Maintenance Lead Werner Keil will present JSR 354 (Money and Currency). He will discuss the API from a developer as well as user perspective and share details on the design decisions behind the JSR. Monetary values are a key feature of many applications, yet the JDK provides little or no support. The existing java.util.Currency class is strictly a structure used for representing current ISO-4217 currencies, but not associated values or custom currencies. The JDK also provides no support for monetary arithmetic or currency conversion, nor for a standard value type to represent a monetary amount. The session will demonstrate how the JSR models monetary capabilities, monetary amounts, currencies, rounding, financial arithmetics as well as formatting and currency conversion in a platform independent and flexible manner. The first part of the talk will focus on key concepts, improvements like Java 9/Jigsaw modularity and planned new features for a future release followed by a live coding session demonstrating the Money JSR in action.

1. Money, Money, Money,
can be funny
with JSR 354
Werner Keil
@wernerkeil
@jsr354
November 4, 2019

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Who am I?
Werner Keil
• Consultant – Coach
• Creative Cosmopolitan
• Open Source Evangelist
• Software Architect
• Maintenance Lead – JSR 354
• Maintenance Lead – JSR 385
[www.linkedin.com/in/catmedia]
Twitter @wernerkeil

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Agenda
1. History and Motivation
2. Overview
3. Currencies and Amounts
4. Precision, Rounding and Conversion
5. Action
6. Roadmap

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History and Motivation

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Motivation
Monetary values are a key feature to many applications
Existing java.util.Currency class is strictly a structure used for
representing ISO-4217 standard currencies.
No standard value type to represent a monetary amount
No support for currency arithmetic or conversion
JDK Formatting features lack flexibility
<dependency>
<groupId>org.javamoney</groupId>
<artifactId>moneta</artifactId>
<version>1.3</version>
</dependency>

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Overview of JSR 354
Core API: javax.money
CurrencyUnit, MonetaryAmount and exceptions
Conversion API: javax.money.convert
ExchangeRate, ConversionContext, CurrencyConversion
Formatting: javax.money.format
AmountFormatContext, MonetaryAmountFormat
Extensions: javax.money.spi
CurrencyProvider, RoundingProvider, ServiceProvider,…
Reference Implementation: org.javamoney.moneta
TCK: org.javamoney.tck

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Currencies and Amounts
javax.money

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Currencies
ISO 4217
Special Codes
Ambiguities
Unmodeled
Aspects
Minor units
• Precious Metals (XAU, XAG)
• Testing (XTS)
• No Currency (XXX)
• Supranational currencies, e.g. East Caribbean dollar,
the CFP franc, the CFA franc.
• CFA franc: West African CFA franc und Central African CFA
franc = denotes 2 effectively interchangeable (!).
• Switzerland: CHF, CHE (WIR-EURO), CHW (WIR)
• USA: USD, USN (next day), USS (same day)
Legal acceptance, e.g. Indian Rupees are legally accepted in
Bhutan/Nepal, but not vice versa!
Typically 1/100, rarely 1/1000, but also 1/5
(Mauritania, Madagascar), 0.00000001 (Bitcoin)

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Video Game Currencies (Gold, Gil, Rupees, Credits, Gold Rings, Hearts, Zenny,
Potch, Munny, Nuyen…)
Facebook Libra, a new virtual currency you can use to buy
virtual goods in any games or apps of the Facebook
platform that accept payments. Facebook also
plans to use Libra for money transfer similar to
Western Union, MoneyGram or others.
Scrutiny by regulators and some countries
like China may not allow it at all
Bitcoin (sign: BTC) is a decentralized digital currency
based on an open-source, peer-to-peer internet protocol.
It was introduced by a pseudonymous developer named
Satoshi Nakamoto in 2009. Hundreds of “Altcoins” followed
Virtual Currencies

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Local Currencies
Brixton, Bristol Pound,...

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Precision and Rounding
javax.money

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Numeric Precision
• Internal Precision (implied by internal number type)
• External Precision (Rounding applied, when the numeric part is
accessed/passed outside)
• Formatting Precision (Rounding for display and output)
• Interoperability
• Different precision/scale
• Distinct numeric representation
• Serialization
-> only internal rounding is applied automatically.
-> The precision/scale capabilities of an MonetaryAmount are inherited
to its operational results.

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Rounding
• External Rounding and Formatting Rounding depends on use case
• Rounding is modeled as a MonetaryOperator
Example for non standard-rounding: Argentina
• If the third digit is 2 or less,
change it to 0 or drop it.
• If the third digit is between 3
and 7, change it to 5.
• If the third digit is 8 or more, add
one to the second digit and drop the third digit
or change it to 0.
Original Rounded Remark
123.452 123.45 3. digit <3 -> round down
123.456 123.455 3<= 3. digit <=7 -> change to 5
123.459 123.46 3. digit >=8 -> round up
Implementation:
MoneyRounding

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Currency Conversion
javax.money.convert

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Adopters

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Action
@wernerkeil

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Roadmap
• Embracing Java 8 features
• Further support of JSR 310 (Date & Time) types
• Type Annotations (if appropriate)
• Use of Lambdas where appropriate
• Alignment with Java 9+ features
• Modular environment - While the API should be backward-compatible with at least Java SE 8, both
API and RI expose Java 9 modules
• Multi-release JAR files - This should allow a single API and RI to support Java 8, 9 and beyond.
• Bean Validation Support
• Valhalla Inline Types when available
• See https://github.com/JavaMoney/jsr354-api/issues

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Links
JavaMoney: http://javamoney.org
JSR 354 Twitter Account: @jsr354
JSR detail page on JCP.org: https://www.jcp.org/en/jsr/detail?id=354
JavaMoney on GitHub: https://github.com/JavaMoney
JavaMoney on Groups.io: https://javamoney.groups.io

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We’re running for an Associate Seat!

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@wernerkeil