Java str.split returning empty elements using RegEx

Question

I want to strip out anything from a string that isn't a plus sign, or a minus, or a multiplication sign or a division sign (/).

So i thought I'd use RegEx and negative lookahead.

Given a Java array:

String[] operandsArray = str.split("(?!\\u002A|\\u002B|\\u002D|\\u002F).")

And a test string of 55+5, the resulting array operandsArray contains:

0:""
1:""
2:"+"

I'm looking for it to contain just the operands, so:

0:"+"

and given: 55+6-6*6/6, would return:

0:"+"
1:"-"
2:"*"
3:"/"

It should also match duplicates as well, so given 5+5+5+5, would return:

0:"+"
1:"+"
2:"+"

Can anyone help with this, thanks

It seems you just want to match and extract with [-+/*] regex. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 3, 2021 at 16:54
@WiktorStribiżew Hi, using [-+/*] will strip out the operands and leave behind anything else, resulting in an array that, say given 55+5, would contain 55 and 5, I'm looking to do the opposite so that only * would remain — WhatTheWhat
– WhatTheWhat, Commented Nov 3, 2021 at 16:58
Remove everything which is not an operator and then split at each char: str.replaceAll("[^-+/*]","").split("") — Eritrean
– Eritrean, Commented Nov 3, 2021 at 17:00
Do not use split, use Matcher#find as I showed in my top comment. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 3, 2021 at 20:53

Ryszard Czech · Accepted Answer · 2021-11-03 22:46:20Z

1

Use

import java.util.*;
import java.util.stream.*;
import java.util.regex.*;

class Test
{
    public static void main (String[] args) throws java.lang.Exception
    {
        String text = "55+6-6*6/6";
        String[] results = Pattern.compile("[+/*-]").matcher(text)
            .results()
            .map(MatchResult::group)
            .toArray(String[]::new);
        System.out.println(Arrays.toString(results)); 
    }
}

See Java proof.

Results: [+, -, *, /]

answered Nov 3, 2021 at 22:46

Ryszard Czech

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