Show HN: I Wrote a Book on Java

Re:Show HN: I Wrote a Book on Java by kentosi on Monday September 23, 2024 @08:50PM (#41632064)

I haven't yet had the luxury to experiment with the latest version of Java, but this is one of the reasons why I wish Java introduced named parameters the say way kotlin and scala do.

Eg:

  data class Make(makeId: String, name: String)
  data class Model(modelId: String, name: String)

  data class Car(make: Make, model: Model, year: String, ...)

Now you can go ahead and order the params whichever way you wish so long as you're explicitly naming them:

  val v1 = Car(make = myMake1, model = myModel1, year = "2023", ...)
  val v1 = Car(model = myModel1, make = myMake1, year = "2023", ...)

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Re:Show HN: I Wrote a Book on Java by Ironlink on Tuesday September 24, 2024 @05:29AM (#41634744)

Once withers land, I think you could approximate this by letting your record class have a zero argument constructor which sets every field to some blank value, and then fill the fields using `with`.

  var x = new Car() with { make = "Volvo"; year = "2023"; };

If you want the Car constructor to enforce constraints, you could use this pattern in a separate Builder record:

  record Car(String make, String year) {
    Car {
      Objects.requireNonNull(make);
      Objects.requireNonNull(year);
    }

    record Builder(String make, String year) {
      Builder() {
        this(null, null);
      }
      Car build() {
        return new Car(make, year);
      }
    }
  }

  var x = new Car.Builder() with { make = "Volvo"; year = "2023"; }.build();

Obviously syntax TBD.

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Re:Show HN: I Wrote a Book on Java by Tainnor on Tuesday September 24, 2024 @05:50PM (#41641318)

So much syntax to enable something that other languages have had for 10+ years. That's why I can't take the "Java is as good as Kotlin now" arguments seriously.

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Re:Show HN: I Wrote a Book on Java by javanonymous on Tuesday September 24, 2024 @07:06AM (#41635269)

I think named parameters would be a great addition

For now, I use Lombok's @Builder annotation. It makes it much easier to create and copy a record, where non-assigned attributes are set to default.

Example:

   var bmw = Car.builder().make("BMW").build()

It also has a practical toBuilder() syntax that creates a copy of the original record, with some attributes changed

   var other = bmw.toBuilder().year(2024).build()

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