题解 | #统计字符#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextLine()) { // 注意 while 处理多个 case
            String a = in.nextLine();
            System.out.println(a.length()-a.replaceAll("[a-zA-Z]", "").length());
            System.out.println(a.length()-a.replaceAll(" ", "").length());
            System.out.println(a.length()-a.replaceAll("\\d+", "").length());
            System.out.println(a.length()-a.replaceAll("[^a-zA-Z\\d ]", "").length());
        }
    }
}