Records, enums & Optional: interview questions & scenarios

Model answer

A final class that extends java.lang.Record, with:

• two private final int fields, x and y;
• a canonical constructor Point(int x, int y) that assigns them;
• public accessors x() and y() (not getX());
• value-based equals, hashCode and toString, so new Point(1, 2).equals(new Point(1, 2)) is true and it prints Point[x=1, y=2].

Because it already extends Record and is final, a record can't extend another class or be extended. It can implement interfaces and declare static members and instance methods.

Model answer

Use a compact constructor when you are validating or normalising the record components:

public record Money(long amountMinor, String currency) {
    public Money {
        if (amountMinor < 0) throw new IllegalArgumentException("negative amount");
        Objects.requireNonNull(currency, "currency");
        currency = currency.toUpperCase(Locale.ROOT);
    }
}

The compact constructor has no parameter list. You can reassign the parameters, but you cannot assign this.currency = ...; the compiler writes the field assignments after your constructor body. Every other constructor must start with this(...), so all paths go through the canonical constructor.