parseComplex

public static ComplexNumber parse(String s) throws NumberFormatException {
    boolean[] signs = { true, true };
    String[] numbers = { "", "" };
    double re = 0.0;
    double im = 0.0;

    if (s.startsWith("-")) {
        signs[0] = false;
        s = s.substring(1);
    } else if (s.startsWith("+")) {
        s = s.substring(1);
    }

    if (s.contains("-")) {
        signs[1] = false;
        numbers = s.split("-");
    } else if (s.contains("+")) {
        numbers = s.split("\\+");
    } else {
        numbers[0] = s;
    }

    for (int i = 0; i < 2; i++) {
        if (numbers[i].contains("i")) {
            if (numbers[i].equals("i")) {
                im = 1;
            } else {
                im = Double.parseDouble(numbers[i].replace("i", ""));
            }
            if (!signs[i]) {
                im = -im;
            }
        } else if(!numbers[i].equals("")){
            re = Double.parseDouble(numbers[i]);
            if (!signs[i]) {
                re = -re;
            }
        }
    }

    return new ComplexNumber(re, im);
}