blocks|key|2061115|text|不，枚举应该是一个完整的静态枚举。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2061116|在编译时，您可能希望从另一个源文件生成枚举.java文件。您甚至可以像这样创建一个.class文件。|2061117|在某些情况下，您可能需要一组标准值，但允许扩展。通常的做法是为接口提供一个interface，并为标准值提供一个实现该interface的enum。当然，当您只有一个对interface的引用时，您将失去switch的能力。|offset|length|style|CODE|2061118|entityMap^0|0|0|11|9|1N|9|1X|4|2C|9|2U|6|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@$F|O|G|P|H|I]|$F|Q|G|R|H|I]|$F|S|G|T|H|I]|$F|U|G|V|H|I]|$F|W|G|X|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|K|$]]

No, enums are supposed to be a complete static enumeration.

At compile time, you might want to generate your enum .java file from another source file of some sort. You could even create a .class file like this.

In some cases you might want a set of standard values but allow extension. The usual way to do this is have an <code>interface</code> for the interface and an <code>enum</code> that implements that <code>interface</code> for the standard values. Of course, you lose the ability to <code>switch</code> when you only have a reference to the <code>interface</code>.

blocks|key|1847172|text|在幕后，枚举是具有私有构造函数和一堆枚举类型的公共静态终结值(参见here的示例)的POJO。事实上，在Java5之前，以这种方式构建您自己的枚举被认为是最佳实践，Java5引入了enum关键字作为速记。请参阅Enum的源代码以了解更多信息。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1847173|因此，使用构造函数读取或传递给构造函数的公共静态最终常量数组编写您自己的“TypeSafeEnum”应该没有问题。|1847174|另外，帮自己一个忙，覆盖equals、hashCode和toString，如果可能的话，创建一个values方法|1847175|问题是如何使用这种动态枚举...您不能从文件中读取值"PI=3.14“来创建enum+MathConstants，然后继续在您想要的任何地方使用MathConstants.PI……|1847176|entityMap|0|LINK|mutability|MUTABLE|url|http://snipplr.com/view/1655/typesafe-enum-pattern/|1|http://www.docjar.com/html/api/java/lang/Enum.java.html^0|2I|4|X|4|0|2X|4|1|0|0|C|6|J|8|S|8|1C|6|0|12|I|20|G|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@$9|Y|A|Z|1|10]|$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|6|7|14|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]|T|$5|O|P|Q|E|$R|U]]]]

Behind the curtain, enums are POJOs with a private constructor and a bunch of public static final values of the enum's type (see <a href="http://snipplr.com/view/1655/typesafe-enum-pattern/" rel="noreferrer">here</a> for an example). In fact, up until Java5, it was considered best-practice to build your own enumeration this way, and Java5 introduced the <code>enum</code> keyword as a shorthand. See the source for <a href="http://www.docjar.com/html/api/java/lang/Enum.java.html" rel="noreferrer">Enum&lt;T&gt;</a> to learn more.

So it should be no problem to write your own 'TypeSafeEnum' with a public static final array of constants, that are read by the constructor or passed to it.

Also, do yourself a favor and override <code>equals</code>, <code>hashCode</code> and <code>toString</code>, and if possible create a <code>values</code> method

The question is how to use such a dynamic enumeration... you can't read the value "PI=3.14" from a file to create <code>enum MathConstants</code> and then go ahead and use <code>MathConstants.PI</code> wherever you want...

blocks|key|1847273|text|您可以在运行时从源代码加载Java类。(使用JCI、BeanShell或JavaCompiler)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1847274|这将允许您随心所欲地更改枚举值。|1847275|注意:这不会改变引用这些枚举的任何类，因此这在现实中可能不是很有用。|1847276|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

You can load a Java class from source at runtime. (Using JCI, BeanShell or JavaCompiler)

This would allow you to change the Enum values as you wish.

Note: this wouldn't change any classes which referred to these enums so this might not be very useful in reality.

blocks|key|1847358|text|您可以尝试将属性分配给您正在尝试创建的ENUM，并通过使用加载的属性文件静态地构造它。这是一个很大的技巧，但它是有效的:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1847359|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You could try to assign properties to the ENUM you're trying to create and statically contruct it by using a loaded properties file. Big hack, but it works :)

blocks|key|1847396|text|我在formative+project+of+my+young+career上遇到了这个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1847397|我采用的方法是将枚举的值和名称保存在外部，最终目标是能够编写看起来尽可能接近语言枚举的代码。|1847398|我希望我的解决方案是这样的：|1847399|enum+HatType
{
++++BASEBALL,
++++BRIMLESS,
++++INDIANA_JONES
}

HatType+mine+=+HatType.BASEBALL;

//+prints+"BASEBALL"
System.out.println(mine.toString());

//+prints+true
System.out.println(mine.equals(HatType.BASEBALL));|code-block|syntax|javascript|1847400|我最终得到了这样的结果：|1847401|//+in+a+file+somewhere:
//+1+-->+BASEBALL
//+2+-->+BRIMLESS
//+3+-->+INDIANA_JONES

HatDynamicEnum+hats+=+HatEnumRepository.retrieve();

HatEnumValue+mine+=+hats.valueOf("BASEBALL");

//+prints+"BASEBALL"
System.out.println(mine.toString());

//+prints+true
System.out.println(mine.equals(hats.valueOf("BASEBALL"));|1847402|由于我的要求是必须能够在运行时将成员添加到枚举，因此我也实现了该功能：|1847403|hats.addEnum("BATTING_PRACTICE");

