Example: Passing Parameters to an Expression

This example shows how xmlmath expressions can take input parameters, prior to being evaluated, using the family of <input> tags.

To run this example, pass two string parameters to the evaluator:

$ java -jar dist/xmlmath-1.1-SNAPSHOT.jar foo bar < samples/parameters.xml
parameter x: foo
parameter y: bar
$
			

Omitting the parameters will cause warnings to be printed to stderr. Parameter "x" will use its default value:

$ java -jar dist/xmlmath-1.1-SNAPSHOT.jar < samples/parameters.xml
Warning: no value specified for input parameter "x".
Warning: no value specified for input parameter "y".
parameter x: default value
parameter y: null
$
			

							
<expression xmlns="http://xmlmath.org/1.0">

  <inputString name="x" description="Some input parameter" value="default value"/>
  <inputString name="y"/>

  <strcat>
    <string value="parameter x: "/>
    <linkString name="x"/>
    <string value="&#xA;parameter y: "/>
    <linkString name="y"/>
  </strcat>
</expression>
						

Input parameters can be read using the <link> tags. This example uses tag <linkString>, which extends <link>. It is used to link to strings only. For each datatype there is a corresponding link-tag. Apart from <linkString> these include: <linkBoolean>, <linkLong>, <linkDouble> and <linkList>.

Input tags can be used only as the first elements in the <expression> root-tag. Their values can be read anywhere in the expression using <link> tags.