1. Why Kotlin for Android?

This is the first milestone towards our Kotlin series.

why kotlin?

What is Kotlin?

Kotlin is a statically typed programming language for building modern, multi-platform applications.

It was launched in 2011 by JetBrains.

Why Kotlin?

• Open source: Under Apache 2.0 so it will evolve tremendously backed by JetBrains and now Google.
• Compatibility: Kotlin is fully compatible with JDK 6, ensuring that Kotlin applications can run on older Android devices with no issues.
• Performance: A Kotlin application runs as fast as an equivalent Java one, thanks to very similar bytecode structure.
• Interoperability: Kotlin is 100% interoperable with Java, allowing to use all existing Android libraries in a Kotlin application..
• Learning Curve: For a Java developer, getting started with Kotlin is very easy.
• Support: Kotlin is fully integrated in Android Studio 3.0 and before that we could use Kotlin plugin to use in Android Studio.

Why you should totally switch to Kotlin

What are the Basic Syntax?

1. No more Semi;colon;
2. Variable declaration: Can be either var (read/write) or val (read only). There is no primitive types in Kotlin. We use “Double”, “Int” etc instead.

val a: Int = 1 // immediate assignment
val b = 2 // `Int` type is inferred
val c: Int // Type required when no initializer is provided
c = 3 // deferred assignment
val oneMillion = 1_000_000 // Can use underscores for readability

2. Defining functions: Functions can be defined by fun keyword.

// Function with params and return type
fun sum(a: Int, b: Int): Int {
 return a + b
}
// Function with params and no-return type
fun printSum(a: Int, b: Int) {
    println("sum of $a and $b is ${a + b}")
}

3. Using conditionals: Pretty much similar to all the languages except notable for switch statements which is done by when statements. Break and Continue are supported similarly as well.

// for loop
for (item in collection) print(item)
// while loop
val items = listOf("apple", "banana", "kiwi")
var index = 0
while (index < items.size) {
    println("item at $index is ${items[index]}")
    index++
}
// switch statements is replaced by when
private fun gettSuit(i: Int): String = when (i / 13) {
    0 -> "Clubs"
    1 -> "Diamonds"
    2 -> "Hearts"
    else -> "Spades"
}

4. Null Safety (The Billion Dollar mistake fix): In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references).

Using safe call operator (?)

private var number: Int? = null // Here we are telling compiler that number can have null value. By, default any variable cannot be null in kotlin.

Using the not-null assertion operator (!!).

This option is for NPE-lovers. If we want an NPE, we can have it, but you have to ask for it explicitly using (!!), and it does not appear out of the blue.

val l = b!!.length // converts any value to a non-null type and throws an exception if the value is null

Checking for null with Elvis Operator.

val l: Int = if (b != null) b.length else -1 // Null-value check with if-expression
val l = b?.length ?: -1 // We can use Elvis Operator instead of if-expression

Safe Casts. Regular casts may result into a ClassCastException if the object is not of the target type.

val aInt: Int? = a as? Int // Using safe casts will return null if the attempt was not successful

Function that returns null. Marking the return type with (?) as nullable when null value is possible.

// Return null if str does not hold an integer:
fun parseInt(str: String): Int? { 
    // … 
}

5. Using Collections:

// Iterating over a collection
for (item in items) {
     println(item)
}

6. Creating instance of classes:

val rectangle = Rectangle(5.0, 2.0) //no ‘new’ keyword required
val triangle = Triangle(3.0, 4.0, 5.0)

7. Conditional if expressions: In Kotlin, if is an expression, i.e. it returns a value. Therefore there is no ternary operator (condition ? then : else), because ordinary if works fine in this role.

fun maxOf(a: Int, b: Int) = if (a > b) a else b

Basic Syntax — Kotlin Programming Language

The Second milestone in this series.

2. Hello Kotlin

2. Hello Kotlin

References:

1. Using Kotlin for Android development ~ Kotlin.org
2. Resources to Learn Kotlin ~ developer.android
3. Why switch to Kotlin? ~ Medium blog
4. Variable types in Kotlin ~ Kotlin.org