java计算a+aa+aaa+aaaa的和

 1 public class Test {
 2     public static void main(String[] args) {
 3         /*
 4          * 求a+aa+aaa+aaaa的和
 5          */
 6         int a = 1;
 7         int n = 3;
 8         int num = 0;
 9         int sum = 0;
10         // 循环是输出 a aa aaa  
11         //所以还要用sum相加
12         for (int j = 0; j < n; j++) {
13             num = num * 10 + a; // 1 11
14             System.out.print(num + "\t");
15             sum += num;
16         }
17         System.out.println();
18         System.out.println(sum);
19     }
20 
21 }
22 //执行结果：
23 1    11    111    
24 123