将对象列表中的双列表对象转换为字符串

Question

I am having a list of data objects. Each data object has a resultList of double elements which can also be null.

I want pull out this resultList of the data object and store them seperately in a string list:

List<List<String>> ar_List = new ArrayList<List<String>>();
for (int i = 0; i < dataList.size(); i++) {
    for (int j = 0; j < dataList.get(i).getResultList().size(); j++) {
        ar_List.add(dataList.get(i).getResultList().get(j).toString());
    }
}

However I still get an error at ar_List.add(dataList.get(i).getResultList().get(j).toString());

Any recommendations how to write the List Objects into ar_List ?

I appreciate your answers!

Answer 1

replace

ar_List.add(dataList.get(i).getResultList().get(j).toString());

with

ar_List.get(i).add(dataList.get(i).getResultList().get(j).toString());

Answer 2

Check if the data is null because calling toString() on a null object causes a NPE. And you need to get the List<String> and not List<List<String>>

if(dataList.get(i).getResultList().get(j) != null) {
       ar_List.get(i).add(dataList.get(i).getResultList().get(j).toString());
}

In order to check for null lists either filter the parent list for null objects or change the for condition.

for(in j = 0; j < dataList.get(i).getResultList().size(); dataList.get(i).getResultList().get(j)==null?j+=2:j++)

This jumps over the next row if the next row is null. But the better would be to clean the list.