java输出一个字符串里面的空格，字母和数字的个数

9.3 输出一个字符串里面的空格，字母还有数字的数目。    

public class Test {
    public static void main(String[] args) throws IndexOutOfBoundsException {
        String a = "I am a student whose age is 20";
        shumu(a); //输出字符串空格和字母还有数字的数目。
    }

    static void shumu(String a) {
        int shuzi = 0, zimu = 0, kongge = 0;
        char[] c = new char[a.length()];
        for (int i = 0; i < a.length(); i++) {
/*下面这句话是java自带的函数，意思是对于某一个字符串,取出某个位置的字符。@马克-to-win*/
            c[i] = (char) a.codePointAt(i);
            if (c[i] >= '0' && c[i] <= '9') {
                shuzi++;
            }
            if ((c[i] >= 'A' && c[i] <= 'Z') || (c[i] >= 'a' && c[i] <= 'z')) {
                zimu++;
            }
            if (c[i] == ' ') {
                kongge++;
            }
        }