I don't think that it is possible to do that with Processing.
You could interpret the String and call a function based on the readings, or if you have a set of a few such statements that you want to execute, you could define constants for those and compare...

But first, I would look at your code and make sure that it is absolutely necessary for you to interpret code at runtime.

Some other posts (yes, there are a couple of this topic) suggest BeanShell... Just thought I'd mention it.

Ok thank you I will find another solution was to run code in a file that was.

If it's in a file, then you might be able to launch a compiler from within the program and then run that-
You would need open(), but that has not worked reliably for me in the past.
There is likely a pure Java alternative.

Often people are asking technical questions on a precise topic that is actually a dead end to their problem...
Explaining precisely what is the real problem can help better, as we can find alternative technical solutions.