About This Series
This “Android Kotlin Basics” blog series is all about fundamentals. We’ll take a look at the basics of building Android apps with Kotlin from the SUPER basics, to the standard basics, to the not-so-basics. We’ll also be drawing comparisons to how things are done in Kotlin vs. Java and some other programming languages to build Android apps (like C# and Xamarin or JavaScript/TypeScript for Hybrid implementations).
Check Out the Pluralsight Course!
If you like this series, be sure to check out my course on Pluralsight – Building Android Apps with Kotlin: Getting Started where you can learn more while building your own real-world application in Kotlin along the way. You can also join the conversation and test your knowledge throughout the course with learning checks through each module!
Watch it here: https://app.pluralsight.com/library/courses/building-android-apps-kotlin-getting-started/table-of-contents
Kotlin Property Encapsulation
Okay, let’s get to it then. Kotlin is an object-oriented, statically typed, programming language. This means we use interfaces, classes, and abstract classes (among some other unique data structures) to define our data and objects. Encapsulation in our classes serves 2 primary purposes – Code security and architecture strength. It’s how we restrict access to these data structures as well as their contained properties and functions.
In this post we will focus on how we encapsulate properties within our classes, interfaces, and more. Kotlin is 100% interoperable with Java so its practices have to work back and forth with the limitations of Java as well. Let’s take a look at ways we encapsulate properties in Java first, then show how much better it is in Kotlin!
Let’s look at 2 classes – Animal and a child class Dog. We’ll first be showing the Java implementation, then look at how much nicer the Kotlin implementation is!
Animal.java
abstract class Animal {
// name property
private String name;
// constructor with name parameter
protected Animal(String name) {
this.name = name; // sets the name
}
public String getName() {
return this.Name
}
public void setName(String name) {
this.name = name;
}
}
Dog.java
public class Dog extends Animal {
private String breed;
// constructor with name parameter
protected Dog(String name, String breed) {
super(name); // sets the name through base constructor
this.breed = breed;
}
public String getBreed() {
return this.breed;
}
}
To summarize the relationship – Animal has a property called name that we have access to both get and set via the getName and setName functions. Dog then inherits those functions from the Animal class and adds a new property called breed, but breed can only be set by the constructor, so we do not create a setBreed function.
This is just a simple example of encapsulating properties and using functions to manage the access of reading and writing the data separately.
Now let’s see how much better this looks in Kotlin:
Animal.kt
abstract class Animal(public var name: String) { }
Yup… that’s literally it. This creates an abstract class with a public property name that is instantiated in the constructor and has public access to both read and write.
Now let’s look at how that inheritance works and how to restrict write access
Dog.kt
class Dog(name: String, breed: String) : Animal(name) {
val breed: String = breed
private set
}
4 lines of code. A class that inherits everything from Animal and has a breed property that is set by the default constructor and can only be set privately.
You can use these get and set modifiers to restrict access to either as well as create custom “dynamic” getters and setters (that we will look at further later in the series).
There are many different ways to handle the code above in Kotlin, but I wanted to demonstrate the shortest and most direct. In future parts of the series, we will also look at constructor overloading, dynamic getters/setters, val vs. var, and so much more.
One last thing – because Kotlin is interoperable with Java, we need to know how this ends up outputting in Java. When we create custom getters and setters for public properties, it actually creates a dynamic function getPropertyName and setPropertyName that can be consumed by Java. And even does it the other way around. If you reference a Java library in your Kotlin code, you can access the underlying property since it will automatically map methods with the prefix of “get” or “set” to custom properties. Pretty cool!
For those coming from a C# background this is extremely similar to how C# handles property getters and setters. In C# it will create methods with the name get_PropertyName and set_PropertyName to handle the dynamic encapsulation and implementations! Kotlin pulls the best parts from the best langauges!
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Alex Dunn 