ISO Standards

ISO-8601 calendar system

The ISO-8601 calendar system, also known as the International Standard Organization (ISO) 8601 Data and time - Representation and exchange, is an international standard for the representation of dates and times. It defines a well-defined, unambiguous way to exchange date and time information across different countries and cultures, avoiding confusion and misinterpretation.

Key characteristics of the ISO-8601 calendar system:

• Basic format: The basic format for representing a date is YYYY-MM-DD, where:

  • YYYY represents the four-digit year (e.g., 2024 for the current year)

  • MM represents the two-digit month (01 for January, 02 for February, etc.)

  • DD represents the two-digit day of the month (01 for the first day, 31 for the last day, etc.)

• Time representation: Time is typically represented in 24-hour format using hours-minutes-seconds notation, separated by colons (e.g., 15:08:23).

• Optional components: The standard allows for optional components like:

  • Milliseconds: Can be added after seconds with a decimal point (e.g., 15:08:23.123).

  • Timezone offset: Can be specified using the Z character for UTC or the plus/minus symbol followed by the offset in hours and minutes (e.g., 2024-03-05T15:08:23+05:30 for a time 5 hours and 30 minutes ahead of UTC).

• Week dates: The standard also defines a format for representing dates based on the week number and day of the week (e.g., 2024-W10-5 for the fifth day of the tenth week in 2024).

• Ordinal dates: Dates can be represented based on the day of the year (e.g., 2024-064 for the 64th day of 2024).

Benefits of using ISO-8601:

• Universality: It's an internationally recognized standard, avoiding confusion and ensuring accurate data exchange across borders.

• Machine-readable: The structured format makes it easy for computers to parse and interpret dates and times.

• Sorting: Dates in ISO-8601 format can be easily sorted chronologically due to their numerical representation.

Examples:

• Date only: 2024-03-05 (today's date)

• Date and time: 2024-03-05T15:08:23 (today's date and time at 3:08 PM)

• Date and time with timezone: 2024-03-05T15:08:23Z (today's date and time in UTC)

• Date and time with offset: 2024-03-05T15:08:23+05:30 (today's date and time 5 hours and 30 minutes ahead of UTC)

ISO-4217 currency codes

ISO 4217 is the international standard for defining currency codes. It was established by the International Organization for Standardization (ISO). Each currency is assigned a three-letter alphabetic code, a three-digit numeric code, and usually a minor unit (i.e., number of decimal places).

ISO 4217 defines:

• Alphabetic Code (e.g., USD, INR, EUR) – Used in programming, APIs, banking systems.

• Numeric Code (e.g., 840 for USD) – Used for processing and data interchange.

• Minor Units – Number of decimal places (e.g., 2 for USD, 0 for JPY).

• Currency is tied to a Locale, so use Currency.getInstance(Locale) when displaying to users.

• Not all currencies have a minor unit (e.g., JPY has 0 fraction digits).

• You cannot create a custom currency using this class. It strictly follows ISO 4217.

List of Common ISO 4217 Currency Codes

Code	Country	Symbol	Numeric	Fraction Digits
USD	United States	$	840	2
INR	India	₹	356	2
EUR	Eurozone	€	978	2
JPY	Japan	¥	392	0
GBP	United Kingdom	£	826	2
AED	UAE	د.إ	784	2

Java provides built-in support for ISO 4217 via the java.util.Currency class.

Method	Description
Currency.getInstance(String currencyCode)	Gets a Currency instance for a given ISO 4217 code like "USD"
Currency.getInstance(Locale locale)	Gets currency by country locale, e.g., Locale.US
getCurrencyCode()	Returns the 3-letter ISO 4217 currency code
getSymbol()	Returns the symbol (like $ or ₹)
getSymbol(Locale locale)	Returns the symbol based on locale
getDefaultFractionDigits()	Returns the minor unit (like 2 for USD, 0 for JPY)
getNumericCode() (Java 19+)	Returns the numeric ISO 4217 code

Example Code

import java.util.Currency;
import java.util.Locale;

public class CurrencyExample {
    public static void main(String[] args) {
        Currency usd = Currency.getInstance("USD");
        System.out.println("Currency Code: " + usd.getCurrencyCode());        // USD
        System.out.println("Currency Symbol: " + usd.getSymbol());            // $
        System.out.println("Default Fraction Digits: " + usd.getDefaultFractionDigits()); // 2

        Currency inr = Currency.getInstance(Locale.forLanguageTag("en-IN"));
        System.out.println("Currency Code: " + inr.getCurrencyCode());        // INR
        System.out.println("Currency Symbol: " + inr.getSymbol());            // ₹
    }
}

Limitations

• Currency.getAvailableCurrencies() returns a static list. It does not update dynamically with latest ISO changes unless the JDK is updated.

• Custom or virtual currencies like BTC (Bitcoin) are not included unless officially added by ISO.