The Units class extends AbstractSystemOfUnits and provides a set of a set of static constants for the most common units defined by SI/BIPM, see Supported Units .
MetricPrefix is provided for obtaining multiples or submultiples of system units. Method names mirror SI / Metric prefix names but are uppercase like it's common to constants in Java. MetricPrefix is a "hybrid" enum, defining the constant factors as enumeration elements, but doing the actual conversion via matching static method names like CENTI, MEGA, etc.
Examples:
Unit<Length> m = Units.METRE;
Unit<Length> km = MetricPrefix.KILO(Units.METRE);
Unit<Energy> kW = MetricPrefix.KILO(Units.WATT);
Unit instances returned by one of these methods provide type safety through unit parameterization (the and type parameters). This feature was discussed in the Unit Parametrization chapter of the specification.