import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class IPAddressValidator{

    private Pattern pattern;

    private Matcher matcher;

    private static final String IPADDRESS_PATTERN =

		"^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +

		"([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +

		"([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +

		"([01]?\\d\\d?|2[0-4]\\d|25[0-5])$";

    public IPAddressValidator(){

	  pattern = Pattern.compile(IPADDRESS_PATTERN);

    }

   /**

    * Validate ip address with regular expression

    * @param ip ip address for validation

    * @return true valid ip address, false invalid ip address

    */

    public boolean validate(final String ip){

	  matcher = pattern.matcher(ip);

	  return matcher.matches();

    }

}

^		#start of the line

 (		#  start of group #1

   [01]?\\d\\d? #    Can be one or two digits. If three digits appear, it must start either 0 or 1

		#    e.g ([0-9], [0-9][0-9],[0-1][0-9][0-9])

    |		#    ...or

   2[0-4]\\d	#    start with 2, follow by 0-4 and end with any digit (2[0-4][0-9])

    |           #    ...or

   25[0-5]      #    start with 2, follow by 5 and ends with 0-5 (25[0-5])

 )		#  end of group #2

  \.            #  follow by a dot "."

....            # repeat with 3 times (3x)

$		#end of the line