Forem: Roel Tombozafy

Kotlin fundamentals Part II: conditions

Roel Tombozafy — Fri, 17 Mar 2023 06:32:58 +0000

When you write your code, sometimes you need to check any conditions in order to change the value of a variable or something else. Like other programming language, Kotlin supports conditions with the if instruction

Let's imagine that in our code, we ask the user to input his age. Based on the age, we will display a message: if age is greater than 18 then we output "Adult", if not "Teenager"

prtint("Enter your age: ")
val age = readLine()

if (age > 18) {
    println("Adult")
} else {
    println("Teenager")
}

Sometimes we need to check more than one condition, in that case we use the if else instruction

println("Enter a country code: ")
val countryCode = readLine()

if (countryCode == "MG") {
    println("Madagascar")
} else if (countryCode == "US") {
    println("United States")
} else {
    println("Unknown country")
}

Evaluate multiple values with when

Suppose that we assign a variable capital based on the value of country, we can use if statement to do that but in this case we are a testing the same value multiple times. We'd better use when

val capital: String? // the variable can be null

when(country) {
    "Madagascar" -> capital = "Antananarivo"
    "Spain" -> capital = "Madrid"
    else -> capital = "Unknown"
}

The code above can be written as

// we directly store the return value of when in a variable
val capital = when(country) {
    "Madagascar" -> "Antananarivo"
    "Spain" -> "Madrid"
    else -> "Unknown"
}

In some case we may check for a multiple value in the when statement

when(country) {
    "France", "Spain", "Germany" -> println("Europe")
    "Ghana", "Mali", "Egypt" -> println("Africa")
    else -> println("Somewhere else")
}

We can also use range in the when statement

val number = 42
when (number) {
    in 1..39 -> println("Not yet")
    in 40..45 -> println("Close enough")
    else -> println("Out of range")
}

If there are mutiple statements to execute when a certain conidition is matched, we can use the braces {}

val number = 42
when (number) {
    in 1..39 -> println("Not yet")
    in 40..45 -> println("Close enough")
    else -> { println("Out of range")
              println("Definitely not")
            }
}

That's all for today's article. See you in the next where we are going to talk about functions in kotlin.

Kotlin fundamentals Part I: variables & constants

Roel Tombozafy — Sun, 12 Mar 2023 14:13:58 +0000

Variables are the building blocks to know when you learn a new programming language. In today's article we are going to talk about variables in Kotlin.

Declaring variables: val and var

To declare a variable in Kotlin we use the keyword val or var. If declared with val, a variable is immutable. It means that once set the value of that variable can't be changed throughout the execution of the program. On the other hand, if a variable is declared with the keyword var, its value can change during the execution of the program.

val age = 18 // value can't change
var name = "Lionel Messi"

When using the val keyword to declare a variable, you must set the initial value for that variable.

Kotlin is a statically typed language which means that every variable should have a specific type. To specify a type when declaring a variable, you put a semicolon and the type after the variable name

val age: Int = 18
val salary: Double = 3500.5
var name: String = "David"
var isAdmin: Boolean = false

Kotlin has built-in types like other programming language:

Int for integers
Double for floating numbers
Boolean for boolean value
String for text

Although, you are not forced to specify the variable type thanks to a mechanism called "type inference". It means that Kotlin can infer (or simply guess ) the type of the variable

val country = "Madagascar"

In the example, Kotlin will assume the the variable country is a String due to the presence of the double quotes

Define a constant

To define a constant in Kotlin you need to define a dedicated class and a companion object inside the class

class Constants {
    companion object {
        const val NUMBER_OF_DAYS_IN_YEAR = 365
    }
}

To use that constant in your code, you need to import it like shown in the example below

import Constants.Companion.NUMBER_OF_DAYS_IN_YEAR
fun main() {
    println("One year has $NUMBER_OF_DAYS_IN_YEAR")
}

Working with String

To create a string you can call the String constructor and assign it to a variable

val myString = String()

