Java-Array List实现随机数生成，乱序不重复

public class Test903 {
    public static void main(String[] args) {
        ArrayList arrayList=new ArrayList();
        Scanner scanner=new Scanner(System.in);
        int f=scanner.nextInt();
        while(arrayList.size()<74){
            if (arrayList.size()<1){
                arrayList.add(num(f));
            }
           int  j= num(f);
            //判断是否已经存在，不重复的关键
            boolean b=arrayList.contains(j);
            if(b==false){
                arrayList.add(j);
                //System.out.println(arrayList);
            }
        }
        //循环输出，可以自定义
        for (int i = 0; i <arrayList.size() ; i++) {
            System.out.println(arrayList.get(i));
        }
    }
    //生成一个随机数
    public static int num(int f) {
        Random random=new Random();
        //+1是为了过滤0，并包含f
        return random.nextInt(f)+1;
    }
}