Java 8 - how to work with lambda with groupingBy and summingInt and use Bitwise operator

Question

I have my own class called CheckIn with attributes day as String , workingHours as int and inProgress as boolean :

public class CheckIn {
    public int id;
    public String day;
    public int workingHours;
    public boolean inProgress;

    public CheckIn(String day, in hours, boolean inProgress) {
        this.day = day;
        this.workingHours = hours;
        this.inProgress = inProgress;
    }
}

And I have list of entries in my system, and I need summary of those entries and group them with days and sum the workingHours. It's Ok here and I'm able to it with lambda, but what if then I want to set is progress to true if there is any in entries is true?

// Suppose this is the inputs 
List<CheckIn> checkinsList = new ArrayList<>();
checkinsList.add(new CheckIn("26-11-2015",6,true));
checkinsList.add(new CheckIn("27-11-2015",6,false));
checkinsList.add(new CheckIn("26-11-2015",6,false));
checkinsList.add(new CheckIn("27-11-2015",4,false));
checkinsList.add(new CheckIn("26-11-2015",1,false));
checkinsList.add(new CheckIn("28-11-2015",6,false));
checkinsList.add(new CheckIn("28-11-2015",6,false));
checkinsList.add(new CheckIn("28-11-2015",6,true));


List<CheckIn> summary = new ArrayList<>();

checkinsList.stream().collect(Collectors.groupingBy(Function.identity(),
    () -> new TreeMap<>(
        Comparator.<CheckIn, String>comparing(entry -> entry.day)),
        Collectors.summingInt(entry -> entry.duration))).forEach((e, sumTargetDuration) -> {
        CheckIn entry = new CheckIn();
        entry.day = e.day;
        entry.duration = sumTargetDuration;
        // Here my something like what I need?
        entry.inProgress = e.inProgress;
        summary.add(entry);
});

I need the summary List contains (in this case for input) have 3 items for those 3 days with :

Result that I want like this :

• First item "26-11-2015" , 13 , true <-- true because there is 1 item for day "26-11-2015" have true.
• Second item "27-11-2015" , 10 , false
• Third item "28-11-2015" , 18 , true

I want the summary come with inProgress true if there is any of entries in that day have inProgress == true is it applicable with lambda?

Answer 1

You need to build a custom Collector for this task. The problem is that there is no built-in collector that will combine multiple collectors together and apply a finishing operation. In this case, we would need to combine 3 collectors: summingInt , reducing , which would or s each inProgress , and mapping , which would map to the day.

The following class will hold the summary during the collection process and calculates the result accordingly. We could add extra-checks regarding the day because it should be the same during the whole process, but I left those out for simplicity.

public class CheckInSummary {

    private int workingHours;
    private boolean inProgress;
    private String day;

    public void accept(CheckIn checkIn) {
        workingHours += checkIn.workingHours;
        inProgress = inProgress || checkIn.inProgress;
        day = checkIn.day;
    }

    public CheckInSummary combine(CheckInSummary summary) {
        workingHours += summary.workingHours;
        inProgress = inProgress || summary.inProgress;
        return this;
    }

    public CheckIn finish() {
        return new CheckIn(day, workingHours, inProgress);
    }

}

Then, you can create a Collector from this class using:

private static Collector<CheckIn, ?, CheckIn> summary() {
    return Collector.of(
                CheckInSummary::new,
                CheckInSummary::accept,
                CheckInSummary::combine,
                CheckInSummary::finish
           );
}

and you can finally use it like this:

List<CheckIn> result = 
      new ArrayList<>(checkinsList.stream()
                                  .collect(groupingBy(c -> c.day, summary()))
                                  .values());

Output from your test case:

[[27-11-2015, 10, false], [26-11-2015, 13, true], [28-11-2015, 18, true]]

This list is not sorted but if you want to sort it, you just need an additional call to sort() comparing the day.