Welcome! Today, we're delving into Kotlin variables, which are critical elements in any programming language. They function as containers that store and handle data. In this lesson, we will explore what they are, learn about assigning values and assigning names to them, and discuss what constants are in Kotlin.
A variable is a slot in memory that stores data, its content can change during the execution of the program. For example, in the snippet below, the value "Alice" held by myName is replaced by "Bob":
Kotlin1var myName = "Alice" 2println(myName) // Output: Alice 3 4myName = "Bob" 5println(myName) // Output: Bob
Kotlin has two types of variables - val, which is immutable, and var, which is mutable.
In Kotlin, you can reassign values to variables declared with var, but variables declared with val are immutable. Let's assign and reassign a value to myAge to see this in action:
Kotlin1var myAge = 25 2println(myAge) // Outputs: 25 3 4myAge = 30 5println(myAge) // Outputs: 30
Now, let's try to alter a constant, myBirthYear:
Kotlin1val myBirthYear = 1991 2println(myBirthYear) // Outputs: 1991 3 4myBirthYear = 1990 // Error: Val cannot be reassigned
In Kotlin, we adhere to the camelCase naming convention, which helps deliver clear, purposeful names. Good examples include numberOfStudents, accountBalance, userDetails. Poor examples like c, xyz, temp lack clear purpose and should, therefore, be avoided.
Kotlin uses const val for constants, which are declared at the top level:
Kotlin1const val PI = 3.14159 2println(PI) // Outputs: 3.14159 3 4PI = 3.15 // Error: Val cannot be reassigned
Constants are used for values that are not subject to change.
In Kotlin, you can incorporate variable values into a string using a technique called string interpolation. This technique makes your code more concise and easy to read. Here's an example:
Kotlin1fun main() { 2 val name = "Kotlin learner" 3 val topicsCovered = 2 4 println("Hello, $name! You've covered $topicsCovered topics today") // prints "Hello, Kotlin learner! You've covered 2 topics today" 5}
In the code snippet above, $name and $topicsCovered within the quotes act as placeholders. Kotlin automatically substitutes them with the values of the name and topicsCovered variables when the code executes.
Let's construct a simple program that applies the concepts we've learned:
Kotlin1var userName = "Alice" 2val userAge = 25 3 4println("User Details: ") 5println("Name: $userName") // prints "Name: Alice" 6println("Age: $userAge") // prints "Age: 25"
The main takeaway here is the utility of variables in storing and manipulating data in Kotlin.
Congratulations! You've learned all about Kotlin variables, including their declaration, naming conventions, assignment operations, and constants. Next up, we have exercises to help reinforce your new knowledge. Remember, practice is key to mastering any concept, so dive in with enthusiasm! Happy coding in Kotlin!