Jayasagar

Map<String, Map<Thing, Boolean>> consumerWithEachDeviceStatus = consumerList
        .stream()
        .flatMap(consumer -> consumer.getThings()
                .stream()
                .map(thing -> new AbstractMap.SimpleImmutableEntry<>(consumer.getName(), thing))
        )
        .collect(Collectors.groupingBy(entry -> entry.getKey(),
                Collectors.toMap(AbstractMap.SimpleImmutableEntry::getValue, entry -> entry.getValue().isRunning())));

System.out.println(consumerWithEachDeviceStatus);

Jayasagar

boolean bobAllDevicesRunning = consumerList
                .stream()
                .filter(consumer -> "Bob".equals(consumer.getName()))
                .flatMap(consumer -> consumer.getThings().stream())
                .allMatch(Thing::isRunning);
System.out.println(bobAllDevicesRunning);
// Output : true

Jayasagar

boolean isAlDevicesRunnig = consumerList
                .stream()
                .flatMap(consumer -> consumer.getThings().stream())
                // 'allMatch' is a terminal operation
                .allMatch(Thing::isRunning);
System.out.println(isAlDevicesRunnig);
// Output : true

Jayasagar

Map<String, Integer> consumerWithTotalAmount = consumerList
        .stream()
        .flatMap(consumer -> consumer.getThings()
                .stream()
                .map(thing -> new AbstractMap.SimpleImmutableEntry<>(consumer.getName(), thing.getCost()))
        ).collect(Collectors.groupingBy(AbstractMap.SimpleImmutableEntry::getKey,
                Collectors.mapping(entry -> entry.getValue(), Collectors.summingInt(value -> value))));

System.out.println(consumerWithTotalAmount);
// Output: {Bob=680, Satti=360, Sri=320, Malli=180}

Jayasagar

Map<Type, Set<String>> allUsersByDeviceType = consumerList
        .stream()
        .flatMap(consumer -> consumer.getThings()
                .stream()
                .map(thing -> new AbstractMap.SimpleImmutableEntry<>(thing.getType(), consumer.getName()))
        ).collect(Collectors.groupingBy(AbstractMap.SimpleImmutableEntry::getKey,
                Collectors.mapping(entry -> entry.getValue(), Collectors.toSet()))
        );

System.out.println(allUsersByDeviceType);

Jayasagar

// How to loop over nested collections referring to parent elements?
List<Consumer> allConsumersWhoHasHealthDevice = consumerList
        .stream()
        .flatMap(consumer -> consumer.getThings().stream()
                .filter(thing -> thing.isRunning() && Type.HEALTH == thing.getType())
                // This is cool!!!
                .map(thing -> new AbstractMap.SimpleImmutableEntry<>(consumer, thing))
        )
        .map(entry -> entry.getKey())
        .collect(Collectors.toList());

Jayasagar

// How to loop nested collection using lambda streams?
Set<Event> allActiveDeviceOperations = consumerList
        .stream()
        // 'flatMap' intermediate operation, here produces the stream of user Things(Devices)
        .flatMap(consumer -> consumer.getThings().stream())
        .filter(thing -> thing.isRunning())
        .flatMap(thing -> thing.getEvents().stream())
        .collect(Collectors.toSet());
System.out.println(allActiveDeviceOperations);
//Output : [Event(name=motionCaptured), Event(name=switchedOff), Event(name=switchedOn), Event(name=virusFound), Event(name=dryField)]

Jayasagar

consumerList
        .stream()
        // map intermediate operation
        // 'map' is used to transform one element type into other, here we transformed Consumer into String
        .map(Consumer::getName)
        // 'distinct' intermediate operation
        .distinct()
        // 'sorted' intermediate operation
        .sorted()
        // 'reduce' terminal operation

Jayasagar

boolean isAnyConsumerInBerlin = consumerList
                .stream()
                // anyMatch terminal operation
                .anyMatch(consumer -> "Berlin".equals(consumer.getCity()));
System.out.println(String.format("Are there any user based in Berlin: %b", isAnyConsumerInBerlin));
// Output: Are there any user based in Berlin:true

Jayasagar

List<String> uniqueCities = consumerList
                .stream()
                .map(Consumer::getCity)
                .distinct()
                .collect(Collectors.toList());
System.out.println(uniqueCities);
// Output: [Hyd, Berlin]