具体的Stream用法可以参考：List.stream() 各方法应用_Bulldozer Coder的博客-CSDN博客

List<MyBingeWatchBean> checkList = adapter.getCheckList();
String docids = "";
if(checkList!=null&&checkList.size()>0){
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
        docids = checkList.stream().map(it->it.getDoc_id()).collect(Collectors.joining(","));
    }else {
        for (int i = 0; i < checkList.size(); i++) {
            MyBingeWatchBean documentBean = checkList.get(i);
            docids = documentBean.getDoc_id()+","+docids;
        }
    }
    documentViewModel.deleteFollowDecumentary(docids);
}

用流操作的确简介很多