public static boolean isAlphaNumeric ( String s ) {
  return s != null && s . matches ( "^[a-zA-Z0-9]*$" ) ;
}

public static boolean isAlphaNumeric ( String s ) { return s != null && s . matches ( " ^ [ a - zA - Z0-9 ] * $ " ) ; }
(method_declaration (modifiers) type: (boolean_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier))) body: (block (return_statement (binary_expression left: (binary_expression left: (identifier) right: (null_literal)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (string_literal)))))))