Develop Reference

Which "default Locale" is which?

With UNIX locales, the breakdown of which means what is relatively well documented.
LC_COLLATE (string collation)
LC_CTYPE (character conversion)
LC_MESSAGES (messages shown in UI)
LC_MONETARY (formatting of monetary values)
LC_NUMERIC (formatting of non-monetary numeric values)
LC_TIME (formatting of date and time values)
LANG (fallback if any of the above are not set)
Java has a different categorisation which doesn't quite match the real world (as usual):
Locale.getDefault()
Locale.getDefault(Locale.Category.DISPLAY)
Locale.getDefault(Locale.Category.FORMAT)
If you read the documentation on these, Locale.getDefault(Locale.Category.DISPLAY) appears to correspond to LC_MESSAGES while Locale.getDefault(Locale.Category.FORMAT) appears to correspond to some combination of LC_MONETARY+LC_NUMERIC+LC_TIME.
There are problems, though.
If you read the JDK source, you start to find many worrying things. For instance, ResourceBundle.getBundle(String) - which is entirely about string messages - uses Locale.getDefault(), not Locale.getDefault(Locale.Category.DISPLAY).
So I guess what I want to know is:
Which of these methods is supposed to be used for which purpose?
Related, but I made a little test program to see which Java locales corresponded to which UNIX locales and got even more surprising results.
import java.util.Locale;
public class Test {
public static void main(String[] args) {
System.out.println(" Unqualified: " + Locale.getDefault());
System.out.println(" Display: " + Locale.getDefault(Locale.Category.DISPLAY));
System.out.println(" Format: " + Locale.getDefault(Locale.Category.FORMAT));
}
}
Locales according to my shell:
$ locale
LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL="en_US.UTF-8"
Output of the program:
$ java Test
Unqualified: en_AU
Display: en_AU
Format: en_AU
So it turns out Java doesn't even get it from the UNIX locale. It must be using some other back door to get the settings without using those.

It's hard to understand what you are asking here. Instead, you make a statement that reveals that you're not necessary a Java programmer. It's OK, it does not matter really.
Few things to clarify:
The Locale class is in JDK since Java 1.1
Things like Locale.Builder, Locale.Category and many others are here from Java 7 (JDK 1.7)
Locale-aware classes and methods like DateFormat, NumberFormat, Collator, ResourceBundle, String.toLowerCase(Locale), String.toUpperCase(Locale) and many, many more are here for quite a long time each (long before JDK 1.7)
Prior to Java 7/JDK 1.7 there was only one method of acquiring current OS Locale - call Locale.getDefault() (that is without parameters)
In other words, prior to Java 7, Java's Locale Model was as simple as one system property composed of a language, a country and an optional locale variant. That has changed with Java 7 (end was further extended with Java 8...) and now you have two system properties, one for formatting and one for displaying user interface messages.
The problem is, there is substantial amount of legacy code written in Java and this could shouldn't break when you upgrade the platform. And that is exactly why you still have parameterless Locale.getDefault() around. Moreover (you may test it yourself), Locale.getDefault() is basically interchangeable with Locale.getDefault(Locale.Category.DISPLAY).
Now, I said formatting and user interface messages. Basically, formatting is not only formatting, but things like character case conversion (LC_CTYPE), collation (LC_COLLATE) as well. Sort of anything but user interface messages. Sort of, because default character encoding (which depends on an OS, BTW) is not part of Locale. Instead you need to call Charset.defaultCharset().
And the fallback rules (built in Java, not read from OS) could be worked out with ResourceBundle.Control class. And as we know, it is rather related to UI category...
The reason why Java Locale Model is different from POSIX (not UNIX, it's more universal), is the simple fact that there are quite a few platforms out there. And these platforms doesn't necessary use POSIX... I mean not only Operating Systems, but things like web... Java is striving to be universal and versatile. As the result Java's Locale Model is convoluted, tough luck.
I have to add that nowadays, it's not only the language and the country, but there are also things like preferred script, calendar system, numbering system, specific collation settings and possibly more. It even works sometimes.

How do I add a new Currency to java.util.Currency for an existing country code in Java 7?

For example, the Chinese currency has the ISO 4217 code CNY. Since free global trading in that currency is restricted though, there's a second 'offshore' currency equivalent, called CNH. Wikipedia has a bit of summary of this all.
In Java 7, there's a method for updating the set of three letter ISO 4217 codes that the JVM ships with. However, it can't be used to add a separate currency code to an existing country code: it would replace CNY with CNH, which is no good for my purposes.
How do I add CNH (which is not in the ISO 4217 list) to the set of available currencies in Java 7, without overwriting CNY?
Put another way, how can I get multiple currency codes for a single country?
Note that this question: How do I add the new currency code to Java? was asked and answered for Java 6. But the strategy of replacing java.util.CurrencyData doesn't work because that file no longer exists.

The key here is in a change that's part of Java 7 to allow updating of the list of currencies without rebuilding rt.jar by replacing a file called currency.data. Using this approach, rather than the currency.properties override approach, allows you to add new Currency codes without affecting other ones from the same country.
What's left unsaid there is how to go about actually building a new currency.data.
This file is generated from a file called CurrencyData.properties, which can be found in the OpenJDK source code in java/util.
What I did was copy the CurrencyData.properties found in the OpenJDK source (openjdk\jdk\src\share\classes\java\util), and changed the line:
BZD084-CAD124-CDF976-CHF756-CLF990-CLP152-CNY156-COP170-CRC188-CSD891-CUP192-\
to
BZD084-CAD124-CDF976-CHF756-CLF990-CLP152-CNH156-CNY156-COP170-CRC188-CSD891-CUP192-\
Then I grabbed the GenerateCurrencyData.java file in the source distribution at openjdk\jdk\make\tools\src\build\tools\generatecurrencydata. This utility takes input from System.In in the same format as CurrencyData.properties, and turns it in to a currency.data file. I made a slight change so that it used a FileInputStream instead of System.In:
currencyData.load(System.in);
to
currencyData.load(new FileInputStream(fileName));
Run that on your edited CurrencyData.properties file and, after putting the original .data file somewhere safe, place the resulting currency.data file in to your JRE\lib directory, and you can now run code that uses Currency.getInstance("CNH").