Or by assigning a value when creating the variable

val myString = "Hello Kotlin"

To get the length of a string, use the length property

val myString = "Kotlin"
myString.length

Many methods are available for string manipulation

val myString = "Hello World"
myString.uppercase() // "HELLO WORLD"
val position = myString.indexOf("W") // 7
myString.substring(position) // "World"

Like in Java, you can build a string using the StringBuilder class

var builder = StringBuilder("Hello EveryOne ")
    builder.append("Kotlin is cool")

It will create the string "Hello EveryOne. Kotlin is cool"

That's all for today. See you in my next article

Dart Fundamentals: Variables

Roel Tombozafy — Sat, 11 Feb 2023 14:28:33 +0000

Variables are the building blocks to know when you learn a new programming language. In today's article we are going to talk about variables in Dart.

Dart has built-in types like other programming language:

int for integers
double for floating numbers
boolean for boolean value
String for text

To declare a variable in Dart, we define the variable type followed by the variable name

int currentYear = 2023;
double pi = 3.14;
bool isAdult = true;
String name = "Lionel Messi"

Type inference: var & dynamic

Although, you are not forced to specify the variable type thanks to a mechanism called "type inference". It means that Dart can infer (or simply guess) the type of the variable

var myAge = 27;
var country = "Madagascar"

In the example above, Dart will assume that the variable myAge is an integer and the variable country is a string due to the presence of the double quotes. When declared with the var keyword, the type of the variable can't be changed throughout the execution of the program.

The dynamic keyword can also be used to declare a variable. The difference with var is that the type of the variable can change during the execution of the code.

dynamic myVar = "Hello"
print(myVar.runtimeType) // String 
myVar = 123
print(myVar.runtimeType) // int

The important thing to remember is:

var can't change the TYPE of the variable, but can change the VALUE of the variable later in code
dynamic can change the TYPE of the variable and can change the VALUE of the variable later in code
final can’t change TYPE of the variable, and can’t change VALUE of the variable later in code.

For example

var myVar = "Hello"
dynamic myDynamicVar = "Hello"
myVar = 123 // not possible
myDynamicVar = 123 // possible

Note: If you state a var without intializing, it becomes a dynamic

var myVar;
myVar = "abc";
print(myVar.runtimeType) // String
myVar = 1245;
print(myVar) //1245
print(myVar.runtimeType) // int

That's all for today's article. If you want to deep dive into the fundamentals of Dart, check out the official documentation.

The “essential” ingredient to become a good developer

Roel Tombozafy — Tue, 07 Feb 2023 12:09:08 +0000

It was a December 03, 2015. Finally, after more than a year of waiting Swift is now opensource. Curious and motivated by the idea of discovering this new language, I went to the official swift.org website. Baaaammmm !!! Big rant: all the documentation is in English. No French version in sight...

Somewhat frustrated with the situation, I still managed to get Swift running on my machine. At this precise moment I realized the need to speak or at least understand the language of Shakespeare for a developer.

Why should the English language be part of the developer's artillery?

Good question but not easy to answer. In a single sentence I would say: “The higher your level of English, the more serene and advantaged you will be”

If I had to classify the English level of a developer, I would say that there are 3 levels:

level 1: reading only: you know how to read and understand English: this is already a good thing. Almost all the online documentation is in English, it will be a bit complicated for you to implement an API whose doc is entirely in English if you are Anglophobic :)
level 2: reading and writing only: you know how to interact at least in writing. It's also a big step: you can contribute to opensource projects on github. In case of problem, you can even ask for help on stackoverflow, isn't that good? :)
level 3: reading, writing, speaking, listening: at this stage you are ready to conquer the world. Negotiating with an English-speaking client? it's up to you. Watch the Apple keynote live? you are part of it.

To the apprentice-developers, or to those who are already, you are already code warriors, I have no doubt about it. You master good practices and everything that goes with it, I'm sure. Just always try to improve in English, it will help you in the future.