blocks|key|1241916|text|我不确定我是否理解了您的意思，但是您似乎相信在前面的代码示例中，throw是switch语法的一部分。事实并非如此。switch块和throw语句是两个独立的东西，在这段代码中，它们恰好放在一起。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1241917|更详细地说：switch中的四个case部件都包含return语句，导致该方法中的任何后续指令都被跳过。如果没有匹配的case部件，则在switch块之后的行上继续执行，该块恰好是一个throw。|1241918|您可以以非常类似的方式在if之后使用throw：|1241919|if+(something)+{
++++return+aValue;
}

throw+new+Exception("Nope");|code-block|syntax|javascript|1241920|entityMap^0|W|5|12|6|1M|6|1U|5|0|6|6|G|4|P|6|1N|4|1W|6|2K|5|0|C|2|I|5|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1H|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|P|$]]

I am not sure if I get you, but you seem to believe that the <code>throw</code> is part of the <code>switch</code> syntax in the posted code sample. That is not the case. The <code>switch</code> block and the <code>throw</code> statement are two seperate things, which just happens to be placed next to each other in this code.

In more detail: The four <code>case</code> parts in the <code>switch</code> all contain <code>return</code> statements, causing any subsequent instructions in the method to be skipped. If none of the <code>case</code> parts matches, execution continues on the line following the <code>switch</code> block, which happens to be a <code>throw</code>.

You could use a <code>throw</code> after an <code>if</code> in a very similar way:

<pre><code>if (something) {
 return aValue;
}

throw new Exception("Nope");
</code></pre>

blocks|key|3360095|text|本教程的作者为抛出AssertionError而感到羞愧--为什么不利用Java语言已经提供的异常，比如UnsupportedOperationException|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3360096|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/j2se/1.5.0/docs/api/java/lang/UnsupportedOperationException.html^0|1G|T|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Shame on the writer of that tutorial for throwing an AssertionError - why not make use of the Exceptions that Java provides us already, like <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/UnsupportedOperationException.html" rel="nofollow noreferrer">UnsupportedOperationException</a>

blocks|key|3359992|text|有一个default关键字：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3359993|switch+(whatever)+{
++//+...
++default:+explode();
}|code-block|syntax|javascript|3359994|如果希望缺省情况抛出异常，则|3359995|++default:+throw+new+Explode();|3359996|您的示例只能按照它的方式工作，因为所有其他分支都是从包含的函数返回的。在我看来，这不是一个很好的编码习惯。|3359997|entityMap^0|3|7|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|Y|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

There's a <code>default</code> keyword:

<pre><code>switch (whatever) {
 // ...
 default: explode();
}
</code></pre>

If you want the default case to throw an exception, then

<pre><code> default: throw new Explode();
</code></pre>

Your example only works the way it does because all the other branches return from the containing function. In my opinion that's not a very good coding habit to get into.

blocks|key|3360021|text|在eclipse中，如果没有在switch语句中包含所有枚举值，则会在编译时生成警告。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3360022|但是，如果设置为default:情况，则该警告将不再有效。所以，是的，在某些IDE中，当所有枚举值都包含在switch语句中时，省略default的情况有一个明显的优势。|offset|length|style|CODE|3360023|一般来说，如果您的switch语句超过5-6种情况，请考虑重新设计代码。通常，人们不会意识到Java中的枚举是成熟的类，枚举值是一级对象，因此在许多情况下，您可以让枚举对象自己完成工作，而不是通过switch语句来驱动行为。|3360024|在此特定示例中，枚举可以具有方法doOp(+int+x,+int+y)，并且每个枚举成员都可以实现该方法的一种特定风格。|3360025|entityMap^0|0|8|8|1U|7|0|0|G|J|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@$D|P|E|Q|F|G]|$D|R|E|S|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|T|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|U|8|@$D|V|E|W|F|G]]|9|@]|A|$]]|$1|L|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|M|$]]

In eclipse, if you do not cover all enum values in a switch statement it generates a warning at compile time.

If, however, you put a <code>default:</code> case that warning does not work anymore. So, yes in some IDEs there is a definite advantage of omitting <code>default</code> case when all enum values are covered in a switch statement.

In general, if your switch statement grows beyond 5-6 cases, consider redesigning the code. Usually, people do not appreciate that enums in Java are full blown classes and enum values are first-class objects, so instead of driving the behavior through the switch statement in many cases you can ask the enum object to do the work itself.

In this particular example the enum can have a method <code>doOp( int x, int y)</code> and each enum member can implement a particular flavor of this method.

blocks|key|3360053|text|正如其他人所说，这不是语法糖。它之所以有效，是因为交换机上的所有分支都是从该方法返回的。如果将某个其他枚举值放入switch中，那么switch语句将在不运行任何分支的情况下完成，之后throw语句将执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3360054|switch(this)+{
++case+PLUS:+++return+x+%2B+y;
++case+MINUS:++return+x+-+y;
++case+TIMES:++return+x+*+y;
++case+DIVIDE:+return+x+/+y;
++default:+throw+new+AssertionError("Unknown+op:+"+%2B+this);
}|code-block|syntax|javascript|3360055|这些代码在功能上是等价的。两者之间的主要区别在于，如果将值添加到Enum而不是switch语句，则不带default子句的switch将创建一个编译器警告。|3360056|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

As others have stated, this is not syntax sugar. It works because all of the branches on the switch return from the method. If some other enum value was put into the switch, the switch statement would complete without running any of the branches, after which the throw statement would execute.

<pre><code>switch(this) {
 case PLUS: return x + y;
 case MINUS: return x - y;
 case TIMES: return x * y;
 case DIVIDE: return x / y;
 default: throw new AssertionError("Unknown op: " + this);
}
</code></pre>

That code would be functionally equivalent. The major difference between the two is that your switch with no default clause will create a compiler warning if a value is added to the Enum but not to the switch statement.

I noticed the following in the Java Language spec in the section on enumerations here: <a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/enums.html" rel="nofollow noreferrer">link</a>

<pre><code>switch(this) {
 case PLUS: return x + y;
 case MINUS: return x - y;
 case TIMES: return x * y;
 case DIVIDE: return x / y;
}
throw new AssertionError("Unknown op: " + this);
</code></pre>

However, looking at the switch statement definition section, I didn't notice this particular syntax (the associated throw statement) anywhere. 

Can I use this sort of "default case is throw an exception" syntactic sugar outside of enum definitions? Does it have any special name? Is this considered a good/bad practice for short-cutting this behavior of "anything not in the list throws an exception"?

Enums With Default Throw Clause?

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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在这里关于枚举的部分中，我注意到Java语言规范中的以下内容：switch(this) {  case PLUS:   return x + y;  case MINUS:  return x - y;  case TIMES:  return x * y;  case DIVIDE: return x / y;}throw new AssertionError("Unknown op: " + 

问使用默认抛出子句的枚举？
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