Adding features

Question

I wanted to extend the code by alpha5and5 for performing a calculation for a string.
I want to extend the limit of code, i.e I want the code to be able to calculate strings having functions like "e"(exponential), "PI"(pi=3.14), "Log"(simple log not "Ln")
I had a hard time adding those and result in nothing.
Here is the original code:
https://code.sololearn.com/cf40iiEcoj4T#java

Answer 1

Does someone want to help??