JAVA生成8位随机字符串，数字+英文字母

public String genRandomNum(){
	  int  maxNum = 36;
	  int i;
	  int count = 0;
	  char[] str = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K',
	    'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
	    'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };	  
	  StringBuffer pwd = new StringBuffer("");
	  Random r = new Random();
	  while(count < 8){
	   i = Math.abs(r.nextInt(maxNum));   
	   if (i >= 0 && i < str.length) {
	    pwd.append(str[i]);
	    count ++;
	   }
	  }
	  return pwd.toString();
	}

该方法加形参，可以改造为生成任意位数的随机字符串