Two objects value is null; why?

Question

Method parameter sd & ed is LocalDate, I need return date object, but sd & ed return null. My define a private method:

private void setQuarter(LocalDate sd,LocalDate ed,LocalDate today){
            switch (getQuarter(today.getMonthValue())){
                case 1:
                    sd=LocalDate.of(today.getYear(),1,1);
                    ed=LocalDate.of(today.getYear(),3,31);
                    break;
                case 2:
                    sd=LocalDate.of(today.getYear(),4,1);
                    ed=LocalDate.of(today.getYear(),6,30);
                    break;
                case 3:
                    sd=LocalDate.of(today.getYear(),7,1);
                    ed=LocalDate.of(today.getYear(),9,30);
                    break;
                case 4:
                    sd=LocalDate.of(today.getYear(),10,1);
                    ed=LocalDate.of(today.getYear(),12,31);
                    break;
                default:
                    sd=LocalDate.of(today.getYear()+1,1,1);
                    ed=LocalDate.of(today.getYear()+1,1,1);
            }
        }

Invoke this method:

LocalDate sd=null;
LocalDate ed=null;

setQuarter(sd,ed,today);

log.info("==> sd:{},ed:{}",sd,ed);

Output message: ==> sd:null,ed:null

Are you initializing `today`? – bobbyalex Feb 29 '20 at 08:26 — bobbyalex, Feb 29 '20 at 08:26

kozmo · Accepted Answer · 2020-02-29T14:56:46.803

0

Because in Java parameters of methods pass by value. Reference(i.e. a pointer) pass by value of reference(address of the object).

The code should look like this:

Pair<LocalDate, LocalDate> dates = getSdAndEd(today);
LocalDate sd = dates.getLeft();
LocalDate ed = dates.getRight();

private Pair<LocalDate, LocalDate> getSdAndEd(LocalDate today){
    switch (getQuarter(today.getMonthValue())){
        case 1:
            return Pair.of(
                    LocalDate.of(today.getYear(),1,1),
                    LocalDate.of(today.getYear(),3,31)
            )
        case 2:
          ...
    }
}

In example Pair-class from Apache Commons Lang » group: 'org.apache.commons', name: 'commons-lang3', version: '3.9'.

edited Feb 29 '20 at 14:56

answered Feb 29 '20 at 08:27

kozmo

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Why is LocalDate is by value, if parameter is Map, it by value of reference? – fishinhouse Feb 29 '20 at 09:11
LocalDate is the reference -> that right, in parameters of method was copying the value of reference – kozmo Feb 29 '20 at 09:21
Thank you very much answers. – fishinhouse Feb 29 '20 at 16:39

Two objects value is null; why?

1 Answers1