代码语言：javascript复制
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");
}
}
}</pre> 
