public class Main {
public static void main(String[] args){
//例如100转为7进制数
System.out.println(Integer.valueOf(convertToBase7(100)));
}
public static String convertToBase7(int num) {
StringBuilder sb = new StringBuilder();
if (num == 0) return "0";
boolean flag = num < 0;
num = Math.abs(num);
while (num != 0) {
sb.append(num % 7);
num /= 7;
}
if (flag)
sb.append("-");
return sb.reverse().toString();
}
}