blocks|key|1475902|text|总是追加可能会更容易。然后，当您完成循环时，只需删除最后一个字符。这样的话条件句也会少很多。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1475903|您可以使用索引为length()+-+1的StringBuilder的deleteCharAt(int+index)|offset|length|style|CODE|1475904|entityMap^0|0|8|C|L|D|Z|N|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]|$D|N|E|O|F|G]|$D|P|E|Q|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|I|$]]

It might be easier to always append. And then, when you're done with your loop, just remove the final character. Tons less conditionals that way too.

You can use <code>StringBuilder</code>'s <code>deleteCharAt(int index)</code> with index being <code>length() - 1</code>

blocks|key|1475950|text|如果你把它转换成一个经典的索引循环，是的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1475951|或者，您可以在完成后删除最后一个逗号。如下所示：|1475952|int[]+array+=+{1,+2,+3...};
StringBuilder

builder+=+new+StringBuilder();

for(int+i+:+array)
{
++++builder.append(i+%2B+",");
}

if(builder.charAt((builder.length()+-+1)+==+','))
++++builder.deleteCharAt(builder.length()+-+1);|code-block|syntax|javascript|1475953|我，我只是使用commons-lang的StringUtils.join()。|offset|length|style|CODE|1475954|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/lang/|1|http://commons.apache.org/lang/api-release/org/apache/commons/lang/StringUtils.html#join(java.util.Collection,%2520char)^0|0|0|0|K|I|7|C|0|K|I|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|11|8|@$K|12|L|13|M|N]]|9|@$K|14|L|15|1|16]|$K|17|L|18|1|19]]|A|$]]|$1|O|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]|W|$5|R|S|T|A|$U|X]]]]

If you convert it to a classic index loop, yes.

Or you could just delete the last comma after it's done. Like so:

<pre><code>int[] array = {1, 2, 3...};
StringBuilder

builder = new StringBuilder();

for(int i : array)
{
 builder.append(i + ",");
}

if(builder.charAt((builder.length() - 1) == ','))
 builder.deleteCharAt(builder.length() - 1);
</code></pre>

Me, I just use <a href="http://commons.apache.org/lang/api-release/org/apache/commons/lang/StringUtils.html#join(java.util.Collection,%20char)" rel="nofollow noreferrer"><code>StringUtils.join()</code></a> from <a href="http://commons.apache.org/lang/" rel="nofollow noreferrer">commons-lang</a>.

blocks|key|1691098|text|保持简单，并使用标准for循环：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1691099|for(int+i+=+0+;+i+<+array.length+;+i+%2B%2B+){
++++builder.append(array[i]);
++++if(+i+!=+array.length+-+1+){
++++++++builder.append(',');
++++}
}|code-block|syntax|javascript|1691100|或者只使用apache+commons-lang+StringUtils.join()。|offset|length|1691101|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/lang/api-release/org/apache/commons/lang/StringUtils.html#join(java.lang.Object[],%2520char)^0|0|0|C|V|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

keep it simple and use a standard for loop:

<pre><code>for(int i = 0 ; i &lt; array.length ; i ++ ){
 builder.append(array[i]);
 if( i != array.length - 1 ){
 builder.append(',');
 }
}
</code></pre>

or just use apache <a href="http://commons.apache.org/lang/api-release/org/apache/commons/lang/StringUtils.html#join(java.lang.Object[],%20char)" rel="nofollow noreferrer">commons-lang StringUtils.join()</a>

blocks|key|1476088|text|显式循环总是比隐式循环工作得更好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1476089|builder.append(+""+%2B+array[0]+);
for(+int+i+=+1;+i+!=+array.length;+i+%2B=+1+)+{
+++builder.append(+",+"+%2B+array[i]+);
}|code-block|syntax|javascript|1476090|您应该将整个过程封装在if语句中，以防您处理的是长度为零的数组。|1476091|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|$]]

Explicit loops always work better than implicit ones.

