How to get semantic quantity names for unit display

[laeubi]

The Problem

We need to display chart axis labels like Time (min), Distance (km), Voltage (mV). This requires two pieces of information per axis: the quantity name (e.g. "Distance") and the unit symbol (e.g. "km").

The API has no runtime-accessible concept of a "quantity name" attached to a Unit. The generic type parameter Quantity<Q> (e.g. Unit<Length>) is erased at runtime, and Unit.getName() returns the unit name (e.g. "Metre"), not the quantity name (e.g. "Length") and sometimes even null:

Unit Expression	Class	getSymbol()	getName()	toString()
Units.METRE	BaseUnit	m	Metre	m
Units.SECOND	BaseUnit	s	Second	s
Units.KILOGRAM	BaseUnit	kg	Kilogram	kg
Units.HERTZ	AlternateUnit	Hz	Hertz	Hz
Units.VOLT	AlternateUnit	V	Volt	V
Units.BECQUEREL	AlternateUnit	Bq	Becquerel	Bq
Units.MINUTE	TransformedUnit	min	Minute	min
Units.HOUR	TransformedUnit	h	Hour	h
Units.CELSIUS	TransformedUnit	℃	Celsius	℃
Units.GRAM	TransformedUnit	null	Gram	g
NANO(METRE)	TransformedUnit	null	null	nm
MILLI(SECOND)	TransformedUnit	null	null	ms
KILO(METRE)	TransformedUnit	null	null	km
KILO(HERTZ)	TransformedUnit	null	null	kHz
MILLI(VOLT)	TransformedUnit	null	null	mV
AbstractUnit.ONE	ProductUnit	``	One	one

• getName() returns null for all metric-prefixed units — the most common ones in scientific applications
• getSymbol() also returns null for prefixed units (only toString() works)
• getName() always returns a unit name ("Metre", "Hertz"), never a quantity name ("Length", "Frequency")
• There's no way to distinguish unit names from quantity names programmatically

The closest options:

Method	Returns	Problem
unit.getName()	Unit name ("Metre", "Hertz")	Not a quantity name; null for prefixed units
unit.getDimension()	Physical dimension [L]	Lossy: Wavelength, Distance, Height all map to [L]
Quantity<Q> type param	Compile-time only	Erased at runtime; can't inspect
unit.isCompatible(X)	Boolean	Requires manual mapping table from dimension→name

While even the last has some shortcomings: HERTZ and BECQUEREL share the same dimension [1/T] but are semantically different quantities (Frequency vs. Radioactivity):

This means dimension-based inference cannot reliably determine the quantity name. An isCompatible() chain checking HERTZ before BECQUEREL (or vice versa) will always pick one and miss the other. The API provides no way to ask "which quantity type is this unit for?"