java 在特定位置附加到字符串
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Append to String at certain position
提问by maddy
I have a String miscFlag which is of size 100. I need to append to this miscFlag starting from index 20 as 0-19 are reserved for some other info. And then append subsequently at certain positions only. Can we do this using StringBuilder/StringBuffer?
我有一个大小为 100 的 String miscFlag。我需要从索引 20 开始附加到这个 miscFlag，因为 0-19 是为其他一些信息保留的。然后仅在某些位置随后附加。我们可以使用 StringBuilder/StringBuffer 来做到这一点吗？
This is how i am trying to do it..
这就是我正在尝试这样做的方式..
StringBuilder info = new StringBuilder(miscFlag);
info.append(" ");
info.append(Misc.toTimestampLiteral(currentDate));//append this from pos 20
info.append(" ");
info.append(formattedStartTime); //append this from pos 40
Here i am not able to specify the position from where to append.
在这里我无法指定从哪里追加的位置。
回答by Farmor
Use the insert method.
使用插入方法。
info.insert(19, Misc.toTimestampLiteral(currentDate));
回答by Subhrajyoti Majumder
Use String#subStringto cut 0 to 20 index and then add new String.
使用String#subString削减0至20索引，然后添加新的字符串。
String str = miscFlag.substring(0,20)+ " "+Misc.toTimestampLiteral(currentDate)+" "+ miscFlag.substring(21);
回答by Audrius Meskauskas
Fixed length fields are doable with StringBuilderbut looks for me very clumsy and error-prone, I would not recommend. Use String.format, it is exactly for that you need - to create string where field widths and positions are important:
固定长度字段是可行的，StringBuilder但看起来我很笨拙且容易出错，我不推荐。使用String.format，它正是您需要的 - 创建字段宽度和位置很重要的字符串：
String.format("A[%8s][%4s]", "ab","cd");
will result
将导致
A[ ab][ cd]
回答by Chaitanya K
You can specify the sposition where you'd like to insert as below
您可以指定要插入的位置，如下所示
StringBuilder info = new StringBuilder(miscFlag);
info.insert(19, Misc.toTimestampLiteral(currentDate) + " ");
info.insert(39, formattedStartTime + " ");
