JSR363 - Devoxx US

@leomrlima & @otaviojava & @UnitAPI#JSR363JavaOne
The First IoT JSR: Units of Measurement
JSR-363 [TBW-1406]
Leonardo Lima & Otávio Santana
@leomrlima & @otaviojava & @UnitAPI
https://www.jcp.org/en/jsr/detail?id=363
http://unitsofmeasurement.github.io

Leonardo Lima
•Computer engineer, server & embedded SW developer
•From São Paulo, Brasil, now in Austin, TX
•CTO at
•Spec Lead – JSR363 – Units of Measurement
•V2COM’s Representative at JCP Executive Committee
[www.linkedin.com/in/leomrlima]

Otávio Santana
•Software engineer, Tomitribe
•From Salvador, Brazil
•Java Champion, SouJava JUG Leader
•Apache and OpenJDK Committer
•JSR 363 Expert Group member
•Representative at JCP EC for SouJava
[about.me/otaviojava]

What are Units of Measurement?
10,363 ??????
A Measurement
A Unit
San Jose
São Paulo

What is the problem, in code?
int distance = 10_363; //in ???
float speed = airplane.getSpeed(); //in ???
System.out.println(“TTD: “ + (distance/speed) + “
hours”);
10,363 ??????
A Measurement
A Unit

@YourTwitterHandle#DVXFR14{session hashtag} @leomrlima & @otaviojava & @wernerkeil#JSR363JavaOne
LEARNING FROM THE PAST…
Some examples of how things can go wrong…

Some real-life mishaps…
NASA “Star Wars” Initiative, 1985
Sea Level

2001: Escape of the 250Kg tortoise
Los Angeles Zoo lent Clarence, a 250-kilogram, 75-
year-old Galapagos tortoise, to the Exotic Animal
Training and Management Program at Moorpark
College in Moorpark CA.
The first night in his new home, Clarence wrecked it:
“He just pushed one of the fence poles right
over,” said Moorpark's Chuck Brinkman.
The L.A. Zoo warned that Clarence was big, and
needed an enclosure for an animal that “weighs
in at about 250”, so that's what the college
built.
Unfortunately, they thought the zoo meant 250
pounds, so the enclosure wasn't adequate for
holding a 250-kilogram (552 lbs) beast.
Clarence

Why do we need a specification?
There are no specifications or standards for handling units in Java.
The current solution is to use primitives, that don’t provide any Type
Safety.
The errors are difficult to find using unit testing:
Interface and Internationalization (e.g. radian/degree, meters/feet);
Arithmetic operations (e.g. overflow);
Conversion between units (e.g. from same domain);

What is JSR-363?
Interfaces and abstract classes supporting unit operations including:
Checking of unit compatibility;
Expression of measurement in various units; and
Arithmetic operations on units.
Concrete classes implementing standard unit types (base, derived)
and unit conversion.

CORE THEORY AND CONCEPTS
Some Basic Science behind the API

What is a Unit?
c. (a) Any determinate quantity, dimension, or magnitude adopted as a
basis or standard of measurement for other quantities of the same
kind and in terms of which their magnitude is calculated or
expressed.
Oxford English Dictionary
Or … A well defined standard we all know?
Unit Definition
Second The duration of 9,192,631,770 periods of the radiation corresponding to the
transition between the two hyperfine levels of the ground state of caesium 133
atom
Kilogram The mass of the international prototype kilogram [a very special lump of metal]
metre The distance travelled by light in a vacuum in
3.3356409519815204957557671447492e-9 seconds

A Standard Measurement …
“The nice thing about standards is that you have so many to choose
from.”
Andrew S. Tanenbaum,
Computer Networks 2nd ed., p. 254
Foot
Mile
Yard Chain
Fathom
Furlong
InchNautical Mile
Statute Mile
astronomical unit (AU)
Light year
Parsec(or meter)
Passus (roman)
Hand
ångström
Scots/Welsh/English Mile
Metre fermi micron
Thou (or mil)League
rod/perch/pole
nail
Barleycorn
link
ell Cubitfinger
palm
Poppyseed
Milli Centi Kilo

Dimension
Allows analysis of a quantity by the rational powers of the 7
fundamental dimensions (quantities are compatible when they have
the same dimensions):
length (L), mass (M), time (T), electric charge (I), absolute
temperature (Θ), amount of substance (N) and luminous intensity (J)
Examples:
Speed = length/time - it’s dimensions are L=1,T=-1 (rest 0) (e.g. metre/second - ms-1)
Acceleration is speed/time (m/s/s or ms-2) L=1, T=-2
Force is mass x acceleration M x ((length/time)/time) or M=1, L=1, T=-2
Molar Entropy: M=1 L=2 T=−2 Θ=−1 N=−1 (trust me!)

Quantity
A physical attribute of a thing. Something that can be measured and
has units. Compatible quantities have the same dimension…
Examples:
• Time
• Length
• Speed
• Amount of Substance
• Luminous Intensity
• Volume
• Mass
• Force
• Power
• Electrical Current
• Magnetic Flux Density
• Volumetric Flow Rate
• Fuel Economy*
• Percentage
• Eggs per carton
• Sheep per hour
• Bits and bytes …
… ∞

What is JSR-363, in code?
Airplane airplane = new Airplane(“A380”);
QuantityFactory<Length> lengthFactory =
provider.getQuantityFactory(Length.class);
Quantity<Length> distance = lengthFactory.create(10_363,
KILO(METRE));
Quantity<Speed> airplaneSpeed = airplane.getSpeed();
Quantity<Time> timeToDest = distance.divide(airplaneSpeed)
.asType(Time.class);
System.out.println(“TTD: “ + timeToDest.to(HOUR));
TTD: 11.033853606779548 h

JSR-363 in IoT
IoT is all about measurements (and timestamps and sensor ID). Before
JSR-363, we’d code against primitives: Double, Float, BigDecimal.
With JSR-363, you can make your API typesafe and avoid bugs due to
lack of consistency or misundertandings.

JSR-363 in IoT
Before:
After:
public class ThermometerReading extends Measurement {
private Float temperature;
}
public class ThermometerReading extends Measurement {
private Quantity<Temperature> temperature;
}

Who is going to use JSR-363?
Java developers who work with physical quantities need to handle
measurements in their programs.
Inadequate models of physical measurements can lead to significant
programmatic errors.
Platform providers and developers can provide and use a better
defined API
Embedded developers can have less error-prone, more self-
documented code

JSR-363 timeline
March 11, 2014: Submitted
April 7, 2014: Creation approved
Dec 2014 – Jan 2015: Early Draft (approved)
Nov 2015 – Jan 2016: Public Review (approved)
Q3/2016 : Final Draft
Q3/2016: Final Release

Links to JSR-363
Public mailing list(s) and/or forum(s)
Units-Dev on Google Groups
Units-Users on Google Groups
The JSR page on JCP.org…
And two other “JSR project websites”:
Main project website is on GitHub (unitsofmeasurement)
Java.net site is used for JIRA (deprecated, use GitHub!)
And you can get sample code at our GitHub.

JSR363 - Devoxx US

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