The use of lambdas in the video

Hi noob developer. I don't know if you've figured this out since then but in case you haven't, I'll give you my understanding of things. I'm new to Functional programming too but from what I understand, the common denominator here is the functional interface (@FunctionalInterface).

Let's first look at the exercise from the Lambda workshop. We have a sort() method that takes a Comparator interface as one of the arguments. We can use an anonymous inline class:

public static void usingAnonymousInlineClass() {
  List<Book> books = Books.all();
  Collections.sort(books, new Comparator<Book>() {
      @Override
      public int compare(Book b1, Book b2) {
          return b1.getTitle().compareTo(b2.getTitle());
      }
  });

  for (Book book : books) {
      System.out.println(book);
  }
}

Looking at the documentation, Comparator is, in fact, a functional interface (you can see the @FunctionalInterface annotation), meaning it only has a Single Abstract Method (SAM), compare(), that we are overriding. Now, every time we have to use a functional interface, we can actually use a lambda instead. So, we now get:

public static void usingLambdasInShortForm() {
  List<Book> books = Books.all();

  Collections.sort(books, (b1, b2) -> b1.getTitle().compareTo(b2.getTitle()));

  books.forEach(book -> System.out.println(book));
}

In this lesson's exercise, setOnAction() also takes an interface as an argument, EventHandler, which also happens to be a functional interface in JavaFX, its single abstract method being handle(). We could write it using an inline anonymous class:

Button btn;
  btn.setOnAction(new EventHandler<MouseEvent>() {   // not sure about the MouseEvent type here. just a guess
    @Override
    public void handle(Event event) {
      System.out.println("Sup was clicked"));
    }
  });

But because it's a functional interface, we can simplify it with a lambda:

btn.setOnAction(evt -> System.out.println("Sup was clicked"));

Lambdas do shorten the code and makes the syntax easier to read, especially when you can go one step further and use method references .

I hope that helps :)