In Jep 3.5 all error messages are externalized using the standard Java Internationalization mechanism. See Java Trail: Internationalization for of an overview.

The default messages are contained in the com/singularsys/jep/messages.properties file which can be customised. A copy of this file can be found here: messages.properties.

Custom messages file

A localized version of the messages file can be specified for a given language and country A typical copy of the properties file might be

FunctionRequiresNArgumentsFoundN=Fonction «%s» nécessite %d arguments, a trouvé %d.
functions.IllegalParameterException.UnknownFunction=Fonction inconnue
functions.IllegalParameterException.IllegalArgument=: argument illégal:
functions.IllegalParameterException.IllegalArguments=: arguments illégal: 
functions.IllegalParameterException.Expected=\ attendus %s
functions.IllegalParameterException.ExpectedMsg=\ attendus %s
functions.IllegalParameterException.ActualValueClass=\ %s[%s]
functions.IllegalParameterException.ArgumentNumber=,\ numéro %d argument.

The first line gives the message printed when a function is specified with the wrong number of arguments, say sin(1,2). This message is a format string used by String.format(spec,args...). The second example is a more complex message with multiple parts used when an illegal argument is passed to a function or operator. Not all messages needs to be supplied, some are extremely rare.

For the system to find the file it must be in the class path in the com/singularsys/jep directory and named messages_(language)_(Country).properties for example com/singularsys/jep/messages_fr_CA.properties would specify the messages for French (fr) Canadian (CA) locale.

Setting the default Locale

The default locale is normally set by the system. This can be overridden by specifying the user.language and user.country properties on the command line

java -Duser.language=fr -Duser.country=CA com.singularsys.jepexamples.consoles.Console

on unix machines it may be possible to set the default locale by setting the environment variable, LANG, LC_ALL or LC_MESSAGES.

  bash % export LC_ALL=de_DE

The default locale can also be set within java using


this should be called before any Jep code is loaded.

Testing messages

The com.singularsys.jeptests.system.MessagesTest class is a JUnit test class which tests and displays all messages printed by the system. You can use this class to check the results of any custom localization messages.

Standard Error reporting methods

The PostfixMathCommand the base class for custom functions provides a number of methods for checking the types of arguments. For example double asDouble(int position, Object value) checks that the value can be converted to a double. If not a standard error message is generated using the position argument and an IllegalParameterException thrown with this message. For example this method is used in the Signum if it is supplied with a illegal argument, say signum("abc") then the message

signum: illegal argument: abc[String] expected Number, argument number 0.

is generated using the functions.IllegalParameterException.IllegalArgument, functions.IllegalParameterException.ActualValueClass, functions.IllegalParameterException.Expected and functions.IllegalParameterException.ArgumentNumber messages. Other conversion methods include asString(pos,str), asInt(pos,val), asLong(pos,val), asBool(pos,val), and asStrictInt(pos,val). The final method not only checks if the number can be converted to an integer it also check that no rounding occurs.

The IllegalParameterException class offers a number of different constructors for easy generation of standard error messages. If you want your own error message use the parent class EvaluationException.