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How can I update an item the arraylist using stream, example I want to update item 1 from 100 to 1000:

    List<PayList> payList = new ArrayList<>();
    payList.add(new PayList(1, 100));
    payList.add(new PayList(2, 200));

I am able to find the index, but how can I find the index and then update the value?

   int indexOf = IntStream.range(0, payList.size())
                            .filter(p -> trx.getTransactionId() == 
   payList.get(p).getTransactionId())
                            .findFirst().orElse(-1);
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  • Is PayList mutable? Does it have a method like setAmount to update 100 to 1000? Commented Jun 13, 2021 at 2:53
  • @roby it's not mutable, yes it has setAmount method. Commented Jun 13, 2021 at 2:53

1 Answer 1

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A couple of options:

Using the index you have already obtained, you can use paylist.get(index) again. However you must handle the missing -1 case:

int indexOf = IntStream.range(0, payList.size())
                       .filter(p -> trx.getTransactionId() ==
                                    payList.get(p).getTransactionId())
                       .findFirst().orElse(-1);
if(indexOf == -1) {
    // handle missing
}else {
    payList.get(indexOf).setAmount(1000);
}

If you don't need to handle the missing case you could stream over the lists like this:

final Stream<PayList> filtered = payList.stream().filter(p -> trx.getTransactionId() == p.getTransactionId());
final Optional<PayList> first = filtered.findFirst();
first.ifPresent(i -> i.setAmount(1000));

Or you could use similar orElse, ifPresentOrElse, orElseThrow type logic on the optional to handle the missing case.

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