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The valueOf methods return objects, the parseXXX methods return primitives.

When you parse: x + y
you get the three parts of the expression.
Sorry, I'm confused about where your problem is. If you have split the expression into its three parts, then you can evaluate it...

Do a Search on the forum for code samples. Or use Google.

There are several ways to do it. I have only used a couple and probably not the easiest ones to use.
The easiest way would be if there were spaces delimiting each of the three parts, then you could...

If your expressions are only 2 operands and an operator, then you should be able to parse the three parts of the expression and evaluate it. If the expression is more complicated, You need to...