<pre><code>builder.append( "" + array[0] );
for( int i = 1; i != array.length; i += 1 ) {
 builder.append( ", " + array[i] );
}
</code></pre>

You should wrap the whole thing in an if-statement just in case you're dealing with a zero-length array.

blocks|key|1476157|text|另一种方法是将数组的长度(如果可用)存储在单独的变量中(比每次重新检查长度更有效)。然后，您可以将索引与该长度进行比较，以确定是否添加最后一个逗号。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1476158|编辑:另一个注意事项是权衡删除最后一个字符(这可能导致字符串复制)与在每次迭代中检查条件的性能成本。|1476159|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Another approach is to have the length of the array (if available) stored in a separate variable (more efficient than re-checking the length each time). You can then compare your index to that length to determine whether or not to add the final comma.

EDIT: Another consideration is weighing the performance cost of removing a final character (which may cause a string copy) against having a conditional be checked in each iteration.

blocks|key|1691286|text|这里有一个解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1691287|int[]+array+=+{1,+2,+3...};
StringBuilder+builder+=+new+StringBuilder();
bool+firstiteration=true;

for(int+i+:+array)
{
++++if(!firstiteration)
++++++++builder.append(",");

++++builder.append(""+%2B+i);
++++firstiteration=false;
}|code-block|syntax|javascript|1691288|查找第一次迭代:)|1691289|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|$]]

Here is a solution:

<pre><code>int[] array = {1, 2, 3...};
StringBuilder builder = new StringBuilder();
bool firstiteration=true;

for(int i : array)
{
 if(!firstiteration)
 builder.append(",");

 builder.append("" + i);
 firstiteration=false;
}
</code></pre>

Look for the first iteration :)
&nbsp;

blocks|key|1691373|text|这里有两个备用路径：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1691374|1：Apache+Commons+String+Utils|offset|length|1691375|2:保留一个名为first的布尔值，设置为true。在每次迭代中，如果first为false，则附加逗号；之后，将first设置为false。|style|CODE|1691376|entityMap|0|LINK|mutability|MUTABLE|url|https://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/StringUtils.html#join(java.lang.Object[],%2520char)^0|0|2|R|0|0|8|5|Z|5|1L|5|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@$D|T|E|U|1|V]]|A|$]]|$1|F|3|G|5|6|7|W|8|@$D|X|E|Y|H|I]|$D|Z|E|10|H|I]|$D|11|E|12|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]]]

Two alternate paths here:

1: <a href="https://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/StringUtils.html#join(java.lang.Object[],%20char)" rel="nofollow noreferrer">Apache Commons String Utils</a>

2: Keep a boolean called <code>first</code>, set to true. In each iteration, if <code>first</code> is false, append your comma; after that, set <code>first</code> to false.

blocks|key|1476342|text|也许你在工作中使用了错误的工具。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1476343|这比你正在做的更手动，但在某种程度上更优雅，如果不是有点“老派”的话。|1476344|+StringBuffer+buffer+=+new+StringBuffer();
+Iterator+iter+=+s.iterator();
+while+(iter.hasNext())+{
++++++buffer.append(iter.next());
++++++if+(iter.hasNext())+{
++++++++++++buffer.append(delimiter);
++++++}
+}|code-block|syntax|javascript|1476345|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Maybe you are using the wrong tool for the Job.

This is more manual than what you are doing but it's in a way more elegant if not a bit "old school"

<pre><code> StringBuffer buffer = new StringBuffer();
 Iterator iter = s.iterator();
 while (iter.hasNext()) {
 buffer.append(iter.next());
 if (iter.hasNext()) {
 buffer.append(delimiter);
 }
 }
</code></pre>

blocks|key|1476383|text|另一种解决方案(可能是最有效的)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1476384|++++int[]+array+=+{1,+2,+3};
++++StringBuilder+builder+=+new+StringBuilder();

++++if+(array.length+!=+0)+{
++++++++builder.append(array[0]);
++++++++for+(int+i+=+1;+i+<+array.length;+i%2B%2B+)
++++++++{
++++++++++++builder.append(",");
++++++++++++builder.append(array[i]);
++++++++}
++++}|code-block|syntax|javascript|1476385|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|$]]

Another solution (perhaps the most efficient)

