#13 Declare unkwon tokens as variables.

[Pedro Vieira]

Hi,

Suppose I let the user input a expression like sin(x), but x could be anything: variable12, z, randomName, u1, etc.

I want to get that unknown token (variable/constant) from the expression and use it as a key to retrieve a value in a map.

In other words, I want modify your code so, when parsing an expression for tokens, unkown tokens are automatically declared as StaticVariables.

I could not identify an appropriate place in the code to make such modification. Could you give me some ideias?

[Fathzer]

Hi,
Sorry if I didn't understand the question but it seems using StaticVariableSet is what you are looking for.
http://javaluator.sourceforge.net/en/doc/tutorial.php?chapter=variables
It does not require any code modification.
Please let me know if I am wrong.
Best regards,
Jean-Marc Astesana

[Pedro Vieira]

This is what I tried to do: Override the toValue method of DoubleEvaluator as to it search for the literal in a variables map before throwing the Illegal Argument Exception; then setting the variable if found.

package userInteraction;

import java.text.NumberFormat;
import java.text.ParsePosition;
import java.util.HashMap;
import java.util.Locale;

import com.fathzer.soft.javaluator.DoubleEvaluator;
import com.fathzer.soft.javaluator.Parameters;
import com.fathzer.soft.javaluator.StaticVariableSet;

/**
 * An adapted Double evaluator from fathzer's javaluator package.
 * <p>
 * It searches for the literal in a variables map before throwing the 
 * Illegal Argument Exception in the toValue method. 
 */
public class AdaptedEvaluator extends DoubleEvaluator {

    private static final ThreadLocal<NumberFormat> FORMATTER = new ThreadLocal<NumberFormat>() {
          @Override
          protected NumberFormat initialValue() {
            return NumberFormat.getNumberInstance(Locale.US);
          }
    };

    private static StaticVariableSet<Double> variables = new StaticVariableSet<Double>();

    private static HashMap <String, Double> variableMap;

    public static void setMap(HashMap <String, Double> variableMap) {
        AdaptedEvaluator.variableMap = variableMap;
    }

    public AdaptedEvaluator() {
        super();        
    }

    public AdaptedEvaluator(Parameters parameters) {
        super(parameters);      
    }

    @Override
    protected Double toValue(String literal, Object evaluationContext) {

        ParsePosition p = new ParsePosition(0);

        Number result = FORMATTER.get().parse(literal, p);

        if (p.getIndex()==0 || p.getIndex()!=literal.length()) {

            if (variableMap.containsKey(literal)){

                variables.set(literal, variableMap.get(literal));
            }           
            else {
                throw new IllegalArgumentException( literal + 
                        " is not a number, nor a variable in the variable map");
            }

        }

        return result.doubleValue();
    }

}

package userInteraction;

import java.util.HashMap;

public class testing {


    public static void main(String[] args) {

        // Program logic that constructs the variable map.
        HashMap <String, Double> variableMap = new HashMap<String, Double>();

        variableMap.put("h1", 11.2);

        AdaptedEvaluator eval = new AdaptedEvaluator();

        AdaptedEvaluator.setMap(variableMap);


        // get user input and evaluate, without explicit declaration of the variable "h1".  
        String expression = "sin(h1)";

        double result = eval.evaluate(expression);

        System.out.print(result);
    }

}

When I try to run the testing it throws the exception:

Exception in thread "main" java.lang.NullPointerException
at userInteraction.AdaptedEvaluator.toValue(AdaptedEvaluator.java:63)
at com.fathzer.soft.javaluator.DoubleEvaluator.toValue(DoubleEvaluator.java:48)
at com.fathzer.soft.javaluator.AbstractEvaluator.output(AbstractEvaluator.java:133)
at com.fathzer.soft.javaluator.AbstractEvaluator.evaluate(AbstractEvaluator.java:343)
at com.fathzer.soft.javaluator.AbstractEvaluator.evaluate(AbstractEvaluator.java:214)
at userInteraction.testing.main(testing.java:23)

So result.doubleValue() is causing the excpetion but I cannot identify why.

Is it clearer now what I am asking for?

Regards,
Pedro

[Fathzer]

Here is a version of your testing code that works without any subclass. It uses StaticVariableSet:
package userInteraction;

import com.fathzer.soft.javaluator.DoubleEvaluator;
import com.fathzer.soft.javaluator.StaticVariableSet;

public class Testing {

    public static void main(String[] args) {
        // Program logic that constructs the variable map.
//        HashMap <String, Double> variableMap = new HashMap<String, Double>();
//        variableMap.put("h1", 11.2);
//        AdaptedEvaluator eval = new AdaptedEvaluator();
//        AdaptedEvaluator.setMap(variableMap);

        DoubleEvaluator eval = new DoubleEvaluator();
        final StaticVariableSet<Double> variables = new StaticVariableSet<Double>();
        variables.set("h1", 11.2);

        // get user input and evaluate, without explicit declaration of the variable "h1".  
        String expression = "sin(h1)";
//        double result = eval.evaluate(expression);
        double result = eval.evaluate(expression, variables);
        System.out.print(result);
    }
}

Best regards,

Jean-Marc Astesana

[Pedro Vieira]

Sir, you did not understand... (laughs)

In my particular case, I cannot declare the varible in a default way. That is because it would require me to change too many parts in my program. If I can change only one single method, I save myself a lot of work and avoid some bugs.

Anyway, below is what worked for me, in case anyone has a similar need.

/**
 * An adapted Double evaluator from fathzer's javaluator package.
 * <p>
 * It searches for the literal in a variables map before throwing the 
 * Illegal Argument Exception in the toValue method.
 * <p>
 * This way, there is no need to explicitly declare the variable set.
 */
public class AdaptedEvaluator extends DoubleEvaluator {

    private static final ThreadLocal<NumberFormat> FORMATTER = new ThreadLocal<NumberFormat>() {
          @Override
          protected NumberFormat initialValue() {
            return NumberFormat.getNumberInstance(Locale.US);
          }
    };

    private static StaticVariableSet<Double> variables = new StaticVariableSet<Double>();

    private static HashMap <String, Double> variableMap;

    public static void setMap(HashMap <String, Double> variableMap) {
        AdaptedEvaluator.variableMap = variableMap;
    }

    public AdaptedEvaluator() {
        super();        
    }

    public AdaptedEvaluator(Parameters parameters) {
        super(parameters);      
    }

    @Override
    protected Double toValue(String literal, Object evaluationContext) {

        ParsePosition p = new ParsePosition(0);

        Number result = FORMATTER.get().parse(literal, p);

        if (p.getIndex()==0 || p.getIndex()!=literal.length()) {

            if (variableMap.containsKey(literal)){
                // declare variable
                variables.set(literal, variableMap.get(literal));

                literal = variableMap.get(literal).toString();

                result = FORMATTER.get().parse(literal, p);
            }           
            else {
                throw new IllegalArgumentException( literal + 
                        " is not a number, nor a variable in the variable map");
            }

        }

        return result.doubleValue();
    }

}

Many thanks you for your attention,
Pedro