import java.util.regex.Pattern;

import java.util.regex.Matcher;

import java.util.regex.PatternSyntaxException;

public class RegexDemo{

public static void main(String[] args){

if(args.length != 2){

System.err.println("usage: java RegexDemo regex input");

return;

}

System.out.println("regex = " + args[0]);

System.out.println("input = " + args[1]);

try{

Pattern pattern = Pattern.compile(args[0]);

Matcher matcher = pattern.matcher(args[1]);

while(matcher.find()){

System.out.println("Located [" + matcher.group() + "] starting at " + matcher.start() + " and ending at " + (matcher.end()-1));

// need to understand the methods return values.

}

}catch(PatternSyntaxException pse){

System.err.println("Bad regex: " + pse.getMessage());

System.err.println("Description: " + pse.getDescription());

System.err.println("Index: " + pse.getIndex());

System.err.println("Incorrect pattern: " + pse.getPattern());

}

}

}