How do i convert a string to double in java when the string contains math functions?

Question

i have a string with a math function, like "35+20". i want a new double variable that takes in the result of the math function i.e, 55.0 How do i achieve this? this is actually for android, i'm making a calculator..

You may find the answer here http://stackoverflow.com/questions/3422673/evaluating-a-math-expression-given-in-string-form — Imesha Sudasingha, Jun 05 '16 at 03:20

score 0 · Answer 1 · answered Jun 05 '16 at 03:22

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Manually parse the string and do a calculation at each operator symbol. It will get more complicated when dealing with brackets, however.

answered Jun 05 '16 at 03:22

soundHippo

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score 0 · Answer 2 · edited Jun 20 '20 at 09:12

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If you want to write it yourself, you'll probably want to implement the Shunting Yard Algorithm.

There are also some libraries that handle it for you.

https://github.com/uklimaschewski/EvalEx

edited Jun 20 '20 at 09:12

Community

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answered Jun 05 '16 at 03:28

chessdork

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score 0 · Answer 3 · answered Jun 05 '16 at 03:28

Since you have mentioned you are working on a calculator I am assuming that you might not only be interested in just the + operation but on a bunch of other stuffs too. You can look in to open source GitHub project linked below which provides the JAVA implementation for the stuff you are trying to do https://github.com/uklimaschewski/EvalEx which can give you a good set of functionality that you desire. This project takes in a string as an expression and the returns the result in BigDecimal format. You can always extend it and tweek it to custom suite you needs.

How do i convert a string to double in java when the string contains math functions?

3 Answers3