Provides the unit system management system as inspired from JSR-275.

Package Specification

The unit package provides a number of notions:

The notion of physical dimension as used in dimensional analysis
The notion of order of magnitude) with its algebra
The notion of unit itself (see also the International system of units)

The Dimension class

The physical magnitudes are organized as a combination of 7 elementary dimensions which are:

The temperature
The duration
The mass
The length
The amount of substance
The electric intensity
The luminous intensity

More concretely, a physical magnitude dimension is represented as the integral powers of these seven elementary dimensions. For example, a force is a mass (power 1) by a distance (power 1) divided by seconds squared (power -2). All the other dimensions have power 0. We can obtain new dimensions by multiplying and dividing dimensions as well as taking their power and root. If the powers are all 0, the dimension is the origin of the physical quantities called ONE. Two dimensions are compatible if they have the same powers for the same elementary dimensions. A dimension contains another if the other powers are inferior or equal to the dimension powers. They are equal if they contain each-other, or equally if they are compatible. In this package, we assume that a unit is non-ambiguously characterized by its dimension. Therefore units are compatible if and only if their dimensions are.

The OrderOfMagnitude class

An order of magnitude is a multiplier to convert between compatible units. They are expressed as powers of 10 and have well defined names in the international standards. The power zero of 10 is called UNIT.

The Unit classes

A unit is an object (called a standard) used as a reference to measure a physical quantity. It may have an associated symbol and can be build from other units by conversion. They are expected to be organized in unit systems. A unit system is defined by a set of base units and a set of units obtained by conversion (the derived units), by multiplication or division (the multiply units) or by cloning (the alternate units). In the international standards, the base units are associated to each of the 7 elementary dimensions but any set of base units can be defined as such. The base unit whose dimension is ONE is called DIMENSIONLESS.

The UnitConverter classes

A unit converter converts back and forth between two units linked by a conversion. The possible conversion are the multiplication/division (including by a rational number for better precision), addition/subtraction and logarithm/exponential.

The exceptions

There are only two possible exceptions: either two units are not compatible (they do not have the same dimension) or they are not convertible (one of the conversions in-between is not linear and, therefore, cannot be reversed). In both cases, the conversion fails.