Using REGEX

Summary of Regular Expression Constructs

(Source: Oracle Website)

Characters
width="132"x	The character x
\\	The backslash character
\0n	The character with octal value 0n (0 <= n <= 7)
\0nn	The character with octal value 0nn (0 <= n <= 7)
\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\x{h…h}	The character with hexadecimal value 0xh…h (Character.MIN_CODE_POINT <= 0xh…h <= Character.MAX_CODE_POINT)
\t	The tab character (‘\u0009’)
\n	The newline (line feed) character (‘\u000A’)
\r	The carriage-return character (‘\u000D’)
\f	The form-feed character (‘\u000C’)
\a	The alert (bell) character (‘\u0007’)
\e	The escape character (‘\u001B’)
\cx	The control character corresponding to x

Character classes
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)

Predefined character classes
.	Any character (may or may not match line terminators)
\d	A digit: [0-9]
\D	A non-digit: [^0-9]
\s	A whitespace character: [ \t\n\x0B\f\r]
\S	A non-whitespace character: [^\s]
\w	A word character: [a-zA-Z_0-9]
\W	A non-word character: [^\w]

Boundary matchers
^	The beginning of a line
$	The end of a line
\b	A word boundary
\B	A non-word boundary
\A	The beginning of the input
\G	The end of the previous match
\Z	The end of the input but for the final terminator, if any
\z	The end of the input

Example:

 import java.util.regex.Matcher;  
 import java.util.regex.Pattern;  
 public class RegexMatchesSample  
 {  
      private static String pattern = "^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";  
      private static Pattern customPattern = Pattern.compile(pattern);  
      public static void main( String args[] ){  
           String validEmail1 = "testemail@domain.com";  
           String validEmail2 = "test.email@domain.com";  
           String invalidEmail1 = "....@domain.com";  
           String invalidEmail2 = ".$$%%@domain.com";  
           System.out.println("Is Email ID : '" + validEmail1+ "' valid? - "+validateEmailID(validEmail1));  
           System.out.println("Is Email ID : '" + validEmail2+ "' valid? - "+validateEmailID(validEmail2));  
           System.out.println("Is Email ID : '" + invalidEmail1+ "' valid? - "+validateEmailID(invalidEmail1));  
           System.out.println("Is Email ID : '" + invalidEmail2+ "' valid? - "+validateEmailID(invalidEmail2));  
      }  
      public static boolean validateEmailID(String emailID) {  
           Matcher mtch = customPattern.matcher(emailID);  
           if(mtch.matches()){  
                return true;  
           }  
           return false;  
      }        
 }  

Result:
Is Email ID : 'testemail@domain.com' valid? - true
Is Email ID : 'test.email@domain.com' valid? - true
Is Email ID : '....@domain.com? - false
Is Email ID : '.$$%%@domain.com' valid? - false