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Parsing a mathematical expression without spaces

I am trying to use Scanner to parse a string for numbers and operators. It works for me if each token is separated by a space, but if there are no spaces the scanner doesn't seem to work. This example shows my problem:

        final Pattern number_pattern = Pattern.compile("-?(?:\\d+(?:\\.\\d+)?|\\.\\d+)");
        String test1 = "5 + 6";
        String test2 = "5+6";
        Scanner sc1 = new Scanner(test1);
        Scanner sc2 = new Scanner(test2);
        boolean found1 = sc1.hasNext(number_pattern); // true
        boolean found2 = sc2.hasNext(number_pattern); // false

I am looking for an easy way, preferably using something in the Java standard library to parse a string for numbers and operators. I try to avoid examining the string one character at a time.

A string can contain a long expression with many numbers and operators, and I need to extract all of them. So I couldn't replace all operators with a space, for example.

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1 answer


Use a scanner instead of a scanner:



Matcher m = number_pattern.matcher(test2);
while(m.find()) {
    System.out.println(m.group(0));
}
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