如何用java语言编写“求一个字符串中的的字母，数字，空格的数目。”

public class StringNumber {
private String str=" ";
private int z=0;
private int k=0;
private int g=0;
public StringNumber(String str){
this.str=str;
}
public void strNumber(){
byte buf[]=str.getBytes();

for(int i=0;i<str.length();i++){
if(buf[i]==' '){
z++;
}
if((buf[i]>='0')&&(buf[i]<='9')){
k++;
}
if(((buf[i]>='a')&&(buf[i]<='z'))||((buf[i]>='A')&&(buf[i]<='Z'))){
g++;
}
}

System.out.println("空格数是"+z);
System.out.println("数字个数"+k);
System.out.println("字母个数"+g);

}

public static void main(String[] args) {
// TODO: 在这添加你的代码

StringNumber strnumber = new StringNumber("aaasdfdsfdsf  fdAADD3432 erew34");

strnumber.strNumber();

}
}

方法二：
public class Test
{
public static void main(String[] args)
{
int space = 0, number = 0, character = 0;
String str = "23 ffa 4fasd";
for (int i = 0; i < str.length(); i++)
{
char ch = str.charAt(i);
if (ch == ' ')
{
space++;
}
if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))
{
character++;
}
if (ch >= '0' && ch <= '9')
{
number++;
}
}
System.out.println("number: " + number);
System.out.println("character: " + character);
System.out.println("space: " + space);
}
}