HatEnumRepository.storeEnum(hats);

hats+=+HatEnumRepository.retrieve();

HatEnumValue+justArrived+=+hats.valueOf("BATTING_PRACTICE");
//+file+now+reads:
//+1+-->+BASEBALL
//+2+-->+BRIMLESS
//+3+-->+INDIANA_JONES
//+4+-->+BATTING_PRACTICE|1847404|我将其命名为动态枚举“模式”，您可以阅读有关the+original+design和its+revised+edition的文章。|1847405|两者之间的不同之处在于，修订版是在我真正开始摸索OO和DDD之后设计的。当我还在编写名义上的过程性DDD时，在时间压力下我设计了第一个。|1847406|entityMap|0|LINK|mutability|MUTABLE|url|http://moffdub.wordpress.com/2008/04/28/introducing-the-project/|1|http://moffdub.wordpress.com/2008/05/09/dynamic-enumerations/|2|http://moffdub.wordpress.com/2009/01/14/dynamic-enumerations-revisited/^0|2|10|0|0|0|0|0|0|0|0|0|M|J|1|16|J|2|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@$A|1B|B|1C|1|1D]]|C|$]]|$1|D|3|E|5|6|7|1E|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|1F|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|1G|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|1H|8|@]|9|@]|C|$]]|$1|O|3|P|5|J|7|1I|8|@]|9|@]|C|$K|L]]|$1|Q|3|R|5|6|7|1J|8|@]|9|@]|C|$]]|$1|S|3|T|5|J|7|1K|8|@]|9|@]|C|$K|L]]|$1|U|3|V|5|6|7|1L|8|@]|9|@$A|1M|B|1N|1|1O]|$A|1P|B|1Q|1|1R]]|C|$]]|$1|W|3|X|5|6|7|1S|8|@]|9|@]|C|$]]|$1|Y|3|-4|5|6|7|1T|8|@]|9|@]|C|$]]]|Z|$10|$5|11|12|13|C|$14|15]]|16|$5|11|12|13|C|$14|17]]|18|$5|11|12|13|C|$14|19]]]]

I faced this problem on the <a href="http://moffdub.wordpress.com/2008/04/28/introducing-the-project/" rel="noreferrer">formative project of my young career</a>. 

The approach I took was to save the values and the names of the enumeration externally, and the end goal was to be able to write code that looked as close to a language enum as possible.

I wanted my solution to look like this:

<pre><code>enum HatType
{
 BASEBALL,
 BRIMLESS,
 INDIANA_JONES
}

HatType mine = HatType.BASEBALL;

// prints "BASEBALL"
System.out.println(mine.toString());

// prints true
System.out.println(mine.equals(HatType.BASEBALL));
</code></pre>

And I ended up with something like this:

<pre><code>// in a file somewhere:
// 1 --&gt; BASEBALL
// 2 --&gt; BRIMLESS
// 3 --&gt; INDIANA_JONES

HatDynamicEnum hats = HatEnumRepository.retrieve();

HatEnumValue mine = hats.valueOf("BASEBALL");

// prints "BASEBALL"
System.out.println(mine.toString());

// prints true
System.out.println(mine.equals(hats.valueOf("BASEBALL"));
</code></pre>

Since my requirements were that it had to be possible to add members to the enum at run-time, I also implemented that functionality:

<pre><code>hats.addEnum("BATTING_PRACTICE");

HatEnumRepository.storeEnum(hats);

hats = HatEnumRepository.retrieve();

HatEnumValue justArrived = hats.valueOf("BATTING_PRACTICE");
// file now reads:
// 1 --&gt; BASEBALL
// 2 --&gt; BRIMLESS
// 3 --&gt; INDIANA_JONES
// 4 --&gt; BATTING_PRACTICE
</code></pre>

I dubbed it the Dynamic Enumeration "pattern", and you read about <a href="http://moffdub.wordpress.com/2008/05/09/dynamic-enumerations/" rel="noreferrer">the original design</a> and <a href="http://moffdub.wordpress.com/2009/01/14/dynamic-enumerations-revisited/" rel="noreferrer">its revised edition</a>. 

The difference between the two is that the revised edition was designed after I really started to grok OO and DDD. The first one I designed when I was still writing nominally procedural DDD, under time pressure no less.

It is possible to add and remove elements from an enum in Java at runtime?

For example, could I read in the labels and constructor arguments of an enum from a file?

<hr>

@saua, it's just a question of whether it can be done out of interest really. I was hoping there'd be some neat way of altering the running bytecode, maybe using <a href="http://bcel.sourceforge.net/" rel="noreferrer">BCEL</a> or something. I've also followed up with <a href="https://stackoverflow.com/questions/481068/when-to-use-enum-or-collection-in-java">this question</a> because I realised I wasn't totally sure when an enum should be used.

I'm pretty convinced that the right answer would be to use a collection that ensured uniqueness instead of an enum if I want to be able to alter the contents safely at runtime.

Can I add and remove elements of enumeration at runtime in Java

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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是否可以在运行时在Java中的枚举中添加和删除元素？例如，我可以从文件中读取枚举的标签和构造函数参数吗？@saua，这只是一个问题，它是否真的出于兴趣而这样做。我希望有一些巧妙的方法来改变正在运行的字节码，也许是使用或其他什么。我也跟进了，因为我意识到我不能完全确定什么时候应该使用枚举。我非常确信，如果我想在运行时安全...

问我可以在Java中添加和删除运行时枚举的元素吗
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