Lessons

Sergey is a professional boxer from Chisinau, whose life was radically changed by a sports injury. Once upon a time, he decided to share his success story, or rather, to relate how you can recover from a blow of fate and build a new career in a completely different field. We hope this story will be motivation...

Java classes whose main purpose is to store a set of other elements are called collections or containers. It makes sense that something we collect is called a collection. Java collections are divided into three main groups: Set, List, Map (or dictionary). This lesson will teach you the difference between them.

Even the very first quest at the secret CodeGym center deals with important matters, so of course the eighth level does. Let's continue getting to know a serious tool: collections and collection interfaces. In this lesson, you will learn that Java has four Lists, three Sets, and four Maps. You'll study a few examples to deepen your understanding.

Have you ever collected cats? What about plants? Can you guess what HashMap means without any hints? Too many questions! But if you said 'yes' to at least two of the three question, then it's time to create cats and add them to a collection! We'll do tasks involving collections, simultaneously creating a HashSet of plants and a HashMap of cats.

An interface can have multiple implementations. No single implementation is always better than the rest. In one approach, some operations are fast, but others are slow. The opposite can be true for another approach. That's why the List interface has two different classes: ArrayList and LinkedList. This lesson explores how one is better than the other and vice versa.

The topic of "collections" can fry your brain, but we'll try to train your brain to make the smoke point as high as possible... So let's work on some tasks, preferably interesting ones. Let's take some measurements right in this lesson: We'll find out how long it takes to perform 10,000 insertions on each of the lists, and how long it takes to call get the same number of times.

A Set is a bunch of unnumbered objects. A Map is a set of key-value pairs. Though they are similar, but there are some things you can do with Map that you can't do with Set. In the latter case, we just add elements, delete them, and check if they are in the set. But a Map supports many more operations. Wanna know what these operations are? Let's complete this lesson.

Though not as popular as ubiquitous lists, Map (a set of key-value pairs) is used in many tasks. In this hands-on lesson, you'll learn how to work with Map and Set in the standard CodeGym way. Have you guessed the way*? (*answer: by completing tasks).

In this level, you continued to get acquainted with collections: you figured out what HashMap and HashSet are, and also learned more about the methods of the Collections helper class. In the context of HashSet, it was relevant to talk about another type of loop: the for-each loop, which will help you display a list of HashSet elements...

Several tasks must be completed at the end of the level. Some of them are more advanced and require student's to be able to google. Or think. Or think and google. Practice completing them day in and day out, and your skills will grow at an incredible speed. They were created especially for IDEA.