Design Patterns Java™ Workbook

Chapter 3. Adapter

Figure 3.3. Oozinoz models units as instances of the Measure class, whose

subclasses represent particular physical dimensions.

A unit is a standard measure—a standard magnitude of a given dimension. For
example, a cubic inch is a unit of volume, and a pound is a unit of force.
The UnitConstants interface supplies units, and the Measurehierarchy supplies
dimensions for type checking. For example, the UnitConstants interface
supplies a CUBIC_INCH constant whose type is Volume.

You can construct new instances of Measureby building from the units available
in the UnitConstants interface. For example, suppose that the cross section of
a rocket is 0.75 square inches.

Area a = (Area) INCH.times(INCH).times(.75);

The times() method instantiates whichever subclass of Measure reflects the
dimension of the new unit. The return type of this method is Measure, but you can
cast the result to the more specific class that represents the measure's dimension.

To convert a measure to a quantity of a specific unit, divide the measure by the unit.
For example:

package com.oozinoz.units;
public class ShowConversion implements UnitConstants
{
public static void main(String[] args)
{
Volume v = (Volume) QUART.times(3);
showVolume(v);
}