The below code shows how to use the class

import druva.emailValidator;

trace('druva.flash@gmail.com > '+emailValidator.isValid('druva.flash@gmail.com'));
// true
trace('druva.flash@gmail > '+emailValidator.isValid('druva.flash@gmail'));
// false
trace('druva.@.com > '+emailValidator.isValid('druva.@.com'));
//false
trace('druva.@gmail.com > '+emailValidator.isValid('druva.@gmail.com'));
//true
trace('.aa@gmailcom > '+emailValidator.isValid('.aa@gmailcom'));
//false

This is the actual class for validation

package druva {
  import flash.display.Sprite;

  public class emailValidator extends Sprite{
    public function emailValidator(){
    }

    public static function isValid(em:String):Boolean {

        var sEmail:String = new String(em);
        var validEmail:Boolean = true;
        var numDotPos:int = sEmail.indexOf("@");
        var nDotIndex:int = sEmail.lastIndexOf(".");
        if(numDotPos == -1 || nDotIndex == -1) {
          validEmail = false;
        }
        if(!(numDotPos > 0)) {
          validEmail = false;
        }
          if(!(nDotIndex > numDotPos)) {
        validEmail = false;
        }
        if(!(numDotPos < sEmail.length - 1) || !(nDotIndex > numDotPos + 1)) {
          validEmail = false;
        }
        return validEmail;
    }

  }
}

This code show how to convert string case to upper and to lower.
And also shows how to compare two strings and returns index value.

var site:String = "http://blog.totusinfo.com";

var siteUp:String = site.toUpperCase();
var siteLow:String = site.toLowerCase();

trace(siteUp.indexOf('totus'));
trace(siteLow.indexOf('totus'));

This code show how to create instance of a string.
And this code shows how to concatenate two strings.

var a:String = "vineela";
var b:String = a;
a = "Druva";
trace(a.concat(b)); 

package com.druva.util {

   public class StringUtils {
	public static removeExtraWhitespace(p_string:String):String {
	   if (p_string == null) { return ''; }
	   var str:String = trim(p_string);
	   return str.replace(/\s+/g, ' ');
	}
	public static function trim(p_string:String):String {
	   if (p_string == null) { return ''; }
	   return p_string.replace(/^\s+|\s+$/g, '');
	}
}