要是在toString（）中使用循环，建议用下面的方法

    1. public class UsingStringBuilder {
    2.     public static Random rand = new Random(47);
    3.     public String toString(){
    4.         StringBuilder result = new StringBuilder("[");
    5.         for (int i = 0; i <10 ; i++) {
    6.             result.append(rand.nextInt(100));
    7.             result.append(",");
    8.         }
    9.         result.append("]");
    10.         return result.toString();
    11.     }
    13.     public static void main(String[] args) {
    14.         UsingStringBuilder usb = new UsingStringBuilder();
    15.         System.out.println(usb);
    16.     }
    17. }
    18. 输出：
    19. [58,55,93,61,61,29,68,0,22,7,]