (var s = new Socket("127.0.0.1", 12345);
                var out = new PrintWriter(s.getOutputStream(), true);
                var in = new BufferedReader(new InputStreamReader(s.getInputStream()));
                var stdIn = new BufferedReader(new InputStreamReader(System.in))) {
            String userInput;
            while ((userInput = stdIn.readLine()) != null) {
                out.println(userInput);
                System.out.println("Echo: " + in.readLine());
            }
        } catch (IOException e) {
            System.err.println(e);
        }
    }

    public static void serverSocket() {
        try (var ss = new ServerSocket(12345); var s = ss.accept();
                var out = new PrintWriter(s.getOutputStream(), true);
                var in = new BufferedReader(new InputStreamReader(s.getInputStream()))) {
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                out.println(inputLine);
            }
        } catch (IOException e) {
            System.err.println(e);
        }
    }
}

public static void main(String[] args) {
  // implementation 'mysql:mysql-connector-java:8.0.27'
  String url = "jdbc:mysql://127.0.0.1:3306/db-name";
  String user = "root", password = "1";
  try (Connection conn = DriverManager.getConnection(url, user, password);
        Statement sta = conn.createStatement()) {
    ResultSet rs = sta.executeQuery("select 'Hello, World!'");
    rs.next(); // while (rs.next()) { System.out.println(rs.getObject("Name")); }
    System.out.println(rs.getObject(1));
  } catch (SQLException ex) {
    System.err.println(ex);
  }
}

import java.util.concurrent.Flow;
import java.util.concurrent.SubmissionPublisher;
import java.util.stream.IntStream;

public class Main {

    public static void main(String[] args) {

        try ( var pub = new SubmissionPublisher<Integer>()) {
            // consume方法订阅了内置ConsumerSubscriber
            // CompletableFuture<Void>返回值收集消费状态
            pub.consume(System.out::println);

            /* Or 自定义Subscriber(onNext方法进行业务处理) */
            pub.subscribe(new Flow.Subscriber<Integer>() {
                Flow.Subscription thisSub;
                @Override
                public void onSubscribe(Flow.Subscription subscription) {
                    thisSub = subscription;
                    thisSub.request(1); // 此处决定首批消费量
                }
                @Override
                public void onNext(Integer itemOrUrl) {
                    System.out.println(itemOrUrl);
                    // 业务处理 - consumer.accept(item);
                    thisSub.request(1); // 此处决定下批消费量
                }
                @Override public void onComplete() {}
                @Override public void onError(Throwable throwable) {}
            });

            IntStream.range(1, 600000).forEach(pub::submit);
        }

    }
}

public class Hi {

    public static void main(String[] args) {
        var f = new javax.swing.JFrame();
        f.setVisible(true); // 默认不显示JFrame窗体
        f.setSize(800, 600); // 默认只有标题栏而无内容区
        // 点关闭图标只会隐藏窗体，还需声明下程序的联动退出
        f.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);
        //getContentPane().add(new JButton("button")); // 添加控件至窗体
    }
}

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
public class Hi {

    public static void main(String[] args) {
        SpringApplication.run(Main.class, args);
    }
}

@RestController
class HelloWorld {

    @RequestMapping("/")
    public String helloworld() {
        return "Hello, World!";
    }
}

ObjectMapper objectMapper = new ObjectMapper();

简单数据绑定:

    //  绑定简单类型
    Integer age = objectMapper.readValue("1", int.class);
    System.out.println(age);

    //  绑定Map类型
    Map map = objectMapper.readValue("{\"name\":  \"Hello\"}", Map.class);
    System.out.println(map);

完全数据绑定(Java Bean)：

    ...