Lessons

Once upon a time there were InputStream and OutputStream. They are declared as abstract classes. But if you look closely, they're quite real interfaces. Almost all of their methods are abstract, except for a few insignificant methods. So, here's the question: What makes them special? And why did they make them abstract classes anyway?

Captain Squirrels is on the phone! He has a couple of surprises for you. More precisely, not a couple, and they aren't surprises, but rather ten tasks to reinforce your knowledge of abstract classes and interfaces. And the truly curious can try their hand on three bonus tasks. You'll really have to put on your thinking cap to complete these tasks.

In this lesson, we'll talk about an important concept in Java: interfaces. You're probably familiar with the word. For example, interfaces...

"Hi, Amigo!" "Hi, Ellie!""Today, Rishi and I are going to tell you all about generics." "Wait, I think I already know almost everything." "Almost everything, but not everything." "Really? OK, I'm ready to listen." "Then let's begin ..."

"Now for a new, interesting topic: wildcards." "Essentially, this is something like a «*» pattern that matches anything." "But let's start from the beginning." "Imagine that you have a Warrior class and a method that determines which of two warriors is stronger. Here's how this might look ..."

"Hi! I'm going to continue Ellie's lesson on generics. Ready to listen?" "Yes." "Then let's begin." "The first thing you need to know is that a class's methods can also have their own type parameters." "I know." "No, I specifically mean their own type parameters ..."

"Well, finally — another small lesson on generics." "Now I'm going to tell you how to get around type erasure." "Ah. That's something I want to know." "As you probably already know, Java has a Class type, which is used to store a reference to an object's class. "Here are some examples ..."

Additional lessons for the level

Interfaces. To understand what lambda functions are, you first need to understand what interfaces are. You will learn about interfaces in Levels 1 and 2 of the OOP quest. That said, we can briefly summarize this material now, which will greatly facilitate your understanding later. An interface is a variation...

Functional methods. If an interface has only one method, a variable of that interface type can be assigned a value given by a lambda expression (lambda function). Such interfaces became known as functional interfaces (after Java added support for lambda functions). For example, Java...

Innovations in Java 8: Functional programming. With the release of Java 8, the language gained powerful support for functional programming. I could even say it gained long-awaited support for functional programming. Coding became faster, although the code was more difficult to read 🙂 Before learning...

List of methods of the Stream class. The Stream class was created to make it easy to construct chains of data streams. To achieve this, the Stream<T> class has methods that return new Stream objects. Each of these data streams does one simple action, but...