blocks|key|585497|text|对于实现List接口的集合，可以调用listIterator()方法来获取ListIterator。迭代器有两个方法--+nextIndex()，获取索引；next()，获取值(和其他迭代器一样)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|585498|因此，上面的Python的Java等效项可能是：|585499|import+java.util.ListIterator;++
import+java.util.List;

List<String>+numbers+=+Arrays.asList("zero",+"one",+"two");
ListIterator<String>+it+=+numbers.listIterator();
while+(it.hasNext())+{
++++System.out.println(it.nextIndex()+%2B+"+"+%2B+it.next());
}|code-block|syntax|javascript|585500|它和Python一样，输出如下：|585501|0+zero
1+one
2+two|585502|entityMap|0|LINK|mutability|MUTABLE|url|http://download.oracle.com/javase/7/docs/api/java/util/List.html|1|http://download.oracle.com/javase/7/docs/api/java/util/List.html#listIterator%2528%2529|2|http://download.oracle.com/javase/7/docs/api/java/util/ListIterator.html|3|http://download.oracle.com/javase/7/docs/api/java/util/ListIterator.html#nextIndex%2528%2529|4|http://download.oracle.com/javase/7/docs/api/java/util/ListIterator.html#next%2528%2529^0|4|4|I|E|11|C|1P|B|26|6|4|4|0|I|E|1|11|C|2|1P|B|3|26|6|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@$9|1H|A|1I|1|1J]|$9|1K|A|1L|1|1M]|$9|1N|A|1O|1|1P]|$9|1Q|A|1R|1|1S]|$9|1T|A|1U|1|1V]]|E|$]]|$1|F|3|G|5|6|7|1W|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1X|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1Y|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1Z|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|20|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]|10|$5|T|U|V|E|$W|11]]|12|$5|T|U|V|E|$W|13]]|14|$5|T|U|V|E|$W|15]]]]

For collections that implement the <a href="http://download.oracle.com/javase/7/docs/api/java/util/List.html" rel="nofollow noreferrer"><code>List</code></a> interface, you can call the <a href="http://download.oracle.com/javase/7/docs/api/java/util/List.html#listIterator%28%29" rel="nofollow noreferrer"><code>listIterator()</code></a> method to get a <a href="http://download.oracle.com/javase/7/docs/api/java/util/ListIterator.html" rel="nofollow noreferrer"><code>ListIterator</code></a>. The iterator has (amongst others) two methods - <a href="http://download.oracle.com/javase/7/docs/api/java/util/ListIterator.html#nextIndex%28%29" rel="nofollow noreferrer"><code>nextIndex()</code></a>, to get the index; and <a href="http://download.oracle.com/javase/7/docs/api/java/util/ListIterator.html#next%28%29" rel="nofollow noreferrer"><code>next()</code></a>, to get the value (like other iterators).
So a Java equivalent of the Python above might be:
<pre><code>import java.util.ListIterator; 
import java.util.List;

List&lt;String&gt; numbers = Arrays.asList(&quot;zero&quot;, &quot;one&quot;, &quot;two&quot;);
ListIterator&lt;String&gt; it = numbers.listIterator();
while (it.hasNext()) {
 System.out.println(it.nextIndex() + &quot; &quot; + it.next());
}
</code></pre>
which, like the Python, outputs:
<pre><code>0 zero
1 one
2 two
</code></pre>

blocks|key|585578|text|不是的。也许有一些库可以支持这样的功能。但是如果你求助于标准库，你的工作就是计算。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|585579|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|$]]

No. Maybe there are some libraries for supporting such a functionality. But if you resort to the standard libraries it is your job to count.

blocks|key|585591|text|List<String>+list+=+{+"foo",+"bar",+"foobar"};
int+i+=+0;
for+(String+str+:+list){
+++++System.out.println(i%2B%2B+%2B+str+);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|585592|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>List&lt;String&gt; list = { "foo", "bar", "foobar"};
int i = 0;
for (String str : list){
 System.out.println(i++ + str );
}
</code></pre>

blocks|key|585669|text|根据Python文档(here)，这是您能获得的最接近Java的代码，并且不再冗长：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|585670|String[]+numbers+=+{"zero",+"one",+"two"}
for+(int+i+=+0;+i+<+numbers.length;+i%2B%2B)+//+Note+that+length+is+a+property+of+an+array,+not+a+function+(hence+the+lack+of+()+)
++++System.out.println(i+%2B+"+"+%2B+numbers[i]);
}|code-block|syntax|javascript|585671|如果您需要使用List类...|style|CODE|585672|List<String>+numbers+=+Arrays.asList("zero",+"one",+"two");
for+(int+i+=+0;+i+<+numbers.size();+i%2B%2B)+{
++++System.out.println(i+%2B+"+"+%2B+numbers.get(i));
}|585673|*注意:如果在遍历列表时需要修改列表，则需要使用迭代器对象，因为它可以在不引发ConcurrentModificationException的情况下修改列表。|585674|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/2/library/functions.html#enumerate^0|B|4|0|0|0|7|4|0|0|13|V|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@$A|14|B|15|K|L]]|9|@]|C|$]]|$1|M|3|N|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|O|3|P|5|6|7|17|8|@$A|18|B|19|K|L]]|9|@]|C|$]]|$1|Q|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]]]

