随机产生一个数字Java

public CustLib getRandomCustLib(User user, Customer customer){
    GetCustLibImpl getCustLibImpl=new GetCustLibImpl();
    List<CustLib> custLibs=getCustLibImpl.getCustLibs(user);
    if(custLibs.size()<2){
        Log.error("当前客户库数量为0或1，没有办法转移客户库");
       return null;
    }else {
        CustLib custLibNow=new CustLib();
        custLibNow.setId(customer.getLibId());
        custLibNow.setTitle(customer.getLibName());
        custLibs.remove(custLibNow);
　　　　　int num=(int)(Math.random()*(custLibs.size()));
        CustLib custLibNext=new CustLib();
        custLibNext.setId(custLibs.get(num).getId());
        custLibNext.setTitle(custLibs.get(num).getTitle());
        Log.info("随机获取的libId："+custLibNext.getId());
        Log.info("随机获取的libName："+custLibNext.getTitle());
        return custLibNext;
    }
}