Kotlin is a modern and concise programming language that is widely used for developing Android applications. Sealed classes are one of the unique features of Kotlin that make it a powerful tool for writing robust and maintainable code. In this tutorial, we will learn about sealed classes in Kotlin, their benefits, and how to use them effectively.
What are Sealed Classes?
Sealed classes are a special type of class in Kotlin that restricts the inheritance of classes to a specific set of subclasses. This makes it easier to define and maintain the structure of your code.
Why use Sealed Classes? The use of sealed classes provides several benefits over traditional inheritance, including:
Improved type safety: With sealed classes, you can limit the number of subclasses that can inherit from a parent class, making it easier to maintain the structure of your code and prevent bugs.
Better code readability: Sealed classes make it easier to understand the relationships between different classes and their subclasses, making it easier to understand the code.
Better code maintenance: Sealed classes make it easier to maintain and refactor your code, as it is easier to see how the different parts of your code relate to each other.
How to use Sealed Classes in Kotlin?
Sealed classes are defined in Kotlin by using the keyword "sealed" in front of the class declaration. Here is a simple example of a sealed class in Kotlin:
sealed class Shape { class Circle(val radius: Double): Shape()
class Rectangle(val width: Double, val height: Double): Shape()
class Triangle(val base: Double, val height: Double): Shape() }
In this example, the class "Shape" is a sealed class, and it has three subclasses, "Circle", "Rectangle", and "Triangle".
These subclasses are the only subclasses that can inherit from the "Shape" class.
To use a sealed class in your code, you can use a when expression to check the type of an object and take different actions based on the type. For example:
fun calculateArea(shape: Shape) = when (shape) {
is Shape.Circle -> Math.PI * shape.radius * shape.radius is Shape.Rectangle -> shape.width * shape.height is Shape.Triangle -> 0.5 * shape.base * shape.height
}
In this example, the function "calculateArea" takes a "Shape" object as its argument, and uses a when expression to calculate the area of the shape based on its type.
some more points to consider when using sealed classes in Kotlin:
Sealed classes are open by default: Unlike regular classes, sealed classes are open by default, which means that they can be extended by subclasses. However, the subclasses must be defined within the same file as the sealed class, or in a file that is marked as a companion object.
Sealed classes can have properties and methods: Sealed classes are not limited to just being a container for subclasses, they can also have properties and methods of their own. For example, you could add a property to the "Shape" class that defines the color of the shape, and a method that returns the name of the shape.
Sealed classes can be used as the basis for data classes: Sealed classes can be used as the basis for data classes, which are classes that are used to store data. This allows you to create complex data structures with a clear and concise structure, which makes it easier to work with the data in your code.
Sealed classes can be used to define a closed hierarchy: With sealed classes, you can define a closed hierarchy of classes, which means that you can limit the number of subclasses that can inherit from a parent class. This makes it easier to maintain the structure of your code, as you can be sure that only the intended subclasses will inherit from a parent class.
Sealed classes are useful for defining type-safe enums: Sealed classes are particularly useful for defining type-safe enums, which are a way of defining a set of values in a type-safe way. With sealed classes, you can define a set of subclasses that represent the different values, and then use a when expression to handle each value in a type-safe way.
In conclusion, sealed classes are a valuable tool in the Kotlin developer's toolbox. By using sealed classes, you can improve the structure, readability, and maintainability of your code, and create complex data structures in a clear and concise way.
Hope you understand the sealed classes in the next blog we are going to learn Data classes in kotlin.
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