Java中十六进制字符串转为原字符串(26英文字母)

public static String fromHexStringToString(String str){
char[] c = str.toCharArray();
StringBuilder builder = new StringBuilder();
for (int i = 0; i < c.length-1; i+=2) {
int num = (c[i]-'0')*16+(c[i+1]-'0')*1;
builder.append((char) num);
}
return builder.toString();
}