How to assign incremental values to lists in Java 8

Suppose you have a list of objects The list is sorted by one or more fields of the object So according to the sort list, I want to set the field of the object with incremental value

public class ObjectTest {
   int id;
   int userId;
   int code;
}

As mentioned above, objecttest, any user has its own code There is an objecttest list

List<ObjectTest> objTests;

It sort:

objTests.sort(Comparator.comparing(DataSet::getUserId).thenComparing(DataSet::getCode));

Therefore, after sorting by userid and code, I want to set the value from 1 to any user has its own code When the userid changes, the increment value is reset to 1 again

If you have the following objecttest set

id     userId    code
--------------------------------
             100     5
             200     6
             100     7
             200     9
             200     10
             100     2

After explaining the above scenario, the following sets will be:

id      userId     code
1        100        2
2        100        5
3        100        7
1        200        6
2        200        9
3        200        10

Can I use lambda expressions in Java

Solution

Some things should work:

List<ObjectTest> resultSet = 
objTests.stream()
        .sorted(Comparator.comparing(ObjectTest::getUserId).thenComparing(ObjectTest::getCode))
        .collect(Collectors.groupingBy(ObjectTest::getUserId,LinkedHashMap::new,Collectors.toList()))
        .values()
        .stream()
        .map(e -> {
            IntStream.range(0,e.size())
                    .forEach(i -> e.get(i).setId(i + 1));
            return e;
        })
        .flatMap(Collection::stream)
        .collect(Collectors.toList());

Note that I haven't compiled this code yet