I have a CSV file which has a header in the first line. I want to convert it to List<Map<String, String>>, where each Map<String, String> in the list represents a record in the file. The key of the map is the header and the value is the actual value of the field. What I have so far: What fur…
Tag: java-stream
Java 8 stream short-circuit
Reading up a bit on Java 8, I got to this blog post explaining a bit about streams and reduction of them, and when it would be possible to short-circuit the reduction. At the bottom it states: Note in the case of findFirst or findAny we only need the first value which matches the predicate (although findAny i…
Convert a for loop to concat String into a lambda expression
I have the following for loop which iterates through a list of strings and stores the first character of each word in a StringBuilder. I would like to know how can I transform this to a lambda expression Answer Assuming you call toString() on the StringBuilder afterwards, I think you’re just looking for…
Implement Cartesian product of several collections by Java Stream
Right now I can only implement the Cartesian product of two collections, here is the code: This code works fine in IntelliJ, but not in Eclipse. Both with compiler compliance level of 1.8: Here is Pair.java: How to fix this error? Is there an elegant way to implement the Cartesian product of several collectio…
Java 8 filter with method call
I am learning Java 8 lambda and streams and trying some examples. But facing problem with it. here is my code Am getting compilation error in .map addr(second argument) field. what wrong in it and could you please provide links to learn java 8 streams. FYI am following this link Java 8 lambda Answer The first…
Why does Stream.allMatch() return true for an empty stream?
My colleague and I had a bug that was due to our assumption that an empty stream calling allMatch() would return false. Of course, it is kind of our fault for assuming and not reading documentation. But what I don’t understand is why the default allMatch() behavior for an empty stream returns true. What…
How to sum a list of integers with java streams?
I want to sum a list of Integers. It works as follows, but the syntax does not feel right. Could the code be optimized? Answer This will work, but the i -> i is doing some automatic unboxing which is why it “feels” strange. mapToInt converts the stream to an IntStream “of primitive int-va…
Idiomatic way to create a Stream from a Nullable object
What is the best/idiomatic way of performing a null-check before generating a stream? I have a method that receives a List that might be null. So I can’t just call stream() on the value that is passed. Is there some static helper in that would give me an empty stream if a value is null? Answer I agree w…
Any way to stream a map like “(k,v)” instead of working with (entry)?
Basically I look for a way to avoid working with and similar to what Map.forEach() does. If only I could get a way to work as map.stream().filter((k,v) -> )… and so on It seems the interface is called BiConsumer. Perhaps with a converter to BiConsumer or a Stream.generate() someway Answer Since this …
How do I keep the iteration order of a List when using Collections.toMap() on a stream?
I am creating a Map from a List as follows: I want to keep the same iteration order as was in the List. How can I create a LinkedHashMap using the Collectors.toMap() methods? Answer The 2-parameter version of Collectors.toMap() uses a HashMap: To use the 4-parameter version, you can replace: with: Or to make …