迭代两个列表并从第一个列表中设置元素

Question

I have two ArrayList as below -

certificates=[CERT1, CERT2]
promotions=[{type}, {type, promotionCode}, {type, promotionCode}]

promotions list size is not confirm but certificates list size is confirmed. So consider first list size is 2 and second list size is 3

I want to set promotionCode in second list from certificates but in second list some time promotionCode is not present.

for (int i = 0; i < getCertificateNumber().size(); i++) {
   if (!promotions().isEmpty()) {
       promotions().get(i).setPromotionCode(getCertificateNumber().get(i));
   }
}

as in above for loop it set only first two promotions in promotion list because certificate list size two

How can I avoid any element from second list which don't have promotionCode and set CERT to element which has promotionCode

Answer 1

You can add an if statement to check if the promotion code is not null, in this way to avoid getting beyong CERT1:

int i = 0;
for ( Promotion prom : promotions ) {
    // check if promotioncode is not null
    if( prom.getPromotionCode() != null ) {
       prom.setPromotionCode(getCertificateNumber().get(i));
       i++; // increments only if not null
 }
}

Answer 2

This code will filter out promotions without codes and limit it to the number of certs we have. Then you can run your for loop to map the codes to valid promotions. Also, in this case I would run the for loop over validPromotions , not certificates , because we might not have any valid promotions.

    List<Promotion> validPromotions = promotions.stream()
            .filter(x -> x.promotionCode != null) // only keep promotions that have valid promotion codes
            .limit(certificates.length) // only keep as many promotions as we have certificates for
            .collect(Collectors.toList());