To the #sharakan answer:
You may also need to add newly changed currency, in my case BYN
BY=BYR;2016-07-01-00-00-00;BYN
in format:
OLD_CUR;DATE_OF_CHANGE;NEW_CUR
Hope it will help someone.

How do I add the new currency code to Java?

The Chinese currency has the ISO 4217 code CNY. Since free global trading in that currency is restricted though, there's a second 'offshore' currency equivalent, called CNH. Wikipedia has a bit of summary of this all.
CNH isn't in ISO 4217, but I'd like to be able to use it in my app without having to write my own Currency class. Presumably there's some kind of list somewhere inside the JVM install. How do I go about adding additional currency codes?
EDIT: See this question for dealing with this in Java 7

Looks like support for this was added with Java 7.
For earlier versions, you could use an equivalent Currency class of your own devising, or less happily, replace the default java.util.Currency class (or java.util.CurrencyData, which contains the raw data) in your classpath (whitepaper).

en_US or en-US, which one should you use? [duplicate]

This question already has answers here:
What is the difference between creating a locale for en-US and en_US?
(4 answers)
Closed 9 years ago.
Assume you want to store the locale of user preference in database, which value you will use?
en_US or en-US
They are two standards, but which one you prefer to use as part of your own application?
Updated: Is seems many web sites use dash instead of underscore, e.g.
http://zh.wikipedia.org/zh-tw
http://www.google.com.hk/search?hl=zh-TW

I'm pretty sure "-" is the standard. If you see "_" somewhere it's probably something some people came up with to make it a valid identifier.
Personally I'd go with "-", just to be correct.
http://en.wikipedia.org/wiki/IETF_language_tag
https://datatracker.ietf.org/doc/html/rfc5646

If you're working with Java, you might as well use the Java locale format (en_US).
The BCP 47 documents actually do specify the en-US format, and it's just as common if not more common than Java-style locale names. But in practice you'll see the form with the underbar quite a bit. For example, both Java and most POSIX-type platforms use the underbar for their language/region separator.
So you can't go far wrong with either choice. But given that you're writing in Java and probably targeting a Unix platform, en_US is probably the way to go.

In Java 7, there is a new method Locale.forLanguageTag(String), which assumes the hyphen as a separator. I'd consider that as normative.
Check the documentation of Locale for more information.

en_US. This is a very useful read.

I don't think en-US is a standard at all for Java. (If you see it somewhere could you add a link).
So just use en_US.

Rounding Half Up with Decimal Format in Android

I want to set the Rounding Mode to HALF_UP on my DecimalFormat, but eclipse is telling me that setRoundingMode() is not available on the DecimalFormat class. My project properties (and the overall Eclipse properties) are using the 1.6 compiler. The developer.android.com site says that I can use either Java 5 or 6 so I'm not sure what the problem is.
import java.math.RoundingMode;
import java.text.DecimalFormat;
completedValueFormatter = NumberFormat.getNumberInstance();
DecimalFormat completedDecimalFormat = (DecimalFormat)completedValueFormatter;
completedDecimalFormat.setRoundingMode(RoundingMode.HALF_UP);
I've also tried using the android tools to generate an ant-based project, tried this code in the project and also got the same compile error. So it doesn't appear to be related to Eclipse. It seems related to the Android API.
Any suggestions?

This doesn't truly answer why I can't use the Java 6 .setRoundingMode(RoundingMode) method in DecimalFormat, but it is at least a work-around.
int numDigitsToShow = this.completedValueFormatter.getMaximumFractionDigits();
BigDecimal bigDecimal = new BigDecimal(valueToBeRounded);
BigDecimal roundedBigDecimal = bigDecimal.setScale(numDigitsToShow, RoundingMode.HALF_UP);
return this.completedValueFormatter.format(roundedBigDecimal.doubleValue());
I create a BigDecimal with the value I need to round, then I get a BigDecimal of that value with the scale set to the number of digits I need to round my values to. Then I pass that rounded value off to my original NumberFormat for conversion to String.
If anyone has a better solution, I'm all ears!

Here is what I suspect the problem is, (assuming I am reading the docs properly) and its a doozy:
According to the java.text.DecimalFormat API documentation, you are not actually getting the Runtime Implimentation of the Java 1.6 RE, but are getting an android "Enhanced Version" that clearly doesn't include the setRoundingMode, which frankly bites.
"This is an enhanced version of DecimalFormat that is based on the standard version in the RI. New or changed functionality is labeled NEW."
A weakness in Java for many many many years has been the DecimalFormat class defaulted to HALF_ROUND_UP and had no way to change that, until JVM 1.6. Pity to see Android is keeping this need to kludge alive.
So looks like we are stuck Kludging BigDecimal scale Settings to format output all over any app that needs it, instead of simply being able to rely on a formatter call alone to get the job done. Not the end of the world, but very disappointing Google.
Of course that same doc says that setRondingMode() works, so perhaps this is a all out BUG??

I guess this would be the best option
http://download.oracle.com/javase/1.4.2/docs/api/java/lang/Math.html#ceil(double)