方法一
private static int getNumLenght(long num){
        num = num>0?num:-num;       
        return String.valueOf(num).length();

    }

方法二
private static int getNumLenght(long num){
        num = num>0?num:-num;       
        if (num==0) {
            return 1;
        }
        return (int) Math.log10(num)+1;
    }

方法三
private static int getNumLenght(long num){
        if (num==0) {
            return 1;
        }
        int lenght = 0;
        for (long temp = num ; temp != 0; temp/=10){
            lenght++;
        }
        return lenght;
    }

多種方法求java求整數的位數