Basics

import org.junit.Test class FakeTest { @Test fun `Just run it`() {} } // Your code starts here //sampleStart // Comments are... /* * ...the same as in Java */ fun main(args: Array<String>) { // This is a fully executable Hello World program print("Hello, World") // Hello, World } // Note that we can place functions and properties on the top level val num = 10 // Type Int is inferred from the number on the right side fun sum(a: Int, b: Int): Int { return a + b } // When a function has only one expression, we can use the shorter notation fun sum2(a: Int, b: Int) = a + b // Inferred return type is Int // it can be used as an expression, similar to a ternary operator fun bigger(a: Int, b: Int) = if(a > b) a else b class A { fun a() { print(num) // 10 print(sum(1,2)) // 2 } } fun mutability() { val a = 10 // val is read-only (final) // a = 20 // Cannot change val var b = 10 // var is mutable b = 20 // We can change var } fun nullability() { var a: String = "Str" // a = null // Error: String is not a nullable type. Use String? // Same with all other types. A is not nullable, A? is nullable var b: String? = "Str" b = null print(a.length) // print(b.length) // Error: We cannot directly use nullable types print(b?.length) // null b = "AAA" print(b?.length) // 3 } class Person( var name: String, val surname: String ) { // Method fun getFullName() = "$name $surname" // String builder override fun toString(): String = "Person(name=$name, surname=$surname)" } fun personOperations() { val user = Person("Marcin", "Moskała") // No need for `new` operator print(user.name) // Marcin print(user.surname) // Moskała print(user.getFullName()) // Marcin Moskała user.name = "Martin" print(user.name) // Martin print(user.getFullName()) // Martin Moskała } fun loop() { for (i in 1..10) { print(i) } // 12345678910 } fun operationsOnString() { var name = "Marcin" println("The trainer is " + name + ".") // The trainer is Marcin. println("The trainer is $name.") // The trainer is Marcin. name += " Moskała" println("The trainer is $name.") // The trainer is Marcin Moskała. } fun tryWhen(i: Int) { when { // When is like a if-else-if structure false -> print("This will never happen") i == 1 -> print("Printed only if i == 1") else -> print("Printed only if other conditions were not fulfilled") } } fun seeResultsOfWhen() { tryWhen(1) // Prints: Printed only if i == 1 tryWhen(2) // Prints: Printed only if other conditions were not fulfilled } fun tryWhenAsExpression(i: Int): String = when { false -> "This will never be returned" i == 1 -> "Returned only if i == 1" else -> "Returned only if other conditions were not fulfilled" } fun seeResultsOfWhenEpression() { print(tryWhenAsExpression(1)) // Prints: Returned only if i == 1 print(tryWhenAsExpression(2)) // Prints: Returned only if other conditions were not fulfilled } //sampleEnd