<pre><code> int[] array = {1, 2, 3};
 StringBuilder builder = new StringBuilder();

 if (array.length != 0) {
 builder.append(array[0]);
 for (int i = 1; i &lt; array.length; i++ )
 {
 builder.append(",");
 builder.append(array[i]);
 }
 }
</code></pre>

blocks|key|1691523|text|另一种方法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1691524|String+delim+=+"";
for+(int+i+:+ints)+{
++++sb.append(delim).append(i);
++++delim+=+",";
}|code-block|syntax|javascript|1691525|更新:对于Java8，现在有了Collectors|offset|length|1691526|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html^0|0|0|F|A|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

Another way to do this:

<pre><code>String delim = "";
for (int i : ints) {
 sb.append(delim).append(i);
 delim = ",";
}
</code></pre>

Update: For Java 8, you now have <a href="http://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html" rel="noreferrer">Collectors</a>

blocks|key|1476480|text|如果您只是将数组转换为逗号分隔的数组，许多语言都有一个连接函数来实现这一点。它将数组转换为每个元素之间带有分隔符的字符串。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1476481|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|$]]

If you're only turning an array into a comma delimited array, many languages have a join function for exactly this. It turns an array into a string with a delimiter between each element.

blocks|key|1476554|text|你需要Class+Separator。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1476555|Separator+s+=+new+Separator(",+");
for(int+i+:+array)
{
+++++builder.append(s).append(i);
}|code-block|syntax|javascript|1476556|类Separator的实现很简单。它包装了一个字符串，每次调用toString()时都会返回该字符串，但第一次调用除外，因为第一次调用返回一个空字符串。|style|CODE|1476557|entityMap|0|LINK|mutability|MUTABLE|url|http://ssdl-wiki.cs.technion.ac.il/wiki/index.php/Class_Separator^0|3|F|0|0|0|1|9|V|A|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@$A|10|B|11|K|L]|$A|12|B|13|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

You need <a href="http://ssdl-wiki.cs.technion.ac.il/wiki/index.php/Class_Separator" rel="nofollow noreferrer">Class Separator</a>.

<pre><code>Separator s = new Separator(", ");
for(int i : array)
{
 builder.append(s).append(i);
}
</code></pre>

The implementation of class <code>Separator</code> is straight forward. It wraps a string that is returned on every call of <code>toString()</code> except for the first call, which returns an empty string.

blocks|key|1691787|text|基于java.util.AbstractCollection.toString()，它提前退出以避开分隔符。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1691788|StringBuffer+buffer+=+new+StringBuffer();
Iterator+iter+=+s.iterator();
for+(;;)+{
++buffer.append(iter.next());
++if+(!+iter.hasNext())
++++break;
++buffer.append(delimiter);
}|code-block|syntax|javascript|1691789|它是高效和优雅的，但不像其他一些答案那样不言自明。|1691790|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|$]]

Based on java.util.AbstractCollection.toString(), it exits early to avoid the delimiter.

<pre><code>StringBuffer buffer = new StringBuffer();
Iterator iter = s.iterator();
for (;;) {
 buffer.append(iter.next());
 if (! iter.hasNext())
 break;
 buffer.append(delimiter);
}
</code></pre>

It's efficient and elegant, but not as self-evident as some of the other answers.

blocks|key|1476691|text|还有另一个选择。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1476692|StringBuilder+builder+=+new+StringBuilder();
for(int+i+:+array)
++++builder.append(',').append(i);
String+text+=+builder.toString();
if+(text.startsWith(","))+text=text.substring(1);|code-block|syntax|javascript|1476693|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|$]]

Yet another option.

<pre><code>StringBuilder builder = new StringBuilder();
for(int i : array)
 builder.append(',').append(i);
String text = builder.toString();
if (text.startsWith(",")) text=text.substring(1);
</code></pre>

blocks|key|1691854|text|在这种情况下，真的没有必要知道这是否是最后一次重复。我们有很多方法可以解决这个问题。一种方法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1691855|String+del+=+null;
for(int+i+:+array)
{
++++if+(del+!=+null)
+++++++builder.append(del);
++++else
+++++++del+=+",";
++++builder.append(i);
}|code-block|syntax|javascript|1691856|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|$]]

In this case there is really no need to know if it is the last repetition.
There are many ways we can solve this. One way would be:

