java生成不重复的随机数

public class Demo {
    public static void main(String[] args) {
        int[] a = new int[]{-1,-1,-1,-1};//初始化数组
        Random random = new Random();
        int count = 0;//记录有效的随机数个数
        while(count < a.length){
            boolean flag = true;//用来标志的变量
            int r = random.nextInt(10);
            for(int i=0;i<a.length;i++){
                if(r == a[i]){
                    flag = false;
                    break;
                }
            }
            if(flag){
                a[count] = r;
                System.out.println(r);
                count++;
            }
        }
    }
}