According to the Python docs (<a href="http://docs.python.org/2/library/functions.html#enumerate" rel="noreferrer">here</a>), this is the closest you can get with Java, and it's no more verbose:

<pre><code>String[] numbers = {"zero", "one", "two"}
for (int i = 0; i &lt; numbers.length; i++) // Note that length is a property of an array, not a function (hence the lack of () )
 System.out.println(i + " " + numbers[i]);
}
</code></pre>

If you need to use the <code>List</code> class...

<pre><code>List&lt;String&gt; numbers = Arrays.asList("zero", "one", "two");
for (int i = 0; i &lt; numbers.size(); i++) {
 System.out.println(i + " " + numbers.get(i));
}
</code></pre>

*NOTE: if you need to modify the list as you're traversing it, you'll need to use the Iterator object, as it has the ability to modify the list without raising a <code>ConcurrentModificationException</code>.

blocks|key|801743|text|我认为这应该是最类似于python“枚举”的java功能，尽管它相当复杂和低效。基本上，只需使用ListIterator或收集器将列表的索引映射到其元素：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|801744|List<String>+list+=+new+LinkedList<>(Arrays.asList("one",+"two",+"three",+"four"));
Map<Integer,+String>+enumeration+=+new+Map<>();
ListIterator+iter+=+list.listIterator();
while(iter.hasNext){
++++map.put(iter.nextIndex(),+iter.next());
}|code-block|syntax|javascript|801745|或者使用lambda表达式：|801746|Set<Integer,+String>+enumeration+=+IntStream.range(0,+list.size()).boxed.collect(Collectors.toMap(index+->+index,+index+->+list.get(index)));|801747|然后，您可以将其与增强的for循环一起使用：|801748|for+(Map.Entry<Integer,+String>+entry+:+enumeration.entrySet){
++++System.out.println(entry.getKey()+%2B+"\t"+%2B+entry.getValue());
}|801749|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

I think this should be the java functionality that resemble the python "enumerate" most, though it is quite complicated and inefficent. Basically, just map the list's indices to its elements, using ListIterator or Collector:

<pre><code>List&lt;String&gt; list = new LinkedList&lt;&gt;(Arrays.asList("one", "two", "three", "four"));
Map&lt;Integer, String&gt; enumeration = new Map&lt;&gt;();
ListIterator iter = list.listIterator();
while(iter.hasNext){
 map.put(iter.nextIndex(), iter.next());
}
</code></pre>

or using lambda expression:

<pre><code>Set&lt;Integer, String&gt; enumeration = IntStream.range(0, list.size()).boxed.collect(Collectors.toMap(index -&gt; index, index -&gt; list.get(index)));
</code></pre>

then you can use it with an enhanced for loop:

<pre><code>for (Map.Entry&lt;Integer, String&gt; entry : enumeration.entrySet){
 System.out.println(entry.getKey() + "\t" + entry.getValue());
}
</code></pre>

blocks|key|801858|text|现在，有了Java8s+Stream+API，再加上提供StreamUtils的小型ProtonPack库，就可以很容易地实现它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|801859|第一个示例使用与问题中相同的for-each符号：|801860|Stream<String>+numbers+=+Arrays.stream("zero+one+two".split("+"));
List<Indexed<String>>+indexedNumbers+=+StreamUtils.zipWithIndex(numbers)
++++++++++++++++++++++++++++++++++++++++++++++++++.collect(Collectors.toList());
for+(Indexed<String>+indexed+:+indexedNumbers)+{
++++System.out.println(indexed.getIndex()+%2B+"+"+%2B+indexed.getValue());
}|code-block|syntax|javascript|801861|虽然上面没有提供Python中的惰性计算。为此，您必须使用forEach()+Stream+API方法：|801862|Stream<String>+numbers+=+Arrays.stream("zero+one+two".split("+"));
StreamUtils.zipWithIndex(numbers)
++++++++.forEach(n+->+System.out.println(n.getIndex()+%2B+"+"+%2B+n.getValue()));|801863|惰性评估可以用以下无限流进行验证：|801864|Stream<Integer>+infStream+=+Stream.iterate(0,+i+->+i%2B%2B);
StreamUtils.zipWithIndex(infStream)
++++++++.limit(196)
++++++++.forEach(n+->+System.out.println(n.getIndex()+%2B+"+"+%2B+n.getValue()));|801865|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/poetix/protonpack^0|S|B|16|A|16|A|0|0|0|0|T|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|F|3|G|5|6|7|1A|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1B|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|1F|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1G|8|@]|D|@]|E|$]]|$1|S|3|T|5|J|7|1H|8|@]|D|@]|E|$K|L]]|$1|U|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]]]

Now with Java 8s Stream API together with the small <a href="https://github.com/poetix/protonpack" rel="nofollow"><code>ProtonPack</code></a> library providing <code>StreamUtils</code> it can be achieved easily.

