How to find and match just one element list in the java stream?

Meysam Zarei :

I have a list that contains some home numbers, and they have 'isPrimary' and 'number' properties.

"homeNumbers": [
      {
        "isPrimary": true,
        "number": "9999999999"
      },
      {
        "isPrimary": false,
        "number": "9999999323"
      }
    ]

Now, I want to write two conditions on the list to match ONLY one of them, I mean this list must have one primary number and its number mustn't be null.

I have written below code but it just checks whether there is any primary number or not, Now, I want to know how to expand it to check just one of them is primary.

private boolean isSetPrimaryHomeNumber(UpdateWorkerDto updateWorkerDto) {
    return updateWorkerDto.getPhoneNumbers().getHomeNumbers().stream().anyMatch(
            number -> Objects.requireNonNullElse(number.getIsPrimary(), false) && !number.getNumber().isEmpty());
}

Nicktar :

You could filter by primary numberst first and then filter those again for Non-Null numbers, then count and compare to 1 like this:

boolean isValid(List<HomeNumber> numbers) {
    return numbers.stream()
                  .filter(HomeNumber::isPrimary)
                  .filter(n -> Objects.notNull(n.getNumber()))
                  .count() == 1;
}