Lessons

Reference variables. In the Java language, there are two kinds of variables: primitive variables and everything else. As it happens, we're going to talk about "everything else" now. In fact, it would be more correct to say that there are primitive variables and reference...

Objects. Everything in Java is an object. More accurately, there are very few things in Java that are not objects. For example, primitive types. But this is a rather rare exception to the rule. So what is an object? An object is an entity that groups data together with methods that process the data. When we say...

To understand what null means in Java, let's look at an analogy with numbers: the number 0 symbolizes the absence of something, and null means the same thing when it comes to reference data types.

Introducing the principles of OOP. Today you will discover a new and interesting world. The world of Object-Oriented Programming (OOP). You previously learned about classes and objects. Today you will learn more about them, much more. OOP emerged as a response to the increasing...

Company history. I want to tell you a story that demonstrates how OOP helps fight with the complexity of large systems. This is necessary for you to understand the purpose of OOP. Once upon a time there was a small company that provided intergalactic shipping services... Let's call it Galaxy Rush. It employed...

Pegasus. Let's take a deeper look at the third principle of OOP: inheritance. This is a very interesting topic that you will use quite often. To the uninitiated, programming is indistinguishable from magic. So let's start with an interesting analogy... Let's say you are a wizard who wants to create a flying...

Objects and classes. Today you'll learn a little about how a typical Java program works. Here's the big news: every Java program consists of classes and objects. You already know what classes are, but what are objects? I'll start with an analogy. Imagine you want to make a small ship.

Creating an object. Well, we've arrived at creating objects. You already encountered this before, but now we will analyze this topic in more detail. It's actually very easy to create objects. To create an object, you need to use the new operator. Creating an object looks approximately like this: new Class...

Initializing variables. As you already know, you can declare several variables in your class, and not just declare them, but also immediately initialize them with their starting values. And these same variables can be initialized in a constructor as well. This means that, in theory, these...

Properties: getters and setters. When a large project is being developed by dozens of programmers at the same time, problems often crop up if they handle the data stored in class fields differently. Maybe people fail to study the class documentation in detail, or perhaps it doesn't describe every...

Comparing objects in Java. In Java, objects can be compared both by reference and by value. Comparing references. If two variables point to the same object in memory, then the references stored in these variables are equal. If you compare these variables using the equality operator (==)...

The best way to internalize theory is to practice it. If this topic seemed difficult to you, we recommend solving extra tasks in order to help you fill in the gaps in your knowledge. Or if the few required tasks are enough for you, feel free to move on to the next...