Lessons

Java's strict typing does not allow data types to be changed. However, there is a way. It's called type casting. And we're not talking about an actor being locked into a particular role. In this context, we mean something else — using assignment to converting a variable of one type to a variable of another type. You'll learn how this happens in Java in this lesson.

The topic of type conversion must be approached responsibly: for many CodeGym students, it seems simple (still, it's Level 10!), but a flippant attitude here leads to numerous programming errors even for "grown up" programmers. So let's build a habit of approaching type conversion correctly. How? By doing tasks, of course.

Despite Java's strict approach of typing, you can turn any data type into a String! Moreover, almost every type can be cast to the String type implicitly. This is immediately evident if we try to add two variables: a String and a "non-String". In this case, the "non-String" variable is converted to a String. It's convenient. Let's learn how to use it!

When compatibles types are converted, the conversion may be narrowing or widening. Today, we'll use the Object class as we look at type conversions. Any reference type can be assigned to such a variable (type narrowing). But what if you need to perform a widening conversion? You'll learn in the lesson.

The first quest is coming to an end! This crucial moment is the best time to repeat the material and reinforce your knowledge through practice. Accordingly, in this block we have prepared tasks on various topics, and even several problems that are more advanced. If something isn't clear, you can google it. Think and google, got it? Good luck!

Does a math degree give an edge when learning programming? Everything depends on how much effort you put into related subjects. This is the story of Roman, who is from Kharkov. Today he is a senior Java developer. In mid-2015, he was a student working on a master's degree in applied...

For a beginner, the ArrayList class is aerobatics! This topic usually comes much later, but here at the secret CodeGym center we decided not to drag out the Cat cat = new Cat() by the tail. So we created an overview of ArrayLists for the very first quest. Here we'll try to explain what kind of class ArrayList is and compare it with ordinary arrays.

We're strictly adhering to the methodology adopted by the secret CodeGym training center: learn information and then practice using it. The now incomprehensible and complex phrase ArrayList<String> list = new ArrayList<>() will soon become instinctive and clear. As plain as «Hello, I'm a list of strings. You can call me 'list'».

According to Wikipedia, a generic is a drug sold under an international non-proprietary name or under a proprietary name different from the brand name. In Java, generics… Uh...are in no way related to generic drugs. They're just types with a parameter.

You will be fully immersed in Java generics and ArrayList during your second quest at the secret CodeGym center. But right now we'll slow become accustomed to these complex but essential structures, analyzing code snippets with detailed explanations from your teachers.

According to research performed by the secret CodeGym center in academic year 3099, ArrayList appears to be the most difficult topic for the students working on the first quest. One of... So don't idle your time away: take the bull by the horns and start completing tasks. The more tasks you do, the clearer ArrayList will become.

You already know a lot about primitive types, and in this level you got acquainted with their doppelgangers — the wrapper classes, and learned what autoboxing and unboxing are, how to compare wrapper types correctly, and how to do it incorrectly. You also took your array experience to the next level by getting to know...