How to use Java regex to extract a specific substring.

The general steps for using Java regular expressions to extract specified strings are as follows:

1. Import the package for Java regular expressions: import java.util.regex.*;
2. Define a regular expression pattern by using the Pattern.compile() method to create a Pattern object and passing the regular expression as a parameter.
3. Create a Matcher object: Use the matcher() method of the Pattern object to create a Matcher object, passing the string to be matched as a parameter.
4. Perform matching and extraction: Use the find() and group() methods of the Matcher object for matching and extraction.

Here is an example of using regular expressions to extract a specific string:

import java.util.regex.*;

public class RegexExample {
    public static void main(String[] args) {
        String input = "Hello, my name is John. I am 25 years old.";
        
        // 定义正则表达式模式
        Pattern pattern = Pattern.compile("\\b\\w+\\b");
        
        // 创建Matcher对象
        Matcher matcher = pattern.matcher(input);
        
        // 进行匹配和截取
        while (matcher.find()) {
            String match = matcher.group();
            System.out.println(match);
        }
    }
}

The code above will print out each word in the input string. The regular expression pattern \\b\\w+\\b matches one or more alphanumeric characters, words. The matcher.find() method searches for the next match in the input string, while the matcher.group() method returns the string representation of the match. Within the loop, we print out each match.

According to your specific needs, you can modify the pattern based on the rules of regular expressions to extract different specified strings.