如何在面向对象设计中合理放置新功能方法

public class Order {
    private String orderId;
    private OrderStatus status;
    // ... 其他订单属性

    public ProcessingResult place() {
        // 执行下单逻辑，如状态变更、库存扣减、生成处理结果等
        if (this.status == OrderStatus.NEW) {
            this.status = OrderStatus.PLACED;
            System.out.println("订单 " + orderId + " 已成功下单。");
            return new ProcessingResult(true, "订单下单成功。");
        } else {
            System.out.println("订单 " + orderId + " 状态不正确，无法下单。");
            return new ProcessingResult(false, "订单状态不正确。");
        }
    }
}

public class ProcessingResult {
    private boolean success;
    private String message;

    public ProcessingResult(boolean success, String message) {
        this.success = success;
        this.message = message;
    }

    // ... getter方法
}

public class B {
    private String name;
    private int value;

    private B(String name, int value) { // 私有构造器，强制通过工厂方法创建
        this.name = name;
        this.value = value;
    }

    public static B create(Parameters parameters) {
        // 根据parameters的属性创建B的实例
        if (parameters.isValid()) {
            return new B(parameters.getName(), parameters.getValue());
        } else {
            throw new IllegalArgumentException("无效的创建参数。");
        }
    }
    // ... getter方法
}

public class Parameters {
    private String name;
    private int value;

    public Parameters(String name, int value) {
        this.name = name;
        this.value = value;
    }

    public boolean isValid() {
        return name != null && !name.isEmpty() && value > 0;
    }
    // ... getter方法
}

public class BFactory {
    public static B createFromParameters(Parameters parameters) {
        if (parameters.isValid()) {
            return new B(parameters.getName(), parameters.getValue());
        } else {
            throw new IllegalArgumentException("无效的创建参数。");
        }
    }
}

public class FooUseCase {
    // 依赖注入所需的领域服务或仓储
    private final SomeDomainService domainService;
    private final AnotherRepository anotherRepository;

    public FooUseCase(SomeDomainService domainService, AnotherRepository anotherRepository) {
        this.domainService = domainService;
        this.anotherRepository = anotherRepository;
    }

    public FooUseCaseResult execute(FooUseCaseParameters parameters) {
        // 1. 验证参数
        if (!parameters.isValid()) {
            return new FooUseCaseResult(false, "参数无效。");
        }

        // 2. 根据参数从仓储获取或创建领域对象
        DomainObjectA a = anotherRepository.findById(parameters.getAId());
        if (a == null) {
            return new FooUseCaseResult(false, "找不到相关对象A。");
        }

        // 3. 执行核心业务逻辑，可能调用领域服务或A的方法
        boolean success = domainService.performAction(a, parameters.getData());

        // 4. 根据结果构建FooUseCaseResult
        if (success) {
            return new FooUseCaseResult(true, "用例执行成功。", a.getCurrentState());
        } else {
            return new FooUseCaseResult(false, "用例执行失败。", a.getCurrentState());
        }
    }
}

public class FooUseCaseParameters {
    private String aId;
    private String data;
    // ... 构造器、getter、isValid方法
}

public class FooUseCaseResult {
    private boolean success;
    private String message;
    private String finalStateOfA;
    // ... 构造器、getter
}