How can I split a string for mathematical use in Java?

Question

I asked a similar question recently, but I need some more help.

The user will be able to enter a string, for example:

"-5-1/-2"

It needs to: delimit by +,-,*,/,(,) and negative numbers should be kept together, in this case -5 and -2 should stay together.

This is what I currently have:

String userStrWithoutSpaces=userStr.replaceAll(" ", ""); String[] tokens = userStrWithoutSpaces.split("(?<=[\\-+*/=()])|(?=[()\\-+*/=])");

Which works besides keeping negative numbers together.

Thanks in advance.

You're on the right track , so keep that up . Although if you need a quick-fix , parsers!! — Caffeinated
– Caffeinated, Commented Jan 7, 2013 at 23:48
Be aware that most parsers (I believe) for arithmetic expressions consider that minus as a unary operator, rather than as part of the number; normally, it makes things more consistent and easy. — leonbloy
– leonbloy, Commented Jan 7, 2013 at 23:54
If you want to parse mathematical expressions like this, the right way to do it is with the shunting yard algorithm. It's surprisingly difficult to do with ordinary kinds of parsers. — Tom Anderson
– Tom Anderson, Commented Jan 8, 2013 at 0:00

Bohemian · Accepted Answer · 2013-01-07 23:49:17Z

Try this:

String[] tokens = userStrWithoutSpaces.split( "(?<=[+*/=()])|((?<=-)(?!\\d))|(?=[()\\-+*/=])");

This uses a lookahead to not split when hyphen is followed by digit

Adam Stelmaszczyk · Accepted Answer · 2013-01-07 23:53:21Z

I would use JFlex. You need a lexical analyzer, a piece of code, which will give you tokens from some input text. JFlex is a generator of lexical analyzers. Very fast and reliable analyzers. You specify only a rules, in a form similiar to regular expressions, very convenient. All the low-level job does JFlex. The picture presents idea of JFlex:

enter image description here

Community · Accepted Answer · 2017-05-23 11:48:59Z

Get the result of the arithmetic expression in Java:

How to parse a mathematical expression given as a string and return a number?

Parse it into its number and operator components in java:

Splitting a simple maths expression with regex

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