Record canonical constructor is required to be public

[Remi Forax]

I  know we already discuss that but i still don't understand why  a canonical constructor has to be public.

I understand that a canonical constructor is not a simple constructor because it is also used as a kind of default de-constructor, but this doesn't work well with the current rules for constructors in nested classes/enums and if the class is not visible, it's constructor is not visible anyway.

As Brian said in its presentation at Devoxx, records can be used to represent local nominal tuples, like

  public void foo() {
    record Pair(String name, int value);
    ...
  }

If one want to add a requireNonNull using a compact constructor, it will be
  public void foo() {
    record Pair(String name, int value) {
      public Pair {
        Objects.requireNonNull(name);
      }
    }
    ...
  }

having to declare the constructor to be public in that case seems weird. 

Mandating that the canonical constructor (hence the compact constructor) to be public:
- goes against the idea of encapsulation that a constructor like any members should be the least visible
- goes against the rules of default constructors (default constructor use the same visibility as their class) [1]
- goes against the rules of constructors in enums (use private or package private depending on the kind of enums) [2]

So we a set of rules in the JLS that follows the idea that a constructor should not be public by default in nested classes [1] but the rule for a canonical constructor doesn't follow the same idea [3], this should be fixed.

In my opinion, the rule for a canonical constructor should be the same as the rule for a default constructor.

regards,
Rémi


[1] https://docs.oracle.com/javase/specs/jls/se13/html/jls-8.html#jls-8.8.9
[2] https://docs.oracle.com/javase/specs/jls/se13/html/jls-8.html#jls-8.9.2
[3] http://cr.openjdk.java.net/~gbierman/jep359/jep359-20191031/specs/records-jls.html#jls-8.10.4