Exam 3. Simple Expression

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class _3_SimpleExpression {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scan = new Scanner(System.in);
        String inputLine = scan.nextLine().trim();

        Pattern numberPatt = Pattern.compile("\\d{1,10}([.]*([0-9]{0,9}))*");
        Matcher matcher = numberPatt.matcher(inputLine);
        ArrayList<BigDecimal> numbers = new ArrayList<>();
        String numStr;
        while (matcher.find()) {
            numStr = matcher.group();
            numbers.add(new BigDecimal(numStr));
        }

        Pattern operatorPatt = Pattern.compile("\\+|\\-");
        matcher = operatorPatt.matcher(inputLine);
        ArrayList<String> operators = new ArrayList<>();
        while (matcher.find()) {
            operators.add(matcher.group());
        }

        BigDecimal sumOfNumbers = numbers.get(0);
        for (int i = 1; i < numbers.size(); i++) {
            if (operators.get(i - 1).equals("+")) {
                sumOfNumbers = sumOfNumbers.add(numbers.get(i));
            } else if (operators.get(i - 1).equals("-")) {
                sumOfNumbers = sumOfNumbers.subtract(numbers.get(i));
            } else {
                throw new IllegalArgumentException("Invalid operator: "
                        + operators.get(i - 1));
            }
        }

        System.out.println(sumOfNumbers.toPlainString());
    }
}