Welcome back, Kotlin enthusiasts! Today, we're diving into Kotlin classes, focusing on primary constructors and class methods. Imagine you're building a robot: Constructors determine its initial setup, while methods are the commands that let it perform actions. Ready to start constructing? Let's dive in!

A Kotlin class acts as a blueprint for creating objects. Here's a basic class, Robot:

This Robot class is currently an empty shell — it exists, but it hasn't been given any properties or behavior yet. To make it functional, we need to introduce properties and methods.

In Kotlin, the primary constructor is part of the class header. It helps initialize an object when it's created. We can define properties directly within this constructor.

Here's how we can enhance the Robot class with a primary constructor:

In this example, the primary constructor takes name and color as parameters, which serve to initialize the properties for every new Robot instance. This ensures that each instance starts with the correct initial values.

Properties can also be defined inside the class body:

This approach is useful when you want to add properties that don't need to be initialized through the constructor.

Having a single constructor is useful, but what if we want more flexibility in setting up our robots, such as providing default values? Kotlin allows us to define default values for parameters, which achieves the same effect.

Let's set a default color for our robots:

With default parameters, providing a color is optional. If it's not specified during the creation of a robot, it defaults to 'grey'.

We can also use init blocks to run code during instance creation:

The init block is executed during instance creation, right after the primary constructor. It's useful when you need to run some initialization logic.

Class methods are the commands that dictate behavior for our objects. Here's how we can make our Robot introduce itself in Kotlin:

The sayHello method allows each Robot instance to interact and communicate its identity.

Great job! You've explored and deepened your understanding of Kotlin classes, primary constructors, and class methods. By utilizing Kotlin's primary constructors and default parameters, you've learned how to build more versatile and dynamic classes, much like constructing interactive and adaptable robots. Keep up the great work, as these concepts will empower you to create more complex applications efficiently.