Quick and Dirty Calculator - Can It Be Done?

Question

I'm making a calculator. I've looked into my options, stacks, postfix, or just using someone else's class. But one idea struck me as more interesting than the others, but while I've programmed plenty, I by no means consider myself a veteran, and I need a little help from you guys and gals.
Is there any way to use Java's own expression evaluator in making a calculator?
I imagine this would be possible by creating a new File by the name of TemporaryClass.java, and having the program write the expression in class form in TemporaryClass.java, for example...
class TemporaryClass
   public TemporaryClass(){
      double x = /* Program writes expression here */ ;
      /* Something class writes x to xValue.dat */
}... and then I would have my main program read in the number printed in xValue.dat, and then it's all Double.parseDouble() from there.
But that's too much of a pain. Is there any simpler way to have java do the work for me, without forcing me to dissect an expression myself?
Thanks in advance,
Scott

Answer 1

i wrote a program similar to this once
you would give it a mathematical expresion in the form of a String (i.e. "3 + 4 * 3") and it would give you an answer
i couldn't find a way to do it so i had to write my own program that would break apart the string and convert it into a mathematical expresion. i did this by using the order of operations (parenthesis, ^, *and/, +and-). i would search for each of the operators in the string using the indexOf(char) method. when i found the appropriate operator i would find the two numbers that were on either side of it, and convert them into doubles using the Double.parseDouble(String method) i would than apply the operator to the two numbers and reconstruct the string with the appropriate answer. i would repeat this using all of the operators until there were no more operators left and than i would call Double.parseDouble(String) one last time to give me a final double answer.