a simple string calculator in java

StringCalculator.java

import java.util.ArrayList;
import java.util.Scanner;

public class StringCalculator {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		ArrayList<Double> numbers = new ArrayList<>();
		ArrayList<Character> operators = new ArrayList<>();
		String number = "";

		// getting the user expression.
		String expression = scanner.nextLine();
		scanner.close();

		for (int i = 0; i < expression.length(); i++) {
			switch (expression.charAt(i)) {
			case '+': {
				operators.add('+');
				numbers.add(Double.parseDouble(number));
				number = "";
				break;
			}
			case '-': {
				operators.add('-');
				numbers.add(Double.parseDouble(number));
				number = "";
				break;
			}
			case '*': {
				operators.add('*');
				numbers.add(Double.parseDouble(number));
				number = "";
				break;
			}
			case '/': {
				operators.add('/');
				numbers.add(Double.parseDouble(number));
				number = "";
				break;
			}
			case '^': {
				operators.add('^');
				numbers.add(Double.parseDouble(number));
				number = "";
				break;
			}
			case ' ': {
				break;
			}
			default: {
				number += expression.charAt(i);
			}
			}
		}

		// adding the last number
		numbers.add(Double.parseDouble(number));

		// calculate ^
		for (int i = 0; i < operators.size(); i++) {
			if (operators.get(i) == '^') {
				numbers.set(i, Math.pow(numbers.get(i), numbers.get(i + 1)));
				numbers.remove(i + 1);
				operators.remove(i);
				i--;
			}
		}

		// calculate * and /
		for (int i = 0; i < operators.size(); i++) {
			if (operators.get(i) == '*') {
				numbers.set(i, (numbers.get(i) * numbers.get(i + 1)));
				numbers.remove(i + 1);
				operators.remove(i);
				i--;
			} else if (operators.get(i) == '/') {
				numbers.set(i, (numbers.get(i) / numbers.get(i + 1)));
				numbers.remove(i + 1);
				operators.remove(i);
				i--;
			}
		}

		// calculate + and -
		for (int i = 0; i < operators.size(); i++) {
			if (operators.get(i) == '+') {
				numbers.set(i, (numbers.get(i) + numbers.get(i + 1)));
				numbers.remove(i + 1);
				operators.remove(i);
				i--;
			} else if (operators.get(i) == '-') {
				numbers.set(i, (numbers.get(i) - numbers.get(i + 1)));
				numbers.remove(i + 1);
				operators.remove(i);
				i--;
			}
		}

		System.out.println(expression + " = " + numbers.get(0));
	}
}