在不使用任何内置函数的情况下，在java脚本中将字符串转换为整数

public class StringToInt {
    public static int convert(String str) {
        if (str == null || str.length() == 0) {
            throw new IllegalArgumentException("Invalid input");
        }

        int result = 0;
        boolean isNegative = false;
        int startIndex = 0;

        if (str.charAt(0) == '-') {
            isNegative = true;
            startIndex = 1;
        }

        for (int i = startIndex; i < str.length(); i++) {
            char c = str.charAt(i);
            if (c < '0' || c > '9') {
                throw new IllegalArgumentException("Invalid character in string");
            }
            int digit = c - '0';
            result = result * 10 + digit;
        }

        return isNegative ? -result : result;
    }

    public static void main(String[] args) {
        String str = "-123";
        int num = convert(str);
        System.out.println("Converted integer: " + num);
    }
}