为什么在 Java 中尝试拆分字符串时出现空字符串？ 以及如何解决？

Question

I am trying to split a string like this:

stringNumbers = "12.34+345.56+45-87.90*43.00";
String[] Operators = stringNumbers.split("[0-9.]");

in the console when I print operators I am getting this:

[, , , , , +, , , , , , +, , -, , , , , *]

The null characters are not my desired output. Why am I getting null charachters and how to solve the problem?

Answer 1

It's because you're splitting by a single character, you would have to do this eagerly:

String[] Operators = stringNumbers.split("[0-9.]*");

Or you can filter the results:

String[] Operators = Arrays.stream(stringNumbers.split("[0-9.]"))
    .filter(str -> !str.equals(""))
    .toArray(String[]::new);

Answer 2

Another option would be to just collect those numbers, with a simple expression such as:

\\d+(?:\\.\\d+)?

Test

import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class RegularExpression{

    public static void main(String[] args){

        final String regex = "\\d+(?:\\.\\d+)?";
        final String string = "12.34+345.56+45-87.90*43.00\n"
             + "12+345+45.8-87*43";

        final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
        final Matcher matcher = pattern.matcher(string);

        while (matcher.find()) {
            System.out.println("Full match: " + matcher.group(0));
            for (int i = 1; i <= matcher.groupCount(); i++) {
                System.out.println("Group " + i + ": " + matcher.group(i));
            }
        }

    }
}

Output

Full match: 12.34
Full match: 345.56
Full match: 45
Full match: 87.90
Full match: 43.00
Full match: 12
Full match: 345
Full match: 45.8
Full match: 87
Full match: 43

---

If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com . If you'd like, you can also watch in this link , how it would match against some sample inputs.

---

RegEx Circuit

jex.im visualizes regular expressions:

Answer 3

String stringNumbers = "12.34+345.56+45-87.90*43.00"; String[] Operators = Arrays.stream(stringNumbers.split("[0-9.]+")) .filter(str -> !str.equals("")) .toArray(String[]::new);