Java String and Mathematical Expression Evaluators

Question

We use the Jeks parser at present to evaluate expressions. I cannot see a way to evaluate string expressions with it - for example:

IF( "Test 1" = "Test 2")

Is there anything out there that can evaluate string and mathematical expressions in Java? Preferably free or open source.

Upper

That's not remotely syntactically correct Java code. Is that intentional? – Stull

I guess it is. He's looking for a Java-Evaluator for a Non-Java-Language (string and mathematical expressions). – Fructuous

Take a look at JEKS: eteks.com/jeks/en – Fructuous

We use Jeks... But I cannot see how you can evaluate IF("Test 1" = "Test 2") – Upper

Answer 1

The answer was a posting on the Jeks forum. I got an answer from Manu. I thought it was not active especially as I could not register on it - but that got sorted.

But if anyone has the same problem then the following lines of code will get it working:

ExpressionParser parser; // we did have = new ExpressionParser(new JeksExpressionSyntax(), null);
JeksInterpreter interpreter; // 

And to create the interpreter:

interpreter = new JeksInterpreter() {

      @Override
      public Object getBinaryOperatorValue (Object binaryOperatorKey, Object param1, Object param2)
      {
        // Only functions may take a cell set as parameter
        if ( param1 instanceof JeksCellSet || param2 instanceof JeksCellSet)
          throw new IllegalArgumentException ();
        // Enabled comparison between any type supported by Jeks
        else if (binaryOperatorKey.equals (JeksExpressionSyntax.OPERATOR_EQUAL))
          return param1 != null && param1.equals (param2)
                   ? Boolean.TRUE : Boolean.FALSE;
        // Enabled comparison between any type supported by Jeks
        else if (binaryOperatorKey.equals (JeksExpressionSyntax.OPERATOR_DIFFERENT))
          return param1 != null && param1.equals (param2) ? Boolean.FALSE : Boolean.TRUE;
        else
          return super.getBinaryOperatorValue (binaryOperatorKey, param1, param2);
      }
    };

    parser = new ExpressionParser(new JeksExpressionSyntax(), null);

Upper

Answer 2

There are a lot of tools out there to evaluate expressions; the correct answer will depend on your exact goals.

Two things that I'd look at:

• Commons EL, which evaluates JSP 2.0 expression language.
• Rhino, which evaluates JavaScript (I think this is part of JDK 1.6, but haven't used it as such).

Halation