UseDelimiter("//D")

Question

I got this line "(123     +(45 -3))*4000/-2" read in by a scanner
Scanner scan1= new Scanner(line); //scan by tokens
Scanner scan2 = new Scanner(line).useDelimiter("\\D"); //scan by numbers
The problem is that scan2 takes in the numbers and also white spaces if there are 2 or more arithmetic operators +,-,/,*, or parenthesis ( and )
How do i get rid of the white spaces being read in??

Answer 1

You can split up the regex for more clarity and even expand it with the introduction of decimal numbers like this:import java.util.*;
import java.util.regex.*;
public class Main {
    public static void main(String[] args) { 
        String expression = "(123.3 +(45 -3))*4000/-2";
        String integer = "[0-9]+";
        String decimal = integer+"\\."+integer; // '.' is also a special regex-character!
        String operator = "\\*|\\+|-|/";
        String parenthesis = "\\(|\\)";
        // 'decimal' needs to come before 'integer'
        String regex = decimal+"|"+integer+"|"+operator+"|"+parenthesis;
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(expression);  
        List<String> tokens = new ArrayList<String>(); 
        while(matcher.find()) {
            tokens.add(matcher.group());     
        System.out.println(tokens);
}Checkout this link:
http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html