java - 结合两个java正则表达式

Question

不得不第一次使用正则表达式，尽管我几乎达到了我的要求，但我似乎无法将其组合成一个语句。

我有一串单词，如果它前面没有点或前面没有点空格，我希望替换 \n。

我可以运行这两个语句中的任何一个来获得所需的结果。但是，如果我一个接一个地运行它们或尝试将它们组合成一个正则表达式，它就不起作用。

//replaces \n if not preceded by dot space
xx = xx.replaceAll("(.+)(?<!\\. )\n", "$1 ");


//replaces \n if not preceded by dot
xx = xx.replaceAll("(.+)(?<!\\.)\n", "$1 "); 


//one of my attempts to combine into a single statement
xx = xx.replaceAll("(.+)(?<!\\. )\n|(?<!\\.)\n", "$1 ");

我正在尝试修复的字符串示例。

之前

This is some text which may\n
have a newline character to break the line\n
but I only want to remove it if it's not preceded with a full.\n
or it's not preceded with a full stop and a space. \n

之后

This is some text which may
have a newline character to break the line 
but I only want to remove it if it's not preceded with a full.\n
or it's not preceded with a full stop and a space. \n

我想我已经很接近了，但是作为正则表达式的新手，我读得越多就越困惑。

Answer 1

这比你想象的要容易:

String resultString = subjectString.replaceAll("(?<!\\. ?)\n", " ");

解释:

(?<!   # Assert that the previous characters are not...
 \.    # a dot
 [ ]?  # optionally followed by a space
)      # End of lookbehind
\n     # Match a newline character

所以你不需要首先匹配 (.+) ，只需要在之后用它自己替换它。顺便说一下，这是让你绊倒的原因:

(.+)(?<!\. )\n|(?<!\.)\n

在逻辑上被分组为

(.+)(?<!\. )\n   # Match this
|                # or
(?<!\.)\n        # this

因此 (.+) 仅在点后没有空格时匹配。