返回数据结构以显示信息 [英] Returning a Data Structure to Display information

问题描述

我在SESE上阅读了有关封装和吸气剂/吸气剂的此答案.假设我赞成使用不可变的类，因此，如果实现了setter，它将返回一个反映更改的新对象，例如:

I was reading this answer on SESE about encapsulation and getters/setters. Suppose I favor the use of immutable classes, so if a setter were implemented, it would return the a new object reflecting the change, for example:

//return a new Book reflecting the price change.
public Book updatePrice(double price){}

在链接中，答案建议我有一个称为 getDisplayinformation()的方法，该方法返回数据结构.

In the link, the answer suggested I have a method called getDisplayinformation() that returns a data structure.

(考虑一个由枚举，结构或无方法类索引的数组)

(think an array indexed by an enum, a struct, or a methodless class)

根据此建议，我该如何退还一本包含作者名单的书?

Following this advice how would I return a Book with a List of authors?

public final class Author{
    private final String id;
    private final String firstname;
    private final String lastname;
    //Constructor 
}
public final class Book{
    private String bookID;
    private final String title;
    private List<Author> authorsList;
    private double price;
    //Constructor
}

假设我想返回一个 Map< String，String> .

public Map<String,String> getDisplayinformation(){

    Map<String,String> displayMap = new HashMap<String,String>();
    display.put("BookTitle", title);
    display.put("ID", bookID); 
    display.put("Price", price.toString())
    //insert authorsList;
    return displayMap;
}

推荐答案

您引用的答案正确了一半.为字段提供吸气剂确实会破坏封装，因为它使调用者依赖于某些内部结构.

The answer you quote got half of it right. Providing getters for fields does break encapsulation, because it makes the caller dependent on some internal structure.

现在，返回一个地图，在此地图中，调用者需要知道键并知道该信息是什么，基本上与为该字段提供获取器没有什么不同.

Now, returning a map where the caller needs to know the keys and knows what that information is, is basically not different than providing a getter for that field.

面向对象试图告诉我们功能需要与数据捆绑在一起.因此， Book 必须具有某种方法来呈现 Book .我不会称其为 getDisplayInformation()，而是简称为 display().它可以返回某些内容，也可以使用相关的参数.

Object-orientation tries to tell us that the functionality needs to be bundled with the data. So, the Book has to have some method to present the Book. I would not call it getDisplayInformation(), rather simply display(). It can return something, and it can take relevant parameters too.

重点是， display()返回的任何内容都必须与演示文稿有关，而与书本无关.在那一刻，应该失去关于书籍的语义，否则呼叫者将紧密地联系在一起.

The point is, that anything returned by display() must be about the presentation, and must not be about the book. Semantics about being a book should be lost at that point, otherwise the caller will be tightly coupled.

因此，可以返回XML文档，JSON文档，HTML，Wicket Component ，无论您可以使用哪种形式进行演示，而与 Book 无关

So, it's ok to return an XML document, JSON document, HTML, a Wicket Component, whatever it is you can use for presentation that is independent of the Book.

或者，该方法可以使用一个参数来表示自己 to .像AWT Component.paint(Graphics g)之类的.

Or, the method could take an argument to present itself to. Like AWT Component.paint(Graphics g) or something.

注意:这实际上是一个有争议的主题.混合范式开发(过程和ood的混合)会认为表示需要与对象分离，而面向对象的对象则认为数据和功能始终是同一对象.

Note: this is actually a controversial subject. Mixed-paradigm development (a mix of procedural and ood) would argue that presentation needs to be separated from objects, while object-orientation argues that data and function belong always together.

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