Local variable i defined in an enclosing scope must be final or effectively final

Question

I want to implement this endpoint with internal search:

@PostMapping("terminals_risk_filter/change_order/{terminalId}")
    public ResponseEntity<?> updateFiltersPositions(@PathVariable Integer terminalId,
            @RequestBody List<ChangeOrderRiskFiltersDTO> newFiltersPositionsList) {

        List<RiskFilters> filterList = riskFilterService.findRiskFiltersByTerminalId(terminalId);

        for (int i = 0; i < newFiltersPositionsList.size(); i++) {
//          RiskFilters filter = filterList.findById(newFiltersPositionsList.get(i).getId());

            Optional<RiskFilters> filter_payload = filterList.stream().filter(f -> newFiltersPositionsList.get(i).getId() == f.getId()).findAny();
            RiskFilters filter = filter_payload.get();      

            filter.setPosition(newFiltersPositionsList.get(i).getPosition());
            riskFilterService.save(filter);
        }
        return ok().build();
    }

But I get error message Local variable i defined in an enclosing scope must be final or effectively final Can you give me some advice how I can fix this issue, please? For example can I skip the for cycle and use maybe stream into stream?

Answer 1

Can you give me some advice how I can fix this issue, please?

Why does this happen? You can read about it here: Lambdas: local variables need final, instance variables don't

Minimal changes to solve your problem: Don't use the i variable itself. Create a copy of it and make it final.

final int iCopy = i;
Optional<RiskFilters> filter_payload = filterList.stream().filter(f -> newFiltersPositionsList.get(iCopy).getId() == f.getId()).findAny();

For example can I skip the for cycle and use maybe stream into stream?

You could give it a try:

// replace the for-loop

// or just.... `newFiltersPositionsList.forEach(/* ... */)`
newFiltersPositionsList.stream().forEach(filterPosition -> {
    Optional<RiskFilters> filter_payload = filterList.stream()
            .filter(f -> filterPosition.getId() == f.getId())
            .findAny();
    RiskFilters filter = filter_payload.get();

    filter.setPosition(filterPosition.getPosition());
    riskFilterService.save(filter);
});

Also, you could use a for-each instead of a for-loop:

for (ChangeOrderRiskFiltersDTO filterPosition : newFiltersPositionsList) {
    Optional<RiskFilters> filter_payload = filterList.stream()
           .filter(f -> filterPosition.getId() == f.getId())
           .findAny();
    RiskFilters filter = filter_payload.get();
    filter.setPosition(filterPosition.getPosition());
    riskFilterService.save(filter);
}

Answer 2

You can do it like below as well.

final ChangeOrderRiskFiltersDTO dto = newFiltersPositionsList.get(i);
Optional<RiskFilters> filter_payload = filterList.stream().filter(f -> dto.getId() == f.getId()).findAny();
if(filter_payload.isPresent()){
  RiskFilters filter = filter_payload.get();
  //More operations
}