Java的Enum声明的含义是什么？ [英] What is the meaning of the Java's Enum declaration?

问题描述

浏览Java的源代码，我发现了下面的声明：

  public abstract class Enum< E extends Enum< E  - 代替;> 
  

应该如何解释？我坚持使用它...

谢谢。

解决方案

<这就像奎宁！

  public abstract class Foo< E extends Foo< E>> 
 {
 
 public static void use（Foo< E> foo）{
 //使用foo 
} 
} 
  

如果您有以下课程：

  public class FooImpl extends Foo< FooImpl> {b $ b // ... 
} 
  

然后这些递归的魔力模板给你，是这样的：

• Foo 模板要求其参数扩展本身（Foo）。
  
• 如果参数类 E 继而扩展 Foo< E> / code>（它必须因为前一点），那么你已经确保 Foo 模板具有它的子类的感知，因为它的子类是作为模板参数传递给它


• 这又意味着 Foo 的方法可以安全地向下转换这个指向其派生子类 E 的指针。

Surfing on the source code of Java, I found the following declaration:

public abstract class Enum<E extends Enum<E>>

How should it be interpreted? I'm stuck with it...

Thank you.

解决方案

It's like quining! @LES2 is on the right track.

public abstract class Foo <E extends Foo<E>> 
{

   public static void use(Foo<E> foo) {
      // use foo
   }
}

If you have the following class:

public class FooImpl extends Foo<FooImpl> {
  // ...
}

then the magic that these recursive templates gives you, is that:

• the Foo template requires that its parameter extends itself (Foo).
• If the parameter class E, in turn, extends Foo<E> (it has to because of the previous point) then you have ensured that the Foo template has an "awareness" of its subclass, since its subclass is passed into it as a template parameter
• which in turn means that Foo's methods can safely downcast the this pointer to its derived subclass E.

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