什么是“松耦合”？请提供示例

Question

我似乎无法理解“松散耦合”的概念。我想这不利于单词“宽松”通常有负面的含义，所以我总是忘了松耦合是一个很好的事情。

有人可以显示说明此概念的“之前”和“之后”代码（或伪代码）吗？

Answer 1

考虑一个简单的购物车应用程序，该应用程序使用CartContents类来跟踪购物车中的项目，并使用Order类来处理购买。订单需要确定购物车中内容的总价值，它可能会像这样：紧密耦合示例：public class CartEntry{&nbsp; &nbsp; public float Price;&nbsp; &nbsp; public int Quantity;}public class CartContents{&nbsp; &nbsp; public CartEntry[] items;}public class Order{&nbsp; &nbsp; private CartContents cart;&nbsp; &nbsp; private float salesTax;&nbsp; &nbsp; public Order(CartContents cart, float salesTax)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; this.cart = cart;&nbsp; &nbsp; &nbsp; &nbsp; this.salesTax = salesTax;&nbsp; &nbsp; }&nbsp; &nbsp; public float OrderTotal()&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; float cartTotal = 0;&nbsp; &nbsp; &nbsp; &nbsp; for (int i = 0; i < cart.items.Length; i++)&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; cartTotal += cart.items[i].Price * cart.items[i].Quantity;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; cartTotal += cartTotal*salesTax;&nbsp; &nbsp; &nbsp; &nbsp; return cartTotal;&nbsp; &nbsp; }}注意OrderTotal方法（以及Order类）如何取决于CartContents和CartEntry类的实现细节。如果我们试图更改此逻辑以允许折扣，则可能必须更改所有三个类别。另外，如果我们更改为使用List集合来跟踪项目，则也必须更改Order类。现在，这是一种执行相同操作的更好方法：较少耦合的示例：public class CartEntry{&nbsp; &nbsp; public float Price;&nbsp; &nbsp; public int Quantity;&nbsp; &nbsp; public float GetLineItemTotal()&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; return Price * Quantity;&nbsp; &nbsp; }}public class CartContents{&nbsp; &nbsp; public CartEntry[] items;&nbsp; &nbsp; public float GetCartItemsTotal()&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; float cartTotal = 0;&nbsp; &nbsp; &nbsp; &nbsp; foreach (CartEntry item in items)&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; cartTotal += item.GetLineItemTotal();&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return cartTotal;&nbsp; &nbsp; }}public class Order{&nbsp; &nbsp; private CartContents cart;&nbsp; &nbsp; private float salesTax;&nbsp; &nbsp; public Order(CartContents cart, float salesTax)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; this.cart = cart;&nbsp; &nbsp; &nbsp; &nbsp; this.salesTax = salesTax;&nbsp; &nbsp; }&nbsp; &nbsp; public float OrderTotal()&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; return cart.GetCartItemsTotal() * (1.0f + salesTax);&nbsp; &nbsp; }}特定于购物车订单项，购物车集合或订单的实现的逻辑仅限于该类。因此，我们可以更改任何这些类的实现，而不必更改其他类。我们可以通过改进设计，引入接口等来进一步消除这种耦合，但我认为您已经明白了。

Answer 2

iPod，iPad等许多集成产品（尤其是Apple的产品）就是紧密耦合的一个很好的例子：一旦电池耗尽，您最好购买新设备，因为电池已焊接固定并且不会松动，因此更换非常容易昂贵。松散耦合的播放器可以轻松更换电池。这同样也适用于软件开发：它通常是（多）最好有松耦合代码，方便扩展和替换（并且使各个部件更容易理解）。但是，在极少数情况下，紧密耦合可能是有利的，因为几个模块的紧密集成可以实现更好的优化。