I’ve a two POJOs, Sample code below Controller class This returns me a list of the list: but what I want is a single list like How can I do that with Java 8 streams? I’ve tried flatMap also, but that doesn’t go well with the Object datatype of entries. Answer Consider a List<String> as…
Tag: list
How convert JavaRDD to JavaRDD<List>?
I try make it with use this code, but I get WrappedArray How make it correctly? Answer You can use getList method: where lemmas is the name of the column with lemmatized text. If there is only one column (it looks like this is the case) you can skip select. If you know the index of the column you can
trouble initialize List Using Arrays.asList
When I initialize List, I am able to do this: But when I want to simplify it using Arrays.asList: It cannot compile with error: Why it cannot do the type inference right and how to fix this? Answer Remember that … is just syntactic sugar for an array parameter. You can call a method with a variadic para…
How to [flat] merge Merge Multiple Arrays into List in Java
How can I [flat] merge multiple arrays into a single List<String>? For example: Answer Assuming that you wish to add the array of Integers into the same List of Strings:
Declaring initial capaity for a list in java is a bad technique?
I have multiple ArrayLists with the same capacity. I fill these lists by reading a file. I know that one difference between an Array and an ArrayList is that the Array have a fixed capacity while the ArrayList have a variable capacity. You should explicitly specify the array length when you declare it, but th…
How to get Cartesian product from multiple lists?
Say I have several List<T>s, I will put them into another list or other collections, so I don’t know how many list<T> I have until I call List<List<T>>.size() Take below List<Integer> as an example: How can I get the result of list1*list2*list3*…listn as a Cartesian p…
Incompatible types List of List and ArrayList of ArrayList
The below line gives me error : What is the reason? EDIT I understand if I change my second ArrayList to List, it does not give me error. I want to know the reason of error though. Thanks Answer If you had a List<List<Integer>> then you’d be able to add a LinkedList<Integer> to it. But…
Merge lists with stream API
I have the following situation I have to merge all the lists lst from the ListContainer objects from a Map map. Any idea how, using Java 8 stream API? Answer I think flatMap() is what you’re looking for. For example:
How to implement a round-robin circular list and count access requests of an element?
Scenario: For a list that have 3 elements: You can circular access it as many times as you want. And there is an additional counting function records access count of each element. For example, if accessing it 7 times, should return: And have access count of each element as following: Add another additional fu…
Jackson read json in generic List
I’m using Jackson in order to read json messages. One of the values that I’ trying to parse is a List and another value contains the type of the data in the list. This is the structure i ‘ve created in java. Through Class.forName(); I can get the class which represents the data in the list. …