1 Scanner sc=new Scanner(System.in); 2 String a="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; 3 4 for(int i=0;i<4;i++) 5 { 6 Random r=new Random(); 7 int s=r.nextInt(62); 8 System.out.println("随机生成的4位字母和数字为:"+a.substring(s,s+1)); 9 10 }