生成6位随机码含字母大小写+数字

/**
 * Created by Administrator on 2016/11/6.
 */
public class test2 {
    public static void main(String[] args)throws IOException{
        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        str+= str.toLowerCase();
        str +="0123456789";
        System.out.println(str);
        char ch = str.charAt(str.length()-1);
        System.out.println(ch);
        StringBuffer sb = new StringBuffer(6);
        for (int i = 0; i <6 ; i++) {
            char ch2 = str.charAt(new Random().nextInt(str.length()));
            sb.append(ch2);
        }
        System.out.println(sb);
    }
}

生成方法很多，也可以用Math来做