<pre><code>String del = null;
for(int i : array)
{
 if (del != null)
 builder.append(del);
 else
 del = ",";
 builder.append(i);
}
</code></pre>

blocks|key|1476807|text|正如工具包中提到的，在Java8中，我们现在有了Collectors。下面是代码的样子：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1476808|String+joined+=+array.stream().map(Object::toString).collect(Collectors.joining(",+"));|code-block|syntax|javascript|1476809|我认为这正是您正在寻找的，这是一种模式，您可以将其用于许多其他事情。|1476810|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html^0|O|A|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

As toolkit mentioned, in Java 8 we now have <a href="http://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html" rel="nofollow noreferrer">Collectors</a>. Here's what the code would look like:

<pre><code>String joined = array.stream().map(Object::toString).collect(Collectors.joining(", "));
</code></pre>

I think that does exactly what you're looking for, and it's a pattern you could use for many other things.

blocks|key|1691974|text|由于它是一个固定的数组，它将更容易避免增强的for…如果对象是一个集合，那么迭代器会更简单。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1691975|int+nums[]+=+getNumbersArray();
StringBuilder+builder+=+new+StringBuilder();

//+non+enhanced+version
for(int+i+=+0;+i+<+nums.length;+i%2B%2B){
+++builder.append(nums[i]);
+++if(i+<+nums.length+-+1){
+++++++builder.append(",");
+++}+++
}

//using+iterator
Iterator<int>+numIter+=+Arrays.asList(nums).iterator();

while(numIter.hasNext()){
+++int+num+=+numIter.next();
+++builder.append(num);
+++if(numIter.hasNext()){
++++++builder.append(",");
+++}
}|code-block|syntax|javascript|1691976|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|$]]

Since its a fixed array, it would be easier simply to avoid the enhanced for... If the Object is a collection an iterator would be easier.

<pre><code>int nums[] = getNumbersArray();
StringBuilder builder = new StringBuilder();

// non enhanced version
for(int i = 0; i &lt; nums.length; i++){
 builder.append(nums[i]);
 if(i &lt; nums.length - 1){
 builder.append(",");
 } 
}

//using iterator
Iterator&lt;int&gt; numIter = Arrays.asList(nums).iterator();

while(numIter.hasNext()){
 int num = numIter.next();
 builder.append(num);
 if(numIter.hasNext()){
 builder.append(",");
 }
}
</code></pre>

blocks|key|1691998|text|您可以使用StringJoiner。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1691999|int[]+array+=+{+1,+2,+3+};
StringJoiner+stringJoiner+=+new+StringJoiner(",");

for+(int+i+:+array)+{
++++stringJoiner.add(String.valueOf(i));
}

System.out.println(stringJoiner);|code-block|syntax|javascript|1692000|entityMap|0|LINK|mutability|MUTABLE|url|https://self-learning-java-tutorial.blogspot.com/2015/12/stringjoiner-class.html^0|5|C|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

You can use <a href="https://self-learning-java-tutorial.blogspot.com/2015/12/stringjoiner-class.html" rel="nofollow noreferrer">StringJoiner</a>.
<pre><code>int[] array = { 1, 2, 3 };
StringJoiner stringJoiner = new StringJoiner(&quot;,&quot;);

for (int i : array) {
 stringJoiner.add(String.valueOf(i));
}

System.out.println(stringJoiner);
</code></pre>

Is there a way to determine if the loop is iterating for the last time. My code looks something like this:

<pre><code>int[] array = {1, 2, 3...};
StringBuilder builder = new StringBuilder();

for(int i : array)
{
 builder.append("" + i);
 if(!lastiteration)
 builder.append(",");
}
</code></pre>

Now the thing is I don't want to append the comma in the last iteration. Now is there a way to determine if it is the last iteration or am I stuck with the for loop or using an external counter to keep track.

Last iteration of enhanced for loop in java

有没有一种方法可以确定循环是否最后一次迭代。我的代码看起来像这样：int[] array = {1, 2, 3...};StringBuilder builder = new StringBuilder();for(int i : array){    builder.append("" + i);    if(!la...

问java中增强的for循环的最后一次迭代
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