Recursively looping into directories and subdirectories to get files that matching with pattern

1. import java.io.File;
2. import java.util.ArrayList;
3. import java.util.List;
4. import java.util.regex.*;
6. public class TechFact555FileMatching {
7.   // Pattern to match with file name
8.   public static final String FILE_PATTERN = "[a-zA-Z0-9]{6}";
9.  
10.   public static void main(String[] args) {
11.     List<File> resultFiles = new ArrayList<>();
12.     TechFact555FileMatching fileMatching = new TechFact555FileMatching();
13.     
14.     // Specify parent folder to fetch files
15.     fileMatching.listFiles(new File("E:/folder"), resultFiles);
16.    
17.     for (File resultFile : resultFiles) {
18.       System.out.print(resultFile.getName());
19.     }
20.   }
21.  
22.   // Recursively looping into folders to get Files
23.   void listFiles(File directory, List<File> filesList) {
24.     File[] filesAndFoldersList = directory.listFiles();
25.     if (filesAndFoldersList != null) {
26.       for (File fileOrFolder : filesAndFoldersList) {
27.         if (fileOrFolder.isDirectory()) {
28.           listFiles(fileOrFolder, filesList);
29.         } else if (fileOrFolder.isFile() && Pattern.matches(FILE_PATTERN, fileOrFolder.getName())) {
30.           filesList.add(fileOrFolder);
31.         }
32.       }
33.     }
34.   }
35. }

Pass the Directory to fetch files as first parameter and list of files to add the pattern matching pattern as second parameter into listFiles function.