The first example uses the same for-each notation as in the question:

<pre><code>Stream&lt;String&gt; numbers = Arrays.stream("zero one two".split(" "));
List&lt;Indexed&lt;String&gt;&gt; indexedNumbers = StreamUtils.zipWithIndex(numbers)
 .collect(Collectors.toList());
for (Indexed&lt;String&gt; indexed : indexedNumbers) {
 System.out.println(indexed.getIndex() + " " + indexed.getValue());
}
</code></pre>

Above although does not provide the lazy evaluation as in Python.
For that you must use the <code>forEach()</code> Stream API method:

<pre><code>Stream&lt;String&gt; numbers = Arrays.stream("zero one two".split(" "));
StreamUtils.zipWithIndex(numbers)
 .forEach(n -&gt; System.out.println(n.getIndex() + " " + n.getValue()));
</code></pre>

The lazy evaluation can be verified with the following infinite stream:

<pre><code>Stream&lt;Integer&gt; infStream = Stream.iterate(0, i -&gt; i++);
StreamUtils.zipWithIndex(infStream)
 .limit(196)
 .forEach(n -&gt; System.out.println(n.getIndex() + " " + n.getValue()));
</code></pre>

blocks|key|801942|text|简单明了|type|unstyled|depth|inlineStyleRanges|entityRanges|data|801943|public+static+<T>+void+enumerate(Iterable<T>+iterable,+java.util.function.ObjIntConsumer<T>+consumer)+{
++++int+i+=+0;
++++for(T+object+:+iterable)+{
++++++++consumer.accept(object,+i);
++++++++i%2B%2B;
++++}
}|code-block|syntax|javascript|801944|示例用法：|801945|void+testEnumerate()+{
++++List<String>+strings+=+Arrays.asList("foo",+"bar",+"baz");
++++enumerate(strings,+(str,+i)+->+{
++++++++System.out.println(String.format("Index:%25d+String:%25s",+i,+str));
++++});
}|801946|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Simple and straightforward

<pre><code>public static &lt;T&gt; void enumerate(Iterable&lt;T&gt; iterable, java.util.function.ObjIntConsumer&lt;T&gt; consumer) {
 int i = 0;
 for(T object : iterable) {
 consumer.accept(object, i);
 i++;
 }
}
</code></pre>

Sample usage:

<pre><code>void testEnumerate() {
 List&lt;String&gt; strings = Arrays.asList("foo", "bar", "baz");
 enumerate(strings, (str, i) -&gt; {
 System.out.println(String.format("Index:%d String:%s", i, str));
 });
}
</code></pre>

blocks|key|801979|text|使用Java8+Streams的语法与此基本相同|type|unstyled|depth|inlineStyleRanges|entityRanges|data|801980|++++ArrayList<String>+numbers+=+new+ArrayList<String>();
++++numbers.add("one");
++++numbers.add("two");
++++numbers.add("three");

++++numbers.stream().forEach(num+->
++++{
++++++++System.out.println(numbers.indexOf(num)+%2B+"+"+%2B+num);
++++});|code-block|syntax|javascript|801981|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Pretty much the same syntax using Java8 Streams

<pre><code> ArrayList&lt;String&gt; numbers = new ArrayList&lt;String&gt;();
 numbers.add("one");
 numbers.add("two");
 numbers.add("three");

 numbers.stream().forEach(num -&gt;
 {
 System.out.println(numbers.indexOf(num) + " " + num);
 });
</code></pre>

In Python, the <a href="http://docs.python.org/library/functions.html#enumerate" rel="noreferrer"><code>enumerate</code></a> function allows you to iterate over a sequence of (index, value) pairs. For example:

<pre><code>&gt;&gt;&gt; numbers = ["zero", "one", "two"]
&gt;&gt;&gt; for i, s in enumerate(numbers):
... print i, s
... 
0 zero
1 one
2 two
</code></pre>

Is there any way of doing this in Java?

Is there a Java equivalent of Python's 'enumerate' function?

在Python语言中，函数允许您遍历一系列(索引、值)对。例如：>>> numbers = ["zero", "one", "two"]>>> for i, s in enumerate(numbers):...     print i, s... 0 zero1 one2 two在Java中有什么办法做到这一点吗？

问Java中有没有与Python的“enumerate”函数等效的函数？
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