统计字符次数

键盘录入一个字符串，统计该字符串中大写字母字符，小写字母字符，数字字符出现的次数 (不考虑其他字符)

import java.util.Scanner;

public class StringDemo {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("输入一个字符串");
    String str = sc.nextLine();
    int bigCount = 0;
    int smallCount = 0;
    int numberCount = 0;
    for (int i = 0; i < str.length(); i++) {
      char c = str.charAt(i);
      if (c >= 'a' && c <= 'z') {
        smallCount++;
      } else if (c >= 'A' && c <= 'Z') {
        bigCount++;
      } else if (c >= '0' && c <= '9') {
        numberCount++;
      }
    }
    System.out.println("大写字母有" + bigCount + "个");
    System.out.println("小写字母有" + smallCount + "个");
    System.out.println("数字有" + numberCount + "个");
  }
}