private static int digitSum ( int n ) {
  if ( n < 0 ) throw new IllegalArgumentException ( ) ;
  int result = 0 ;
  while ( n != 0 ) {
    result += n % 10 ;
    n /= 10 ;
  }
  return result ;
}

private static int digitSum ( int n ) { if ( n < 0 ) throw new IllegalArgumentException ( ) ; int result = 0 ; while ( n != 0 ) { result += n % 10 ; n /= 10 ; } return result ; }
(method_declaration (modifiers) type: (integral_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (integral_type) name: (identifier))) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (throw_statement (object_creation_expression type: (type_identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (while_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) body: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))) (expression_statement (assignment_expression left: (identifier) right: (decimal_integer_literal))))) (return_statement (identifier))))