输入一串字符，判断大小写字母和数字各几个

package October;

import java.util.Scanner;

public class Common {
    public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
         //因为scanner.next的默认机制是遇到空格和换行符就会停下
        // 加上这行代码改变它的匹配方式，使得它可以接收空格
      sc.useDelimiter("n");
      String ch = sc.next();
      System.out.println(ch);
      judge(ch);
    }
    public static void judge(String ch) {
        if (ch == null){
            throw new RuntimeException("不能为空");
        }
        int num=0,letter1=0,letter2=0,other=0;
        for(int i = 0; i = '0'&&ch.charAt(i) <= '9'){
                num++;
            }else if(ch.charAt(i) >= 'a'&&ch.charAt(i) <= 'z'){
                letter1++;
            }else if(ch.charAt(i) >= 'A'&&ch.charAt(i)<='Z'){
                letter2++;
            }else {
                other++;
            }
        }
        System.out.println("大写字母有"+letter1+"个"+"n"+"小写字母有"+letter2+"个"+"n"+"数字有"+num+"个"+"n"+"其他字符有"+other+"个");
    }
}