Compare two Lists and get the difference [duplicate]

Question

I have two Lists which I get - one from xlsx file, the second one - by select from database

@Component
public class ReadExcelDemo implements CommandLineRunner {

    @Autowired
    private TakeDataService dataService;

    private List<Integer> list;
    private List<TakeData> dates;



    @Override
    public void run(String... args) {
        try
        {
            FileInputStream file = new FileInputStream("Report.xlsx");

            XSSFWorkbook workbook = new XSSFWorkbook(file);

            XSSFSheet sheet = workbook.getSheetAt(0);

            for (Row row : sheet) {
                Iterator<Cell> cellIterator = row.cellIterator();

                while (cellIterator.hasNext()) {
                    Cell cell = cellIterator.next();
                    if (cell.getCellType() == Cell.CELL_TYPE_NUMERIC) {
                        if (cell.getColumnIndex() == 0) {
                            list = new ArrayList<>();
                            list.add((int) cell.getNumericCellValue());
                            //System.out.println(list);
                        }
                    }
                }
            }
            file.close();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        takeData();
        printDifference();
    }

    public void takeData() {
        dates = new ArrayList<>(dataService.takeData());
       // System.out.println(dates);
    }

    public void printDifference() {

        List<Integer> id = dates.stream().map(TakeData::getId).collect(Collectors.toList());

//        for (Integer a : list) {
//            id.remove(a);
//        }
        
//List<Integer> difference = new ArrayList<>(CollectionUtils.disjunction(list, id));
        
        Set<Integer> diff = new HashSet<>(id);
        System.out.println(list.stream().filter(((Predicate<? super Integer>) diff :: contains).negate()).collect(Collectors.toList()));

    }
}

I need to find the difference between these Lists and just print the result of this difference to the console. I have already tried many routers, but most likely it's not the implementation, but something else.

Answer 1

If you're using apache common-collections, try using the below, otherwise there's plenty other options shared in Joe's link

List<Integer> list1 = Arrays.asList(1, 2, 3);
List<Integer> list2 = Arrays.asList(1, 4, 5);

Collection<Integer> list1WithoutList2 = CollectionUtils.removeAll(list1, list2);
System.out.println(list1WithoutList2); //Prints 2,3

Collection<Integer> list2WithoutList1 = CollectionUtils.removeAll(list2, list1);
System.out.println(list2WithoutList1); //Prints 4,5


System.out.println(Stream.concat(list1WithoutList2, list2WithoutList1).toSet()); //Prints 2,3,4,5

Answer 2

Plain Java implementation:

public static void main(String[] args) {
    List<Integer> list = List.of(1,2,3,4,5);
    List<Integer> target = List.of(1,2,3,40,50);
    List<Integer> result = list.stream().filter(v -> !target.contains(v)).collect(Collectors.toList());

    // Prints [4, 5] - items in the list not found in the target
    System.out.println(result);
}