import java.util.regex.Matcher;  import java.util.regex.Pattern;  import java.io.BufferedReader;  import java.io.File;  import java.io.FileReader;  import java.io.IOException;    public class RegularExpression {      public static void main(String[] args) throws IOException {            // Simple expression to find a valid e-mail address in a file          Pattern pattern = Pattern.compile("[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,4}");          // Read file, find valid mail addresses and print result          File file = new File("test.txt");          BufferedReader in = new BufferedReader(new FileReader(file));          int lines = 0;          int matches = 0;          for (String line = in.readLine(); line != null; line = in.readLine()) {              lines++;              Matcher matcher = pattern.matcher(line.toUpperCase());              if (matcher.matches()) {                      System.out.println(lines + ": '" + line + "'");                  matches++;              }          }          // output of summary          if (matches == 0) {                  System.out.println("No matches in " + lines + " lines");          } else {              System.out.println("\n" + matches + " matches in " + lines + " lines");          }      }  }