Kotlin Geek Series 🤓

Let’s get down to the nitty-gritty of Kotlin

Episode 1 - Basic Types

We are heading to an exploration journey toward those nitty-gritty Kotlin details that may win you a T-shirt on a programming conference’s victorine or grant you a highly paid job, who knows! (A word of advice: take the T-shirt, money won’t make you happy but an ugly programmer’s tee — for sure!).

What you will learn? Facts about:

• Floating-point types
• Explicit conversions
• Arithmetic operations
• Unsigned integers
• Strings
• Arrays

If you are impatient just check my code at the end of the article. It could be used instead of the article itself.

This article will be organized as a question-answer quiz, cause I know you are smart and won’t bore you with information you already know. Each correct answer gives you one Kotlincoin (yay, you will be a millionaire!)

Floating-point types

• What is the type of this expression?

val pi = 3.14

▶ It is Double. All float point literals are double by default.

• What is the difference between Double and Float?

▶ Double has 15–16 digits, while Float has 6–7.

• What is the actual value of this expression?

val fl = 2.12345678f

▶ It is 2.1234567. If a Float value contains more than 6–7 decimal digits, it will be rounded. In my case it was not rounded but trimmed.

• Can you call a function with Double parameter with a Int or Float value?

▶ No! No implicit widening. You can use only Double.

• Can you write a number as

val oneMillion = 1_000_000

▶ Yes!

• How Kotlin cast Numbers to Java?

▶ Numbers are casted to Java primitives if possible. If type is Int? it is boxed in Java’s Integer .

• Can you compare accurately floating point values like that

3.145 == 3.14 or 3.12 < 42?

▶ Yes! There are equals and compareTo implementations for Float and Double so your comparision is safe and accurate.

• How you can check if number is in certain range?

▶ x in a..b

• How you can check if number is not in certain range?

▶ x !in a..b

Explicit conversions

• Could you cast Byte to Int?

val byte: Byte = 1
val int: Int = byte

▶ No, you need to use byte.toInt()

• What about this expression?

val byte: Byte = 1
val result: Int = 1 + byte

▶ Yes, in an arithmetic operation the cast happen automatically.

Smaller types are NOT implicitly converted to bigger types.

Arithmetic operations

• What is the result?

val x = 5 / 2

▶ It is 2. Two integers return integer, fraction (0.5) is removed.

• How can you return Double?

▶ val x = 5 / 2.toDouble()

Explicitly convert one of the arguments to a floating-point type.

Unsigned integers

• Do we have unsigned integers in Kotlin? Example?

▶ Yes! UByte ranges from 0–255 an unsigned bit integer

val b: UByte = 1u

• Using our pervious knowledge can we do val i: Int = 1u ?

▶ No, you can’t cast Byte to Int explicitly, and you can’t cast an unsigned to signed value either, so it is double NO (No, No)

Booleans

• Can you have nullable Boolean?

▶ Yes. There is Boolean?

Characters

• How do you represent a literal?

▶ Single quote '1'

val char: Char = ‘a’

• Can you take the number value represented by Char and use it in expression? See the example:

val numChar: Char = '9'
val sum = numChar + 1 

▶ Yes. Use digitToInt() Kotlin goody.

val sum = numChar.digitToInt() + 1 // sum will be 10

Strings

• Can you iterate over characters of String?

▶ Yes. Just use a for loop.

val string = "12345567"
for(ch in string){
    print("$ch, ")
}

• Will this create a new String object?

println(str.uppercase()) // Create and print a new String object

▶ Yes. All operations that transform strings return their results in a new String object because String is immutable class.

• How do you concatenate String?

▶ Use + BUT in most cases using string templates or raw strings is preferable to string concatenation.

• Can you concatenate like this:

val s = 1 + "abc"

▶ No, the first element in the expression needs to be String.

String literals

• How do you escape character?

▶ Use backslash “\” .

• How do you escape a whole string?

▶ Use triple quote “”” .

println("""Sentence 1
    Sentence 2 on new line
""")

• How you can remove the empty space around a string?

“ A user entered sentence… “

▶ Use trimIndent() .

val withoutIndent =
    """
        ABC
        123
        456
    """.trimIndent()

• How you can format text on few lines?

▶ Call trimMargin() and use | as margin prefix or set your own character.

String templates

• How you can embed code in a String for example “Hello [value]”?

▶“Hello $name” may print Hello James.

• What about more complex stuffs “Your age is [some date calculations]” ?

▶ Use curly braces if you need expression. “Your age is ${Period.between(bday, now)}” .

• How you can insert the $ character in a raw string?

▶ Use “${‘$’}” .

println("Hello $name. You are ${Period.between(bday, LocalDate.now()).years} years old. You owe me 1${'$'} for this calculation!")

Arrays

• How do you create an array?

val array = arrayOf(3, 4, 5)

• How do you create an array initialized with null?

val arrayNul = arrayOfNulls<Int>(5)

• How do you get or set a value in array?

▶You can use get() and set() methods or overloaded operator []

arrayNul[2] = arrayNul[0]?.plus(arrayNul[1] ?: 1)

• Create array with string numbers from 0 to 4

val asc = Array(5) { i -> i.toString() }

• Is Array<String> assignable to Array<Any>

▶ No, but Array<out Any> is!

val stringArray = arrayOfNulls<String>(3)
//  val anyArray: Array<Any> = stringArray  -> won't compile
val anyArray: Array<out Any?> = stringArray

Primitive type arrays

Arrays of primitive types without boxing overhead: ByteArray, ShortArray, IntArray

val intArray = intArrayOf(1, 2, 3)

These classes have no inheritance relation to the Array class.

val intArray = intArrayOf(1, 2, 3)
val intArray2 = IntArray(3) // Will be initialized with 0
val intArray42 = IntArray(3) {42 } // Will be initialized with 42
val intArray4 = IntArray(3) { it * 1 } // Int array 1,2,3Code here:

Game time

Check out this code and play with it. Yay!

Resources:

Basic types | Kotlin

Oh..I just figured out that probably the best job is the one that supplies you with ugly T-shirts regularly. What do you think?