Java支持条件超前 [英] Java support for conditional lookahead

问题描述

在下面，让我说邮政编码，我试图从结果中排除33333-.
我愿意:

In the following let's say zip codes I am trying to exclude the 33333- from the result.
I do:

String zip = "11111 22222 33333- 44444-4444";
String regex = "\\d{5}(?(?=-)-\\d{4})";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(zip);
while (matcher.find()) { 
   System.out.println(" Found: " + matcher.group());     
}

期望得到:

Found:  11111  
Found:  22222  
Found:  44444-4444

我正在尝试强制采用以下格式:
5位数字(可选)，后跟-和4位数字.不需要只带有-(连字符)的5位数字

I am trying to enforce format of:
5 digits optionally followed by a - and 4 digits. 5 digits with just a - (hyphen) is not wanted

我得到异常:

Exception in thread "main" java.util.regex.PatternSyntaxException: Unknown inline modifier near index 7
\d{5}(?(?=-)(-\d{4}))
       ^
    at java.util.regex.Pattern.error(Unknown Source)
    at java.util.regex.Pattern.group0(Unknown Source)
    at java.util.regex.Pattern.sequence(Unknown Source)
    at java.util.regex.Pattern.expr(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.util.regex.Pattern.<init>(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)

我没有正确使用条件超前吗?

Am I not using the conditional lookahead correctly?

推荐答案

要捕获除33333以外的所有数字，请使用以下代码:

To capture all numbers except 33333 use this code:

String zip = "11111 22222 33333- 44444-4444";
String regex = "\\d{5}(?=(-\\d{4}|\\s|$))(-\\d{4})?";
Matcher m = Pattern.compile(regex).matcher(zip);
while(m.find())
    System.out.printf("Macthed: [%s]%n", m.group(1));

输出:

Macthed: [11111]
Macthed: [22222]
Macthed: [44444-4444]

说明::此RegEx使用的前瞻性本身就像一个条件，这意味着匹配5位数字，必须跟-和4位数字或空格或字符串末尾，然后是(可选)匹配文本和4位数字.

Explanation: This RegEx is using lookahead that itself is like a condition, which means match 5 digit number which must be followed by - and 4 digits OR a space OR end of string and then it is optionally matching a text - and 4 digits.

原始RegEx之所以抛出异常是因为RegEx的?:(?=-)部分存在语法错误.

The reason why your original RegEx is throwing exception because there is a syntax error in ?:(?=-) part of your RegEx.

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