blocks|key|3356071|text|如果您使用的是Java8，请考虑Optional类，但请注意，它并不适用于所有地方。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3356072|许多人认为(包括我在内)+Optional应该只用于返回值，而不是参数，尤其是不能用于对象属性。然而，像往常一样，没有硬规则，只是要小心，不要盲目地用Optional代替null处理，而不知道你是否从中获得了任何好处。|style|CODE|3356073|例如，在示例代码中，Optional不会给您带来任何好处。由于无论是否为if(s.isPresent())都要执行一些操作，因此只需将if(s+==+null)更改为null即可。但是，如果逻辑只有在s不为空的情况下才执行某些操作，那么在没有else的情况下，您可以使用Optional.ifPresent()来使事情变得更清晰一些。当然，Optional中还有其他有用的方法可以让您获得更干净的代码，比如orElse()，它可以有效地用于使用默认值。|3356074|entityMap|0|LINK|mutability|MUTABLE|url|http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html^0|G|8|0|0|D|8|23|8|0|A|8|10|H|1V|D|3D|4|3R|K|4Q|8|5N|8|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]]|C|$]]|$1|D|3|E|5|6|7|V|8|@$A|W|B|X|F|G]|$A|Y|B|Z|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|10|8|@$A|11|B|12|F|G]|$A|13|B|14|F|G]|$A|15|B|16|F|G]|$A|17|B|18|F|G]|$A|19|B|1A|F|G]|$A|1B|B|1C|F|G]|$A|1D|B|1E|F|G]]|9|@]|C|$]]|$1|J|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]]|K|$L|$5|M|N|O|C|$P|Q]]]]

If you're using Java 8, consider the <a href="http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html" rel="nofollow noreferrer">Optional</a> class, but do note that it's not applicable everywhere.

Many think (me included) that <code>Optional</code> should be used only for return values, not parameters and especially not for object attributes. However as always there's no hard rule, just be careful that you don't replace null handling with <code>Optional</code> blindly, without understanding if you get any advantage from it.

In the example code for example, <code>Optional</code> won't do you any good. Since you perform some action regardless of null or not, you'll just be changing <code>if(s == null)</code> to <code>if(s.isPresent())</code>. However if the logic did something only if s is non-null, without an <code>else</code> you may be able to use <code>Optional.ifPresent()</code> to make things a bit cleaner. Of course there are other useful methods present in <code>Optional</code> that will give you cleaner code, such as the <code>orElse()</code> which can be used effectively for using default values.

blocks|key|2298363|text|您可以抛出NoSuchElementException，这与"fail+fast"的方法很好地结合在一起。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2298364|然而，，如果你的代码开始使用流控制的异常机制-这是一个非常大的禁忌，你应该避免它。|style|BOLD|2298365|一个很好的经验法则是，只有当你的API也支持contains()+(或HasSomeObject(obj))方法时，如果元素不存在，就抛出一个异常。|CODE|2298366|2298367|免责声明:这个答案适用于java-8之前的代码，对于java8，更好的实践可能是可选的，as+suggested+by+@Kayman|2298368|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/util/NoSuchElementException.html|1|http://en.wikipedia.org/wiki/Fail-fast|2|https://stackoverflow.com/a/29918136/572670^0|5|M|0|U|B|1|0|0|3|0|M|A|Z|I|0|0|18|N|2|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]|$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|6|7|16|8|@$A|17|B|18|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|19|8|@$A|1A|B|1B|F|J]|$A|1C|B|1D|F|J]]|9|@]|C|$]]|$1|K|3|-4|5|6|7|1E|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|1F|8|@]|9|@$A|1G|B|1H|1|1I]]|C|$]]|$1|N|3|-4|5|6|7|1J|8|@]|9|@]|C|$]]]|O|$P|$5|Q|R|S|C|$T|U]]|V|$5|Q|R|S|C|$T|W]]|X|$5|Q|R|S|C|$T|Y]]]]

You can throw <a href="http://docs.oracle.com/javase/7/docs/api/java/util/NoSuchElementException.html" rel="nofollow noreferrer">NoSuchElementException</a>, this goes well with the methadology of <a href="http://en.wikipedia.org/wiki/Fail-fast" rel="nofollow noreferrer">"fail fast"</a>.

However, if your code is starting to use the exception mechanism for flow control - this is a very big no-no, and you should avoid it.
 A good rule of thumb is to throw an exception if element does not exist, only if your API also supports <code>contains()</code> (or <code>HasSomeObject(obj)</code>) method.

<hr>

Disclaimer: This answer fits for prior to java-8 code, for java8, a better practice will probably be Optional, <a href="https://stackoverflow.com/a/29918136/572670">as suggested by @Kayman</a>

blocks|key|3356120|text|您可以考虑的一种常见方法是Null+Object+Pattern。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3356121|您返回的不是NULL，而是一个正确对象类型的实例，当您调用它的方法时，它什么也不做。它并不适合所有的情况，但它值得考虑。|3356122|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Null_Object_pattern^0|D|J|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

One common approach that you could consider is the <a href="http://en.wikipedia.org/wiki/Null_Object_pattern" rel="nofollow" title="Null Object Pattern">Null Object Pattern</a>. 

