Random random = new Random();
static Map tmp = new HashMap();
public static int generate() {
  int i = random.nextInt(100000);
  try {
    return tmp.get(i) == null ? generate() : i;
  } finally {
    tmp.put(i, "");
  }
}

------解决方案--------------------
Random rand= new Random();
Set<Integer> set= new HashSet<Integer>();
while (set.size() < 3)
  set.add(rand.nextInt(30));


------解决方案--------------------
Java code
        int[] array = {0,1,2,3,4,5,6,7,8,9};
        Random rand = new Random();
        for (int i = 10; i > 1; i--) {
            int index = rand.nextInt(i);
            int tmp = array[index];
            array[index] = array[i - 1];
            array[i - 1] = tmp;
        }
        int result = 0;
        for(int i = 0; i < 6; i++)
            result = result * 10 + array[i];
        System.out.println(result);

------解决方案--------------------
public class RandomUtils
{
	private static String[] randomValues = new String[]{"0","1","2","3","4","5","6","7","8","9",
			"a","b","c","d","e","f","g","h","i","j","k","l","m","n","u",
			"t","s","o","x","v","p","q","r","w","y","z"};
	public static String getUsername(int lenght)
	{
		StringBuffer str = new StringBuffer();
		for(int i = 0;i < lenght; i++)
		{
			Double number=Math.random()*(randomValues.length-1);
			str.append(randomValues[number.intValue()]);
		}
		
		return str.toString();
	}

	public static void main(String[] args)
	{
		System.out.println(RandomUtils.getUsername(6));
	}
}
这样就能随机生成六个不同的数了

------解决方案--------------------
不是都说了将曾经生成过的6位数放入HashSet中，随机生成一个数时先判断这个Set中是否存在，如果存在重新再生成一个新的随机数
Java code
Set<Integer> set = new HashSet<Integer>();
Random rand = new Random();
for(int i = 0; i < 10000; i++)
    while(!set.add(rand.nextInt(900000) + 100000));

------解决方案--------------------
	public void general2(){
		List<Integer> list = new ArrayList<Integer>();
		Random random = new Random();
		while (true) {
			 int randomNum = random.nextInt(10);
			 boolean flag = false;
			 for(Integer in : list){
				 if(in == randomNum){
					 flag = true;
					 break;
				 }
			 }
			 if(!flag){
				 list.add(randomNum);
			 }
			 if(list.size()>=6){
				 break;
			 }
		}
		String randomStr = "";
		for (Integer in : list) {
			randomStr += in.toString();
		}
		System.out.println(randomStr);
	}

6位不同的随机数