import java.util.Scanner;

public class TestCharcount1 {
public static void main(String []args) {
int strNum = 0;
int numNum = 0;
int spcNum = 0;

    Scanner scanner = new Scanner(System.in);
    System.out.print("请输入字符串:");
    String str = scanner.nextLine();
    Character[] c = new Character[str.length()];
    
    for(int i = 0; i < str.length(); i++) {
        c[i] = str.charAt(i);
        
        for(char j = '0'; j <= '9'; j++)
            if(c[i] == j)
                numNum++;
                
        for(char j = 'a'; j <= 'z'; j++)
            if(c[i] == j)
                strNum++;
                
        for(char j = 'A'; j <= 'Z'; j++)
            if(c[i] == j)
                strNum++;
                
        if(Character.isWhitespace(c[i]))
            spcNum++;
    }
    
    System.out.println("strNum=" + strNum);
    System.out.println("numNum=" + numNum);
    System.out.println("spcNum =" + spcNum);
}

}
输出:
strNum=21
numNum=2
spcNum=6