题解 | #统计字符#

这里主要考察的还是字符串中单个字符怎么判断是数字还是字母：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.nextLine();
        int len = s.length();
        // 定义计数器
        int c_letter = 0;
        int c_black = 0;
        int c_num = 0;
        int c_other = 0;
        // 循环遍历这个字符串
        for(int i = 0; i < len; i++) {
            char c = s.charAt(i);
            if(isLetter(c)) {
                c_letter ++ ;
            } else if(c == ' ') {
                c_black ++ ;
            } else if(isNum(c)) {
                c_num ++;
            } else {
                c_other ++ ;
            }
        }
        System.out.print(c_letter + "\n" + c_black + "\n" + c_num + "\n" + c_other + "\n");
    }

    // 验证字符是否是数字
    public static boolean isNum(char c) {
        return Character.isDigit(c);
    }

    // 验证字符是否是字母
    public static boolean isLetter(char c) {
        boolean c1 = c >= 'A' && c <= 'Z';
        boolean c2 = c >= 'a' && c <= 'z';
        return c1 || c2;
    }
}