Java Stream why does reduce requires two parameters of the functional Interface?

In other words, why does reduce require BinaryOperator, or BiFunction interface? Why doesn’t it use UnaryOperator, or Function interface instead? What is the point of having two parameters as the …

parallel() not work with the 3-arg iterate()

Here is my code: int count=20; Stream.iterate(4,i->ii+1).parallel().forEach(i -> { try { Thread.sleep(new Random().nextInt(2000)); } catch (InterruptedException …

Map List to Map with additional transformation

I need to convert a list of objects to a map of sets of one of the objects’ property and I’d like to use Java streams for that. For example there is a List and I’d like to convert it to a …

Are stream elements sorted? [closed]

Is there a way to find if the elements taken from a Stream in encounter order, are all sorted in ascending order? (The stream source could be absolutely anything, from Arrays.stream() to Files.lines(),…

How to Iterate list of list of Java Objects using Java 8

How to iterate and get through list of list of objects using Java 8 Also need to get the count of distinct customerIds final List issues = customerIssues.collectList().block(); …

‘OptionalDouble.getAsDouble()’ without ‘isPresent()’ check

I’ve seen a bunch of solutions for this question but no matter what I try, IDEA still reports an error. Consider the following block: double testDouble= customClass.stream() .mapToDouble(…

Combine similar elements in a Java Stream

How to combine consecutive similar objects that are in a Java Stream? Till now I could not find a good solution, so I hope you can help. Suppose we have a class like the following: class Someclass { …

How to map a stream of class objects into a stream of properties of said class?

I have a class that has 3 properties, all with the same data type, let’s say: Class Test { int i; int j; int k; } Then, I have a stream containing test classes (assume all the properties …

How to compare two maps with different values using the Stream API? [closed]

There are two maps and a method that accepts them and returns a new map. Maps contain the same number of the same keys, but their values ​​are different. Map a = new HashMap&…

Report on a multimap by producing a new map of each key mapped to the count of elements in its collection value

Imagine a multimap tracking persons, each of whom has a list of assigned tasks. Map< Person , List > personToTasks = Map.of( new Person( “Alice” ) , List.of(…