User should be careful When use acceptChildren() method in the public void preVisit(TExpression node)
or public void postVisit(TExpression node) method of your customzied visitor class that extends TParseTreeVisitor.
class TreeVisitor extends TParseTreeVisitor {
public void preVisit(TExpression node) {
switch (node.getExpressionType()) {
case logical_and_t:
case logical_or_t:
node.getLeftOperand().acceptChildren(this);
node.getRightOperand().acceptChildren(this);
break;
default:
break;
}
}
The above code will cause the left and right sub-expression repeatedly visited, if the expression itself is deeply nested, then the performance will be impacted severely.
Since the acceptChildren() method of TExpression will iterate all sub-expression for you automatically, you shouldn’t call acceptChildren() in the preVisit() method of your own visitor. Only add your business code in the preVisit() method and let the acceptChildren() method of TExpression do the iteration for you.
If you want to iterate all sub-expression in your own code, please use accept() method instead of acceptChildren().
Below is the code of the acceptChildren() method of TExpression for your reference.
public void acceptChildren(TParseTreeVisitor v){
v.preVisit(this);
switch(expressionType){
case simple_object_name_t:
objectOperand.acceptChildren(v);
break;
case list_t:
case collection_constructor_list_t:
case collection_constructor_multiset_t:
case collection_constructor_set_t:
if (exprList != null){
for(int i=0;i<exprList.size();i++){
exprList.getExpression(i).acceptChildren(v);
}
}
break;
case function_t:
case new_structured_type_t:
case type_constructor_t:
functionCall.acceptChildren(v);
break;
case cursor_t:
case subquery_t:
case multiset_t:
subQuery.acceptChildren(v);
break;
case case_t:
caseExpression.acceptChildren(v);
break;
case pattern_matching_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
if (likeEscapeOperand != null){
likeEscapeOperand.acceptChildren(v);
}
break;
case exists_t:
subQuery.acceptChildren(v);
break;
case new_variant_type_t:
newVariantTypeArgumentList.acceptChildren(v);
break;
case unary_plus_t:
case unary_minus_t:
case unary_prior_t:
rightOperand.acceptChildren(v);
break;
case arithmetic_plus_t:
case arithmetic_minus_t:
case arithmetic_times_t:
case arithmetic_divide_t:
case power_t:
case range_t:
case concatenate_t:
case period_ldiff_t:
case period_rdiff_t:
case period_p_intersect_t:
case period_p_normalize_t:
case contains_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case assignment_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case sqlserver_proprietary_column_alias_t:
rightOperand.acceptChildren(v);
break;
case arithmetic_modulo_t:
case bitwise_exclusive_or_t:
case bitwise_or_t:
case bitwise_and_t:
case bitwise_xor_t:
case exponentiate_t:
case scope_resolution_t:
case at_time_zone_t:
case member_of_t:
case arithmetic_exponentiation_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case at_local_t:
case day_to_second_t:
case year_to_month_t:
leftOperand.acceptChildren(v);
break;
case parenthesis_t:
leftOperand.acceptChildren(v);
break;
case simple_comparison_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case group_comparison_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case in_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case floating_point_t:
leftOperand.acceptChildren(v);
break;
case logical_and_t:
case logical_or_t:
case logical_xor_t:
case is_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case logical_not_t:
rightOperand.acceptChildren(v);
break;
case null_t:
leftOperand.acceptChildren(v);
break;
case between_t:
if (betweenOperand != null){
betweenOperand.acceptChildren(v);
}
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case is_of_type_t:
leftOperand.acceptChildren(v);
break;
case collate_t: //sql server,postgresql
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case left_join_t:
case right_join_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case ref_arrow_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case typecast_t:
leftOperand.acceptChildren(v);
break;
case arrayaccess_t:
arrayAccess.acceptChildren(v);
break;
case unary_connect_by_root_t:
rightOperand.acceptChildren(v);
break;
case interval_t:
intervalExpr.acceptChildren(v);
break;
case unary_binary_operator_t:
rightOperand.acceptChildren(v);
break;
case left_shift_t:
case right_shift_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case array_constructor_t:
if (subQuery != null){
subQuery.acceptChildren(v);
}else if (exprList != null){
exprList.acceptChildren(v);
}else if (arrayConstruct != null){
arrayConstruct.acceptChildren(v);
}
break;
case row_constructor_t:
if (exprList != null){
exprList.acceptChildren(v);
}
break;
case unary_squareroot_t:
case unary_cuberoot_t:
case unary_factorialprefix_t:
case unary_absolutevalue_t:
case unary_bitwise_not_t:
getRightOperand().acceptChildren(v);
break;
case unary_factorial_t:
getLeftOperand().acceptChildren(v);
break;
case bitwise_shift_left_t:
case bitwise_shift_right_t:
getLeftOperand().acceptChildren(v);
getRightOperand().acceptChildren(v);
break;
case multiset_union_t:
case multiset_union_distinct_t:
case multiset_intersect_t:
case multiset_intersect_distinct_t:
case multiset_except_t:
case multiset_except_distinct_t:
getLeftOperand().acceptChildren(v);
getRightOperand().acceptChildren(v);
break;
case json_get_text:
case json_get_text_at_path:
case json_get_object:
case json_get_object_at_path:
case json_left_contain:
case json_right_contain:
case json_exist:
case json_any_exist:
case json_all_exist:
getLeftOperand().acceptChildren(v);
getRightOperand().acceptChildren(v);
break;
case interpolate_previous_value_t:
getLeftOperand().acceptChildren(v);
getRightOperand().acceptChildren(v);
break;
case submultiset_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case overlaps_t:
leftOperand.acceptChildren(v);
rightOperand.acceptChildren(v);
break;
case is_a_set_t:
leftOperand.acceptChildren(v);
break;
case array_t:
if (getExprList() != null){
getExprList().acceptChildren(v);
}
break;
default:;
}
v.postVisit(this);
}