Rather than returning a NULL, you return an instance of the correct object type, that just does nothing when you call its methods. It doesn't fit in all cases, but its worth thinking about.

blocks|key|5467918|text|看起来您指的是special+case模式(特定的实现是Option或Null+Object模式)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|5467919|在Java+8和Guava库中有名为Optional的Option类型的Java实现。|style|CODE|5467920|在您的示例中，您将使用Optional<SomeObject>并拥有此实现(我使用的是Guava实现)：|5467921|Optional<SomeObject>+getSomeObject(List<SomeObject>,+int+x)+{
++++/*+Search+for+object+in+list+that+has+a+properties
++++++++with+value+x+*/
++++if+(found)+{
++++++++return+Optional.of(objectFound);
++++}+else+{
++++++++return+Optional.absent();+//+or+Optional.empty();+in+Java+8
++++}
++++//+if+objectFound+variable+is+null+when+not+found,+you+can+simply+use
++++//+return+Optional.fromNullable(objectFound);
++++//+or+return+Optional.ofNullable(objectFound);+in+Java+8
}|code-block|syntax|javascript|5467922|因此，返回一个可选对象的代码是自解释的。然后，您将拥有：|5467923|void+doSomething(Optional<SomeObject>+o)+{
++++if+(o.isPresent())+{
++++++++SomeObject+someObject+=+o.get();
++++++++/*+Do+action+1+*/
++++}+else+{
++++++++/*+Do+action+2+*/
++++}
++++//+or+opt.map(/*+action+1+*/).orElse(/*+action+2+*/);+in+Java+8
}|5467924|entityMap|0|LINK|mutability|MUTABLE|url|http://martinfowler.com/eaaCatalog/specialCase.html|1|http://en.wikipedia.org/wiki/Option_type|2|http://en.wikipedia.org/wiki/Null_Object_pattern|3|http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html|4|https://code.google.com/p/guava-libraries/wiki/UsingAndAvoidingNullExplained^0|7|C|0|S|6|1|Z|B|2|0|I|8|1|6|3|8|5|4|0|B|K|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@$A|19|B|1A|1|1B]|$A|1C|B|1D|1|1E]|$A|1F|B|1G|1|1H]]|C|$]]|$1|D|3|E|5|6|7|1I|8|@$A|1J|B|1K|F|G]]|9|@$A|1L|B|1M|1|1N]|$A|1O|B|1P|1|1Q]]|C|$]]|$1|H|3|I|5|6|7|1R|8|@$A|1S|B|1T|F|G]]|9|@]|C|$]]|$1|J|3|K|5|L|7|1U|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1V|8|@]|9|@]|C|$]]|$1|Q|3|R|5|L|7|1W|8|@]|9|@]|C|$M|N]]|$1|S|3|-4|5|6|7|1X|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]|10|$5|V|W|X|C|$Y|11]]|12|$5|V|W|X|C|$Y|13]]|14|$5|V|W|X|C|$Y|15]]|16|$5|V|W|X|C|$Y|17]]]]

Looks like you mean the <a href="http://martinfowler.com/eaaCatalog/specialCase.html" rel="nofollow">special case</a> pattern (particular implementations are the <a href="http://en.wikipedia.org/wiki/Option_type" rel="nofollow">Option</a> or the <a href="http://en.wikipedia.org/wiki/Null_Object_pattern" rel="nofollow">Null Object</a> pattern).

There are Java implementations of the Option type, named <code>Optional</code>, in <a href="http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html" rel="nofollow">Java 8</a> and in the <a href="https://code.google.com/p/guava-libraries/wiki/UsingAndAvoidingNullExplained" rel="nofollow">Guava</a> libraries.

In your case, you'll be using <code>Optional&lt;SomeObject&gt;</code> and having this implementation (I'm using the Guava implementation):

<pre><code>Optional&lt;SomeObject&gt; getSomeObject(List&lt;SomeObject&gt;, int x) {
 /* Search for object in list that has a properties
 with value x */
 if (found) {
 return Optional.of(objectFound);
 } else {
 return Optional.absent(); // or Optional.empty(); in Java 8
 }
 // if objectFound variable is null when not found, you can simply use
 // return Optional.fromNullable(objectFound);
 // or return Optional.ofNullable(objectFound); in Java 8
}
</code></pre>

So the code is self-explainable about returning an optional object. You would then have:

<pre><code>void doSomething(Optional&lt;SomeObject&gt; o) {
 if (o.isPresent()) {
 SomeObject someObject = o.get();
 /* Do action 1 */
 } else {
 /* Do action 2 */
 }
 // or opt.map(/* action 1 */).orElse(/* action 2 */); in Java 8
}
</code></pre>

Supposed I have a <code>List&lt;SomeObject&gt;</code> and have a function that return the reference of that object if available.

<pre><code>SomeObject GetSomeObject(List&lt;SomeObject&gt;, int x){
 /* Search for object in list that has a properties
 with value x */

 if (found)
 return /* The object found */
 else
 return NULL;
}

void DoSomething(SomeObject S){
 if(S!=NULL){
 /* Do action 1 */
 }
 else{
 /* Do action 2 */
 }
}
</code></pre>

I've read somewhere that returning <code>NULL</code> is not part of clean code. So I was wondering what is the equivalent code for this case.

UPDATE: I've read <a href="https://stackoverflow.com/questions/271526">this question</a> and I think my case is different. In that case, if <code>NULL</code> is returned then do nothing, while I need to do something if <code>NULL</code> is returned

How to avoid returning NULL value in a function (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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假设我有一个List<SomeObject>，并且有一个函数可以返回该对象引用。SomeObject GetSomeObject(List<SomeObject>, int x){ /* Search for object in list that has a properties with val...

问如何避免在函数(JAVA)中返回空值？
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问如何避免在函数(JAVA)中返回空值？EN