Java根据正整数的位数并逆序打印出各位数字

题目：给一个不多于5位的正整数，要求：一、求它是几位数，二、逆序打印出各位数字。

程序设计：

import java.util.scanner;
public class ex24 {
public static void main(string[] args) {
  ex24 tn = new ex24();
  scanner s = new scanner(system.in);
  long a = s.nextlong();
  if(a < 0 || a > 100000) {
  system.out.println("error input, please run this program again");
  system.exit(0);
  }
  if(a >=0 && a <=9) {
  system.out.println( a + "是一位数");
  system.out.println("按逆序输出是" + '\n' + a);
  } else if(a >= 10 && a <= 99) {
  system.out.println(a + "是二位数");
  system.out.println("按逆序输出是" );
  tn.converse(a);
  } else if(a >= 100 && a <= 999) {
  system.out.println(a + "是三位数");
  system.out.println("按逆序输出是" );
  tn.converse(a);
  } else if(a >= 1000 && a <= 9999) {
  system.out.println(a + "是四位数");
  system.out.println("按逆序输出是" );
  tn.converse(a);
  } else if(a >= 10000 && a <= 99999) {
  system.out.println(a + "是五位数");
  system.out.println("按逆序输出是" );
  tn.converse(a);
  }
}
public void converse(long l) {
  string s = long.tostring(l);
  char[] ch = s.tochararray();
  for(int i=ch.length-1; i>=0; i--) {
  system.out.print(ch[i]);
  }
}
}