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Tag: collections

Java Stream Collect() classifier can’t detect type

I have the following code reading lines from a text file: The text file has data like And I’m trying to group by String1 and String2 and get their counts. Then end result should be a Map<String, Map<String, Long>>. However, with the code above, the compiler is saying that the collect() returns a ConcurrentMap <Object, ConcurrentMap<Object, Long>>. Why are the

Java List Stream

I am attempting to simplify my code but list stream is not working. I am creating an instance of a class (that contains an inner class) in a static method and trying to take items from the first list and instantiate them in the inner class and add them to a new list. My code works with fruit loops if

How to write a method that takes in a List of Integer, Float, Double and calculate the average?

I am trying to write a method that takes in a list of numeric values – eg List<Integer>, List<Float>, List<Double> etc – and give me the average. These are the errors I get: Operator ‘+’ cannot be applied to ‘capture<? extends java.lang.Number>’, ‘capture<? extends java.lang.Number>’ Answer OptionalDouble average() Where, OptionalDouble is a container object which may or may not contain

Mapping pair of elements into one with Stream IPA

So I’m wondering what is the best solution to the following problem: I have a list of items (a custom class) in a java collection ex Each item in the collection however has a corresponding logical pair also in the collection (so the pair’s are not necessarily following each other by index in the collection) I have a helper method

Why list.contains(null) throwing null pointer exception?

I have List<Long> countriesList which contains Long values which are country ids. Now I am iterating over some List<UserRequests> list by using streams. I tried to debug by evaluating individual statements. I have made sure countriesList have some data First part CollectionUtils.isNotEmpty(countriesList) is returning true. userRequest is also not null but userRequest.getCountryId() is null. And when I evaluated countriesList.contains(userRequest.getCountryId()), I

remove (and count) duplicates from a list

Is it possible to iterate between two iterators of a same list and remove an item within the nested iterator? Version 1 (does not work): } I get a java.util.ConcurrentModificationException, because I modify an element within the same iterator.. I can solve this issue by using another list removableItems and put those items in it: Version 2 (works): Is there

Map a List to DTO inside map – java

I have such collection: Map<Integer, List<MyObject>> collection I would like to map the whole list of MyObject to MyObjectDTO and return the whole map with the mapped list. So return will be: Map<Integer, List<MyObjectDto>> collectionWithDtos What is the easiest and quickest way? I’ve checked a couple of ways with streams but none of that produced results as I expected. Thanks

Create and find highest value in subarraylist

I have an Arraylist of the Cells from an Excel sheet. I want to create subarraylists of size 50 from the Arraylist of Cells I actually have, beginning from the index of 1590 and ending with size()-700. I want to get the highest number from every subarraylist and put it in the new Arraylist. in the new Arraylist there should