How to allow only specific letters, numbers and symbols in input string

Question

Hi all
i'm new to java and trying to program a polynom calculator.
so, you can enter a polynom string like for example "2.1x^3 + 3x^2 - 1". this all works fine.
but i only need numbers, some special symbols and only the letter x which will be the variable you can enter here, otherwise a message should be displayed that i entered an invalid character or symbol. and is it also possible to check that there is a space before and after a + or - sing?
the input string i'm reading it in with: String inputString = TastaturRead.readString();
anyone out there who can help me?
many thanks in advance.

Answer 1

Please don't cross-post.
Again, this looks backwards here. You seem to be using the string you want to split as the regex string, but again, I'm no expert here.
import java.util.regex.*;
public class Splitter {
    public static void main(String[] args) throws Exception {
        // Create a pattern to match breaks
        String pattern = "[+|-]+";
        Pattern p = Pattern.compile(pattern);
        // Split input with the pattern
        String input = "-5x^3+8x^2 - 2";
        //This smells wrong to me, backwards
        String[] result = p.split(input);
        for (int i=0; i<result.length; i++)
            System.out.println(result);
//This looks better to me.
result = input.split(pattern);
for (int i = 0; i < result.length; i++)
System.out.println(result[i]);