Evaluate basic arithmatic in a string

From: David Morris (dmorris_at_dynamicquest.com)
Date: 04/02/04

Date: Fri, 02 Apr 2004 09:31:30 -0500

OK, this is for you experienced Java programmers out there.

I have a string that contains the following value:

"myValue += 5"

I need, in Java, to be able to evaluate this expression.

myValue can be int, float, long, double, or short.

Likewise, the 5 could also be a variable of any of the above listed
types. ie, "myValue += myValue2".

Just so you know the environment, I an writing a java scripting janguage
where I can have a user build a template on the fly and I interpret all
the java code manually. I am about 75% finished mimicing the JVM in the
  scripting but am lacking basic math functions.

I use a class

class ObjDef {
        Object value;
        Class className;

to store and pass values throughout the script interpretation process.

so I know the value and class of myValue and myValue2 and I know to cast
5 to an int if not otherwise set.

The real caviot comes in that if myValue is an int, the className in
ObjDef is int but the Object is Integer.

How do I get myValue ( which is really ObjDef.value ) to an int so I can
do an actully myValue = myValue + 5 and put it back in the ObjDef class?

Realize if I do a hard cast, 25 different possible combinations (5^2),
so I am looking for a different answer.

Thank you for any help you can offer.