Formatting Quantities: maxFractionDigits are ignored

[einsweniger]

I'm trying to use the Library for formatting numbers up to a specific length in decimal places.
Example given: use 3.0001 and print it with up to 4 or 2 fraction digits, yielding 3.0001 and 3 respectively.

Example:

    val floorAfter4Digits = NumberFormat.getNumberInstance().apply {
      maximumFractionDigits = 4
      roundingMode = RoundingMode.FLOOR
    }
    val floorAfter2Digits = NumberFormat.getNumberInstance().apply {
      maximumFractionDigits = 2
      roundingMode = RoundingMode.FLOOR
    }

Using the same logic, I'd like to format Quantities (outputting "3.0001 N" and "3 N") by re-using the number formatting from above:

    val floorQuantityAfter4Digits = NumberDelimiterQuantityFormat
      .builder()
      .setNumberFormat(floorAfter4Digits) // <-- reusing formatter from above
      .setUnitFormat(SimpleUnitFormat.getInstance())
      .build()
    val floorQuantityAfter2Digits = NumberDelimiterQuantityFormat
      .builder()
      .setNumberFormat(floorAfter2Digits) // <-- reusing formatter from above
      .setUnitFormat(SimpleUnitFormat.getInstance())
      .build()

Now, just formatting numbers yields the correct result, but the Quantities are not formatted correctly:

    val double30001 = 3.0001
    val quantity30001 = Quantities.getQuantity(double30001, Units.NEWTON)
    assertEquals("3.0001", floorAfter4Digits.format(double30001)) // ✅
    assertEquals("3", floorAfter2Digits.format(double30001)) // ✅
    assertEquals("3.0001 N", floorQuantityAfter2Digits.format(quantity30001)) // ✅
    assertEquals("3 N", floorQuantityAfter4Digits.format(quantity30001)) // ❌
    // ^--- org.opentest4j.AssertionFailedError: expected: <3 N> but was: <3.0001 N>

The last test fails, which is unexpected. Am I using this wrong, somehow? Or is this a bug?

[keilw]

Why would 2 fraction digits be formatted 3 and not 3.00?

You use double which usually gets widened to BigDecimal for higher precision.
Did you try passing a BigDecimal that is maybe also adjusted accordingly as for the fractionDigits, etc.?

[einsweniger]

I expected this to deliver the same results as the functions from the JDK. Hence the inclusion of the examples on how other formatting parameters work. If you intended to divert from the JDK, thats fine. It’s just that I guessed, that a reference implementation does work the same ways as the JDK.

[keilw]

It does, but your variables seem to be wrongly applied.

If
assertEquals("3.0001", floorAfter4Digits.format(double30001))
so should
assertEquals("3.0001 N", floorQuantityAfter4Digits.format(quantity30001))

The only issue (although you flagged it as OK in your tests) is, why floorQuantityAfter2Digits formats "3.0001 N" as well.

There was a kind of tweak in NumberDelimiterQuantityFormat to override the maximumFractionDigits, After checking, it had no negative effect on the JUnit tests, I removed that, so from Indriya 2.2.4 you have greater control over the formatting yourself.