java-stream

Im new to Java 8 Streams and would like to convert following code-block to Java 8's Stream way of doing the same thing. Edit : Updates the class-names to be less confusing. (Removed Foo, Bar, Baz...) ArrayList<PriceList> priceLists = new ArrayList<PriceList>(); // I'm casting to a type-safe List from getObjects() // -which is a function I dont have access to. Is there a nice // solution to embed this in the stream-syntax? List<PriceListGroup> distObjects = (List<PriceListGroup>) objects.get(1).getObjects(); for(PriceListGroup group : distObjects) { Set<Affiliate> affiliates = group

Im trying to use Java 8 streams to combine lists. How can I get a "symmetric difference list" (all object that only exist in one list) from two existing lists. I know how to get an intersect list and also how to get a union list. In the code below I want the disjoint Cars from the two lists of cars (bigCarList,smallCarList). I expect the result to be a list with the 2 cars ("Toyota Corolla" and "Ford Focus") Example code: public void testDisjointLists() { List<Car> bigCarList = get5DefaultCars(); List<Car> smallCarList = get3DefaultCars(); //Get cars that exists in both lists List<Car>

I'm creating a very simple form validation utility for a sign up screen, and I'm running into some unexpected behavior concerning LinkedHashMap and a stream created from its entrySet . I'm storing validation results in a LinkedHashMap , with the following ordering of statements: Map<ValidationResult.SignUpField, Boolean> fieldStatuses = new LinkedHashMap<>(); fieldStatuses.put(EMAIL, isValidEmail(emailAddress)); fieldStatuses.put(USERNAME, isValidUsername(username)); fieldStatuses.put(BIRTHDAY, isValidBirthday(birthday)); fieldStatuses.put(PASSWORD, isValidPassword(password)); fieldStatuses

This question already has answers here : :: (double colon) operator in Java 8 (17 answers) Closed 3 years ago . Edit: My question here was answered. To summarize, I was confused about the usage of non-static method references. There the functional interface and referenced method have a different number of parameters. What answered my question is the comment and the accepted answer. I am currently reading the Java Tutorial about Stream reduction methods ( https://docs.oracle.com/javase/tutorial/collections/streams/reduction.html ). There I found a piece of code that I thought was wrong, so I

If I have a collection: List<Long> numbers = asList(2, 2, 4, 5); How can I map/process these to build up a running total. To produce something like: List<Long> runningTotals = asList(2, 4, 8, 13); Even better, how can I build a list of something (like a tuple) so I can preserve the orignals: ((2 -> 2), (2 -> 4), (4 -> 8), (5 -> 13)); Update : As Holger pointed out in the comments using Stream.reduce() for this purpose is not correct. See Reduction and Mutable Reduction or Java 8 Streams - collect vs reduce for more information. You can use Java Stream.collect() instead to generate your list

Is there naming convention for methods that return Stream? The only mention I found is this answer on S.O (last paragraph), but I don't see what is it based on. Since I wrote that paragraph I feel compelled to answer. :-) Suppose you have a class that represents an aggregation of things of a single type, and you want to return a Stream of them to the caller. If it's totally unambiguous as to what you're returning, you might just as well call the method stream() . There are a lot of methods in the JDK named stream() that return a stream of the obvious type. Sometimes what you're returning is

I have an enum with another enum as a parameter public enum MyEntity{ Entity1(EntityType.type1, .... MyEntity(EntityType type){ this.entityType = entityType; } } I want to create a method that return the enum by type public MyEntity getEntityTypeInfo(EntityType entityType) { return lookup.get(entityType); } usually I would have written private static final Map<EntityType, EntityTypeInfo> lookup = new HashMap<>(); static { for (MyEntity d : MyEntity.values()){ lookup.put(d.getEntityType(), d); } } What is the best practice to write it with java stream? Alexis C. I guess there are some typos in

I have the following lambda expression and if works fine when bonusScheduleDurationContainers is not empty. If it is empty, I get a NoSuchElementException . How do I check this in the lambda expression? final List<ScheduleDurationContainer> bonusScheduleDurationContainers = scheduleDurationContainersOfWeek.stream() .filter(s -> s.getContainerType() == ScheduleIntervalContainerTypeEnum.BONUS) .collect(Collectors.toList()); final ScheduleDurationContainer bonusScheduleDurationContainer = bonusScheduleDurationContainers.stream() .filter(s -> s.getDayOfWeekStartingWithZero() == dayOfWeekTmp)

So, finally making a relatively large jump from Java 6 to Java 8, I've read up a fair amount of Java 8 Streams API. Unfortunately, almost all the examples that have been asked are almost close to what I'm trying to figure out how to do, but not close enough. What I have is final List<Function<? super Double, Double>> myList = generateList(); final double myVal = calculate(10); private double calculate(double val) { for (Function<? super Double, Double> function : this.myList) { val += function.apply(val); } return val; } Now, I've come to understand I could do something similar with .stream()