public enum Singleton {
    INSTANCE;
    public void doSomething() {}
}

public class UserFactory {
    public static User createUser(String type) {
        return switch (type) {
            case "admin" -> new AdminUser();
            case "guest" -> new GuestUser();
            default -> new RegularUser();
        };
    }
}

User user = User.builder()
    .name("张三")
    .age(25)
    .build();

List<String> names = users.stream()
    .filter(u -> u.getAge() > 18)
    .map(User::getName)
    .collect(Collectors.toList());

try {
    // 业务逻辑
} catch (SpecificException e) {
    log.error("Error: {}", e.getMessage(), e);
    throw new BusinessException("操作失败");
} finally {
    // 清理资源
}

ExecutorService executor = Executors.newFixedThreadPool(10);
executor.submit(() -> {
    // 异步任务
});

Optional<User> user = userRepository.findById(id);
return user.orElseThrow(() -> new NotFoundException());