blocks|key|1269429|text|您指定的两个循环中的第一个是典型的C+for循环。这为程序员提供了对迭代准则的控制，并允许三种操作:初始化；循环测试；增量表达式。虽然它经常用于递增重复一定次数的尝试，如您的示例：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1269430|for+(int+i=0;+i+<+N+:+i%2B%2B)|code-block|syntax|javascript|1269431|在代码中，还有更多使用for迭代集合的实例：|1269432|for+(Iterator+iter+=+myList.iterator();+iter.hasNext();)|1269433|为了证明第二种类型的样例(第三个子句通常未使用)，以及对Java1.5中引入的Generics的补充，引入了两个示例中的第二个-增强的for循环，即for-each+loop。|1269434|第二个用于数组和泛型集合。See+this+documentation。它允许您迭代泛型集合，其中您知道Collection的类型，而不必将Iterator.next()的结果强制转换为已知类型。|1269435|比较：|1269436|for(Iterator+iter+=+myList.iterator;+iter.hasNext()+;+)+{
+++String+myStr+=+(String)+iter.next();
+++//...do+something+with+myStr
}|1269437|使用|1269438|for+(String+myStr+:+myList)+{
+++//...do+something+with+myStr
+}|1269439|这种“新风格”的for循环也可以与数组一起使用：|1269440|String[]+strArray=+...
for+(String+myStr+:+strArray)+{
+++//...do+something+with+myStr
}|1269441|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf|1|http://java.sun.com/j2se/1.5.0/docs/guide/language/foreach.html|2|http://java.sun.com/developer/JDCTechTips/2005/tt0505.html#2^0|J|3|0|0|B|3|0|0|22|D|13|8|0|22|D|1|0|1G|A|1Y|F|D|M|2|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1J|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1K|8|@$9|1L|A|1M|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|1N|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1O|8|@$9|1P|A|1Q|B|C]]|D|@$9|1R|A|1S|1|1T]|$9|1U|A|1V|1|1W]]|E|$]]|$1|Q|3|R|5|6|7|1X|8|@$9|1Y|A|1Z|B|C]|$9|20|A|21|B|C]]|D|@$9|22|A|23|1|24]]|E|$]]|$1|S|3|T|5|6|7|25|8|@]|D|@]|E|$]]|$1|U|3|V|5|H|7|26|8|@]|D|@]|E|$I|J]]|$1|W|3|X|5|6|7|27|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|H|7|28|8|@]|D|@]|E|$I|J]]|$1|10|3|11|5|6|7|29|8|@]|D|@]|E|$]]|$1|12|3|13|5|H|7|2A|8|@]|D|@]|E|$I|J]]|$1|14|3|-4|5|6|7|2B|8|@]|D|@]|E|$]]]|15|$16|$5|17|18|19|E|$1A|1B]]|1C|$5|17|18|19|E|$1A|1D]]|1E|$5|17|18|19|E|$1A|1F]]]]

The first of the two you specify is a classic C <code>for</code> loop. This gives the programmer control over the iteration criteria and allows for three operations: the initialization; the loop test ; the increment expression. Though it is used often to incrementally repeat for a set number of attempts, as in yor example:

<pre><code>for (int i=0; i &lt; N : i++)
</code></pre>

There are many more instances in code where the <code>for</code> was use to iterate over collections: 

<pre><code>for (Iterator iter = myList.iterator(); iter.hasNext();)
</code></pre>

To aleviate the boilerplating of the second type (where the third clause was often unused), and to compliment the <a href="http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf" rel="noreferrer">Generics</a> introduced in Java 1.5, the second of your two examples - the enhanced for loop, or the <a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/foreach.html" rel="noreferrer"><code>for-each loop</code></a> - was introduced. 

The second is used with arrays and Generic collections. <a href="http://java.sun.com/developer/JDCTechTips/2005/tt0505.html#2" rel="noreferrer">See this documentation</a>. It allows you to iterate over a generic collection, where you know the type of the <code>Collection</code>, without having to cast the result of the <code>Iterator.next()</code> to a known type.

Compare:

<pre><code>for(Iterator iter = myList.iterator; iter.hasNext() ; ) {
 String myStr = (String) iter.next();
 //...do something with myStr
}
</code></pre>

with 

<pre><code>for (String myStr : myList) {
 //...do something with myStr
 }
</code></pre>

This 'new style' for loop can be used with arrays as well:

<pre><code>String[] strArray= ...
for (String myStr : strArray) {
 //...do something with myStr
}
</code></pre>

blocks|key|1484053|text|它用于遍历整个数组或Iterable集合。它基本上取代了：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1484054|for(int+i=0;+i<N.length;+i%2B%2B)|code-block|syntax|javascript|1484055|并且可以与泛型一起使用，这非常酷。|1484056|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|$]]

It's used to iterate through an entire array or Iterable collection. It basically replaces:

<pre><code>for(int i=0; i&lt;N.length; i++)
</code></pre>

And can be used with Generics which is quite cool

blocks|key|1484107|text|"for+in“循环主要是让人眼花缭乱的，它使代码更容易阅读。(如果您将:读作"in")。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1484108|当我迭代列表或数组时，我几乎只在自己的代码中使用第二种类型。|1484109|在处理大多数数学代码时，或者当我需要一个"i“来查看我已经循环了多少次时，我仍然使用常规的for循环。|1484110|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|$]]

The "for in" loop is mostly eye-candy that makes code easier to read. (If you pronounce the : as "in").

I use the second type almost exclusively in my own code whenever I'm iterating over a list or array.

I still use the regular for loop when dealing with mostly mathematical code, or when I need an "i" to see how many times I've looped.

blocks|key|1269558|text|它被称为for+each循环，基本上，它可以与任何实现|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1269559|java.lang.Iterable|code-block|syntax|javascript|1269560|泛型集合实现此接口，但您也可以创建自己的类。它使得处理列表/集合中的所有内容变得非常容易，尽管缺点是您不能像在传统循环中那样显式地访问列表中的当前数字。由于对迭代器类的调用，这种类型的循环与传统循环相比存在一些额外的开销。|1269561|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|$]]

It's called a for each loop and basically, it can be used with anything that implements 

<pre><code>java.lang.Iterable
</code></pre>

Generic collections implement this interface, but you could make your own class that did as well. It makes dealing with everything in a list/collection very easy although the downside is that you don't get explicit access to the current number in the list like you do in the traditional loop. There is some additional overhead associated with this type of loop over traditional loops because of the calls to the iterator classes.

I am fairly new to Java and in another Stack Overflow question about <a href="https://stackoverflow.com/questions/1241946/how-is-a-for-loop-structured-in-java">for loops</a> an answer said that there was two uses of for in Java:

<pre><code>for (int i = 0; i &lt; N; i++) {
}


for (String a : anyIterable) {
}
</code></pre>

I know the first use of for and have used it a lot, but I have never seen the second one. What is it used to do and when would I use it?

Uses of 'for' 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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我对Java还很陌生，在另一个关于的堆栈溢出问题中，有一个答案说在Java中有两个for的用法：for (int i = 0; i < N; i++) {}for (String a : anyIterable) {}我知道for的第一个用法，并且用得很多，但我从来没有见过第二个用法。它是用来做什么的，我什么时候使用它...

问“for”在Java中的用法
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