code: public static String getExtension(String fileName) {
  		if (fileName==null){
  			return null;
  		} else {
  			int number=fileName.lastIndexOf('.');
  			
  			if (number>=0){
  				return fileName.substring(number+1, fileName.length());
  			} else {
  				return null;
  			}
  		}		
  	}
docs: If the file is like name.extension This function returns extension
  for filename=name. this returns ""
  for filemane=name  this retuns null;
  for filemane=.extension  this retuns extension;
  for filemane=.  this retuns "";
  
  @param fileNameAndPath
  @return