Java에서 데이터 및 경쟁 조건을 형성하기 위한 동시 액세스를 처리하는 방법은 무엇입니까?

public class User {
    private String username;
    private String password;
    
    // 省略构造函数和getter/setter方法
}

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;

public class UserService {
    private Map<String, User> users = new HashMap<>();
    private AtomicInteger count = new AtomicInteger(0);
    
    public boolean registerUser(String username, String password) {
        // 检查账号是否已被注册
        if (users.containsKey(username)) {
            return false;
        }
        
        // 模拟注册需要一定时间
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        // 创建新用户并添加到注册用户列表
        User user = new User(username, password);
        users.put(username, user);
        count.incrementAndGet();
        
        return true;
    }
    
    public int getUserCount() {
        return count.get();
    }
}

public class Main {
    public static void main(String[] args) {
        final UserService userService = new UserService();
        
        // 创建10个模拟用户注册的线程
        for (int i = 0; i < 10; i++) {
            final int index = i;
            new Thread(() -> {
                String username = "user" + index;
                String password = "password" + index;
                
                boolean success = userService.registerUser(username, password);
                if (success) {
                    System.out.println("User " + username + " registered successfully!");
                    System.out.println("Total registered user count: " + userService.getUserCount());
                } else {
                    System.out.println("User " + username + " registration failed!");
                }
            }).start();
        }
    }
}