通过Java中的for-each循环检测第一次迭代 [英] Detecting the first iteration through a for-each loop in Java

问题描述

我正在处理一个服务器，它将字符分隔的列表返回给客户端。
为了构建这些列表，我必须通过一个for-each循环来检测第一个迭代：
$ b $ pre $ String $ builder builder = new StringBuilder（）;
boolean firstIterationFlag = true;

（String s：list）{
if（firstIterationFlag）{
firstIterationFlag = false;
} else {
builder.append（separator）;
}
builder.append（s）;
}
return builder.toString（）;

有没有这样做的方式没有国旗？

$ b $

  //对于第一次迭代，使用无操作分隔符
 String currentSeparator =; 
 for（String s：list）{
 builder.append（currentSeparator）; 
 builder.append（s）; 
 //从第二次迭代开始，使用
 currentSeparator = separator; 
 
 $ / code> 

或者（最好是）使用Guava的 Joiner 类开始：）



这个joiner场景几乎总是 给出的这个需求 - 所以只需使用木。对于其他场景，请使用常规的 for 循环或根据您的代码使用条件。

I'm working on a server that returns character separated lists to its client. In order to build these lists I have to detect the first iteration through a for-each loop:

    StringBuilder builder = new StringBuilder() ;
    boolean firstIterationFlag = true ;

    for ( String s : list ){
        if ( firstIterationFlag) {
            firstIterationFlag = false ;
        } else {
            builder.append(separator);
        }
        builder.append(s) ;         
   }
   return builder.toString() ;

Is there a way of doing this without the flag?

解决方案

One simpler way for this situation is to note that you can always append an empty string:

// For the first iteration, use a no-op separator
String currentSeparator = "";
for (String s : list) {
    builder.append(currentSeparator);
    builder.append(s);
    // From the second iteration onwards, use this
    currentSeparator = separator;
}

Alternatively (and preferrably) use Guava's Joiner class to start with :)

This "joiner" scenario is almost always the one given for this requirement - so just use Joiner. For other scenarios, either use a regular for loop or use the condition as per your code.

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