Java自定义实现String类型转换为int

public class StringToInt {
    
    public static int stringToInt (String str){
        char[] num = str.toCharArray();//得到各个字符的char
        int result = 0;
        for(int i = 0; i < num.length; i++){
            if(num[i]>57||num[i]<48){//0~9对应的Ascall码
                System.out.println("数据格式错误，转换失败！！！");
                throw new NumberFormatException();
            }else{
                result+=(num[i]-48)*(Math.pow(10, num.length-i-1));
            }
        }
        return result;
    }
    
    public static void main(String[] args) {
        String str = "612345";
        //String str="612346a";//错误格式测试
        int sum=stringToInt(str);
        System.out.println(sum);
    }
    
}