Java: Splitting string equation into numbers and operators

Question

I am trying to split a string equation into two arrays: numbers and operators.

String expr = "3/20.0";

String[] numbers = expr.split("[+-/\\*]");
String[] operators = expr.split("[^+-/\\*]+");

System.out.println(Arrays.toString(numbers));
System.out.println(Arrays.toString(operators));

But my code prints out: [3, 20, 0] [, /, .]

But I'm trying to get [3, 20.0] [, /]

I am not sure why the comma is in front of the operators array, but mainly I just want 20.0 to be one element in the numbers array and keep decimal points out of my operators array.

Answer 1

The comma's are just showing you the element partition.
This [, means the first element is blank.

Try these raw regex

For numbers, split on [^\\d.]+
For operators, split on [\\d.]+

And, I don't know if Java split can delete empty elements, but you'd want to
do a check post process if you can.

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Split Notes -
[\\d.]+ is a class that generally matches numbers, ie. 'dd.dd' ( leaves operators )
[^\\d.]+ is the inverse where it matches operators ( leaves numbers )