public class STR { private static String Builderrud(int a){ StringBuilder builder= new StringBuilder(); //调用StringBuilder类 for (int j=0;j<a;j++){ builder.append(j); //Builder类的追加功能 } String builder1=String.valueOf(builder); System.out.printf(builder1); //调试打印 return builder1; }; public static void main(String[] args) { //主函数调用 Builderrud(40); //40位随机数,要包含字母的话可修改追加 } }