code: private static boolean isValidJavaIdentifier(final String identifier) {
      Contracts.assertNotNull(identifier, "identifier param cannot be null");
  
      if (identifier.length() == 0 || !isJavaIdentifierStart(identifier.charAt(0))) {
        return false;
      }
  
      for (int i = 1; i < identifier.length(); i++) {
        if (!isJavaIdentifierPart(identifier.charAt(i))) {
          return false;
        }
      }
      return true;
    }
docs: Validate that the given identifier is a valid Java identifier according to the Java Language.
  Specification,
  <a href="http://docs.oracle.com/javase/specs/jls/se6/html/lexical.html#3.8">chapter 3.8</a>
  
  @param identifier string identifier to validate
  
  @return true if the given identifier is a valid Java Identifier
  
  @throws IllegalArgumentException if the given identifier is {@code null}