你如何使用泛型类型作为返回值和泛型类型作为参数？ [英] How do you use a generic type as return value and a generic type as a parameter?

问题描述

我尝试用泛型创建一个抽象类。业务逻辑是将文本从一种语言翻译成另一种语言。每种语言必须有 Translator 类。我还需要每种语言的 LanguageTranslation 类，它是 translate 方法的返回对象，参数 T 。该T应该是 OriginalText 的子类（例如EnglishText，ChineseText等）。这就是我奋斗的地方。你如何编写这个约束？

我已经创建了下面的超类。

  public abstract class Translator< T，V> {
 public abstract< V extends LanguageTranslation> V translate（T originalText）; 
} 
  

如果我误解了泛型的概念或者错误地使用它，请照亮。

解决方案

只需将其添加到您定义泛型的地方即可：

  public abstract class Translator< T extends OriginalText，V> {
 public abstract< V extends LanguageTranslation> V translate（T originalText）; 
 
 
 
 
 
 顺便说一句，这很混乱，因为 V 定义在您的方法中被覆盖。为什么不这样做：
  public abstract class Translator< T extends OriginalText，V extends LanguageTranslation> {
 public abstract V translate（T originalText）; 
 
  
 编辑：解释为什么你对V有一个警告 
 
 
 
完全相同： 
 
 
  public abstract class Translator < T扩展OriginalText，V> {
 public abstract< K extends LanguageTranslation> K translate（T originalText）; 
} 
  
现在在这个方法里面有3个泛型：
 
 
 
 
运行时确定的LanguageTranslation的子类型的K  
 
运行时确定的OriginalText子类型的T  
 
 V运行时确定的对象的子类型（默认约束） 
 
 
I try to create an abstract class with generics. The business logic is to translate a text from one language to another. There must be a Translator class for each language. I also require a LanguageTranslation class for each language, which is the return object of the translate method, which takes on the parameter T. That T is supposed to be of a sub class of OriginalText (e.g. EnglishText, ChineseText, etc). And that is where I struggle. How do you code this constraint?

I've created the following super class.
public abstract class Translator <T, V> {            
    public abstract <V extends LanguageTranslation> V translate(T originalText);
}
If I misunderstand the concept of generics or apply it wrong, please illuminate. Thanks.
解决方案
Just add it where you define your Generics :
public abstract class Translator <T extends OriginalText, V> {            
    public abstract <V extends LanguageTranslation> V translate(T originalText);
}
Btw, this is confusing because the V definition is overriden in your method. Why not doing this :
public abstract class Translator <T extends OriginalText, V extends LanguageTranslation> {            
    public abstract V translate(T originalText);
}
EDIT: explaining why you have a warning on V

It's exactly the same as :
public abstract class Translator <T extends OriginalText, V> {            
    public abstract <K extends LanguageTranslation> K translate(T originalText);
}
Now inside the method you have 3 generics : 


K of runtime determined subtype of LanguageTranslation
T of runtime determined subtype of OriginalText
V runtime determined subtype of Object (default constraint)


                        
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