#1 Need an evaluator which would evaluate a string expression like a=b=c=...=n and return a boolean result

[Fathzer]

Hello,

You should probably have a look at the code in creating a simple evaluator from scratch and assuming a, b, ... n are variables, Working with variables.

If you encounter problem, you can post your code there.

Best regards,

Jean-Marc Astesana

[praveen]

I want to define the operator EQUAL like this:
public final static Operator EQUAL = new Operator("=", n, Operator.Associativity.);

The operand count could be anything... i dont want to set a limit. Also the operator would have to equate n number of operands. So what would its associativity be?

[Fathzer]

Javaluator only supports unary and binary operators (n = 1 or 2).
Nevertheless I think there is a solution using Javaluator binary operator.

Please check the following code:

import java.util.HashMap;
import java.util.Iterator;

import net.astesana.javaluator.AbstractEvaluator;
import net.astesana.javaluator.Operator;
import net.astesana.javaluator.Operator.Associativity;
import net.astesana.javaluator.Parameters;

/** This evaluator tests if all the elements of a variable set are equals.
 * <br>The evaluation returns null if one variable is not equals to others.
 */
public class Test extends AbstractEvaluator<String> {
private static final Operator EQUALS = new Operator("=", 2, Associativity.RIGHT, 1);

public Test() {
    super(getParameters());
}

private static Parameters getParameters() {
    Parameters parameters = new Parameters();
    parameters.add(EQUALS);
    return parameters;
}

@Override
protected String toValue(String literal, Object evaluationContext) {
    return literal;
}

@Override
protected String evaluate(Operator operator, Iterator<String> operands, Object evaluationContext) {
    String first = operands.next();
    String second = operands.next();
    if ((first==null) || (second==null)) return null;
    String firstValue = ((HashMap<String, String>)evaluationContext).get(first);
    String secondValue = ((HashMap<String, String>)evaluationContext).get(second);
    return firstValue.equals(secondValue)?first:null;
}

/**
 * @param args
 */
public static void main(String[] args) {
    AbstractEvaluator<String> eval = new Test();
    HashMap<String, String> variables = new HashMap<String, String>();
    variables.put("a", "value");
    variables.put("b", "value");
    variables.put("c", "value");
    variables.put("d", "value");
    variables.put("e", "different value");
    System.out.println (eval.evaluate("a=b=c=d=a", variables));
    System.out.println (eval.evaluate("a=b=e=c", variables));
}
}

Best regards,

Jean-Marc Astesana

[praveen]

Hey Jean,
Thanks a lot for your code. However i need something that would evaluate variables of "Double" type and return a boolean result (true if all operands equal; false if all operands are not equal). Or it could return a string result itself (pass if all operands equal; fail if all operands are not equal). Your inputs would be greatly appreciated. I tried to override toValue() method with boolean return value. Its throwing an error. Im not sure how to do this.

[Fathzer]

Hi,

Here is a new version that works with variables containing any type you want and returning "pass" or "fail".
If you want to return a boolean, you can implement a method that calls super.evaluate, then returns true or false depending on the result (a string or null).

package test;
import java.util.HashMap;
import java.util.Iterator;

import net.astesana.javaluator.AbstractEvaluator;
import net.astesana.javaluator.Operator;
import net.astesana.javaluator.Operator.Associativity;
import net.astesana.javaluator.Parameters;

/** This evaluator tests if all the elements of a variable set are equals.
 * <br>The evaluation returns null if one variable is not equals to others.
 */
public class VariablesEquality extends AbstractEvaluator<String> {
private static final Operator EQUALS = new Operator("=", 2, Associativity.RIGHT, 1);

public VariablesEquality() {
    super(getParameters());
}

private static Parameters getParameters() {
    Parameters parameters = new Parameters();
    parameters.add(EQUALS);
    return parameters;
}

@Override
protected String toValue(String literal, Object evaluationContext) {
    return literal;
}

@Override
protected String evaluate(Operator operator, Iterator<String> operands, Object evaluationContext) {
    String first = operands.next();
    String second = operands.next();
    if ((first==null) || (second==null)) return null;
    Object firstValue = ((HashMap<String, Object>)evaluationContext).get(first);
    Object secondValue = ((HashMap<String, Object>)evaluationContext).get(second);
    return firstValue.equals(secondValue)?first:null;
}

@Override
public String evaluate(String expression, Object evaluationContext) {
    return super.evaluate(expression, evaluationContext)==null ? "fail" : "pass";
}

/**
 * @param args
 */
public static void main(String[] args) {
    AbstractEvaluator<String> eval = new VariablesEquality();
    HashMap<String, Object> variables = new HashMap<String, Object>();
    variables.put("a", Double.valueOf(1));
    variables.put("b", Double.valueOf(1));
    variables.put("c", Double.valueOf(1));
    variables.put("d", Double.valueOf(1));
    variables.put("e", "a string");
    System.out.println (eval.evaluate("a=b=c=d=a", variables));
    System.out.println (eval.evaluate("a=b=e=c", variables));
}
}

Another way would be to implement a function areEquals(a,b,c ...). But it's not your question ;-)

Best regards,

Jean-Marc Astesana