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Units

DOI Maven Central

Units is a Java library designed to handle units and constants. It is designed to handle string based units as well as sharper defined units. Some of the supported features include:

  • conversions of values, e.g.:

    Units.convert(3, "m", "mm");
Units.convert(3, SiBaseUnit.METER, Unit.of("mm"));

    would both return 3000.

  • simplification of string based units, e.g.:

    Units.simplify("kg^3 m^4 s^-6 A^-1");

    would return "J^2 T".

  • finding the names of a unit in a specific context, e.g.:

    Units.inContext("lx s", UnitContextMatch.COMPATIBLE, PhysicsContext.PHOTOMETRY)

    would return a navigable set containing ("luminous exposure").

  • supports SI units, binary units, imperial units, US customary units, atomic units, planck units and many more. The user can also easily define own units.

  • fully supports arbitrary logarithmic units, e.g.

    LevelUnit.BEL.inReferenceTo(1, Unit.of("mV")); // automatically determines ref type -> root power
LevelUnit.BEL.inReferenceTo(1, Unit.of("W"), LevelUnitReferenceType.POWER); // specify type explicitly
Unit.of("ln(re 1 nA)") == LevelUnit.NEPER.inReferenceTo(1, Unit.of("nA")); // true

  • supports SI prefixes, binary prefixes and allows the user to easily implement own prefixes

  • Can handle unknown units if not relevant, e.g.:

    Units.convert(3, "m^2 this_is_not_a_unit", "mm^2 this_is_not_a_unit");

    would return 3e6, as the unknown unit this_is_not_a_unit is the same on both sides of the conversion.

  • for performance critical parts of the code one can obtain the conversion factor (if the conversion is purely multiplicative), e.g.:

    Units.factor("kg", "t");

    will return 1e-3.

  • Allows to check for convertibility

    Units.convertible("s", "min");

    will return true.

  • tightly integrated in the coordinates library

The constants are implemented via a Constant interface that supports e.g.:

  • definition of own constants, e.g.

    // (3 ± 0.2) mole
Constant.of(3, 0.2, "mole");

  • chaining commands, e.g.

    // constant with the distance traveled by light in vacuum in (2 ± 0) seconds as value
PhysicsConstant.SPEED_OF_LIGHT_IN_VACUUM.mul(2, 0, SiBaseUnit.SECOND);

// constant of the elementary charge per (electron) mass
PhysicsConstant.ELEMENTARY_CHARGE.div(PhysicsConstant.ELECTRON_MASS);

Constant c = Constant.of(3, 0.2, "mole");
PhysicsConstant.SHIELDING_DIFFERENCE_OF_T_AND_P_IN_HT.mul(c);

  • (simple) uncertainty propagation

  • the Constant interface provides default implementations for the Texable interface from the jatex module, such that a constant can easily return proper LaTeX code.

  • properly documented implementations for most of the physics constants as defined by NIST, as well as some mathematical constants.

Installation

The artifact can be found at maven central:

<dependency>
    <groupId>eu.hoefel</groupId>
    <artifactId>units</artifactId>
    <version>4.1.1</version>
</dependency>

Requirements

Units is designed to work with Java 17+.