Streams can be filtered, mapped, collected… — There is also the possibility to loop over the stream elements to perform some logic. All in the one-line-of-code style, typical of functional programming. Bear with me and let’s try to perform an operation over each element of our list of users. Let’s use the .forEach() method. Now, the…

When lists of lists meet streams — .flatMap() is one hell of a tool. It needs a little attention at first but opens the gate to real problem-solving. Let’s update our User class and provide each user with a list: Without the need of specifying what the Document class is. If we work with a…

The Final Cut — — Dad? C’mon! Wake Up! You told me I could have my present this morning! That’s when things started going shit. I was six, it was Christmas morning and I was intrepidly looking forward to opening my present. — Mom! Dad won’t wake up! I ran to my mom, she…

I was there to score — One day I found Naydia, on Facebook. She had a sweet face, kind eyes and a shy smile in her profile picture. Not really my type but I was not there to choose. I was there to score. She was my age, an off-site medical student recently in my city…

If you want to get rid of duplicate elements in a collection, a stream intermediate operation comes in help. Let’s resume our evergreen example of the list of users. The Java 8 Stream API provides a useful intermediate operation: distinct() . The usage is extremely simple but requires some…

Trick your Mind, never been so easily — The trick is to make a to-do list. A simple, trivial to-do list. I discovered this by pure chance during my freshman year at University. Things were not going my way. I felt overwhelmed, stagnant, and paralyzed. Scared and anxious. It seemed that the few things I had to do…

I was so excited when I turned the key in the lock, as silently as I could. Still like a stone, but hopping like a bunny inside. I ditched school and took four bus trips to reach my boyfriend’s apartment. I wanted to surprise him after his first night shift. …

From a Stream, a Map. of Lists — We found that collecting a stream to a map is not completely safe, here in this article: Java Streams: Collect a Stream to Map From a Stream, a Map.danio-quero.medium.com I also said that two possible solutions came to my mind, here is the first one. When collecting to a map, if the keyMapper finds a non-unique key an exception is thrown, saying…

From a Stream, a Map. — We already had a glimpse at the Collectors class when we needed to turn a stream back into a list, with the Collectors.ToList() static method here: Java Streams: Filters Filter out elements using lambda and predicatesmedium.com Powerful and easy, it returns a list of the same type as the original stream. Collectors allows also some other interesting trick, for example…