Suppose we have a multi-line string that represents a code snippet:

String codeSnippet = "public class HelloWorld {\n" +
                     "    public static void main(String[] args) {\n" +
                     "        System.out.println(\"Hello, World!\");\n" +
                     "    }\n" +
                     "}";

We want to extract the method signature and its content from this code snippet. To do this using regular expressions in Java, we can use the Pattern and Matcher classes. Here’s a code snippet that demonstrates this:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexExample {
    public static void main(String[] args) {
        String codeSnippet = "public class HelloWorld {\n" +
                             "    public static void main(String[] args) {\n" +
                             "        System.out.println(\"Hello, World!\");\n" +
                             "    }\n" +
                             "}";

        String pattern = "public static void main\\(String\\[] args\\) \\{(.+?)\\}";

        // Compile the regular expression pattern
        Pattern regex = Pattern.compile(pattern, Pattern.DOTALL | Pattern.MULTILINE);

        // Match the pattern against the code snippet
        Matcher matcher = regex.matcher(codeSnippet);

        if (matcher.find()) {
            // Extract the matched content
            String methodContent = matcher.group(1);
            System.out.println("Method Content:\n" + methodContent);
        }
    }
}

In this example, we’ve defined a regular expression pattern public static void main\\(String\\[] args\\) \\{(.+?)\\}. This pattern matches the method signature public static void main(String[] args) { and captures the content inside the curly braces using parentheses (.*?).

By using the Pattern.MULTILINE flag, the . character in the pattern will match any character, including line terminators. The Pattern.DOTALL flag ensures that the . character can match line terminators as well.

The Matcher class is used to match the pattern against the code snippet. If a match is found, we can extract the content of the method using the matcher.group(1) method.

Remember to import the necessary classes java.util.regex.Matcher and java.util.regex.Pattern before running the code.

Using the Pattern.MULTILINE flag along with appropriate regular expressions allows you to match patterns across multiple lines in Java. Make sure to test your regular expressions thoroughly to cover different scenarios and edge cases.

#Java #RegularExpressions