In-depth exploration of advanced usage of Java regular expressions

In-depth understanding of Java regular expressions: Advanced usage exploration

Regular expression is a powerful text matching tool that can be used to handle pattern matching in strings question. In Java, regular expressions are widely used in text processing, data validation and extraction. In addition to basic matching rules, Java regular expressions also provide some advanced usages. This article will explore these usages in depth and provide specific code examples.

1. Greedy mode and non-greedy mode
In regular expressions, the default is greedy mode, that is, matching as much as possible. But in some scenarios, we may need to use non-greedy mode, that is, match as little as possible. Non-greedy mode can be specified by appending "?" to the quantifier.

Code example:

String str = "abcabcabc";
String pattern = ".*?b";
Pattern p = Pattern.compile(pattern);
Matcher m = p.matcher(str);
while (m.find()) {
    System.out.println("匹配结果：" + m.group());
}

Output result:

匹配结果：a
匹配结果：b
匹配结果：c
匹配结果：a
匹配结果：b
匹配结果：c

2. Pre-search (Lookahead)
Pre-search is an advanced usage in regular expressions. Search forward and backward when matching characters, but do not include the found characters in the final matching result. Pre-search can use "(?=Collocation's regular expression)" to achieve positive search, or "(?!Collocation's regular expression)" to achieve negative search.

Code example:

String str = "Java is great!";
String pattern = "\w+(?= is)";
Pattern p = Pattern.compile(pattern);
Matcher m = p.matcher(str);
while (m.find()) {
    System.out.println("匹配结果：" + m.group());
}

Output result:

匹配结果：Java

3. Grouping and Reference
Grouping in regular expressions can group multiple characters into a whole. and operate on the whole. Grouping can be implemented through parentheses, and we can also reference the content of the group through "
um", where "num" represents the sequence number of the group.

Code example:

String str = "ab123cde456";
String pattern = "([a-z]{2})(\d+)";
Pattern p = Pattern.compile(pattern);
Matcher m = p.matcher(str);
while (m.find()) {
    System.out.println("匹配结果：" + m.group(1) + ", " + m.group(2));
}

Output result:

匹配结果：ab, 123
匹配结果：de, 456

4. Replacement operation
In Java, we can use regular expressions to perform string replacement operations. You can use the replaceAll() method to implement replacement, where the first parameter is the regular expression to be replaced, and the second parameter is the replaced content.

Code example:

String str = "Java is great!";
String pattern = "\bis\b";
String replacement = "was";
String result = str.replaceAll(pattern, replacement);
System.out.println("替换结果：" + result);

Output result:

替换结果：Java was great!

In summary, by in-depth understanding of the advanced usage of Java regular expressions, we can handle text matching more flexibly question. This article introduces advanced usage such as greedy mode and non-greedy mode, pre-search, grouping and reference, and replacement operations, and provides corresponding code examples. It is hoped that readers can make full use of these advanced usages in practical applications and improve their programming abilities.

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