Kotlin is a statically typed programming language that runs on the JVM. It is a concise, safe, interoperable, and tool-friendly language.
Kotlin is an object-oriented language, and thus, variables must be declared before they can be used. In Kotlin, there are two types of variables:
var
keyword.var name = "John"
name = "Jane" // Valid
val
keyword.val name = "John"
name = "Jane" // Invalid
Kotlin has a null safety feature which eliminates the risk of null pointer exceptions. To allow a variable to hold a null value, you need to declare it as nullable by using the ?
symbol.
var name: String? = null
Kotlin also has a rich set of operators that can be used on variables. These include:
+
, -
, *
, /
, %
=
, +=
, -=
, *=
, /=
, %=
==
, !=
, >
, <
, >=
, <=
&&
, ||
, !
Now that you know the basics of Kotlin variables and operators, let's move on to data types.
Kotlin has the following data types:
Char
type.Boolean
type.Array
type.String
type.In addition to the above data types, Kotlin also has a special type called Unit
. This type is used to represent a void value.
Now that you know the basics of Kotlin data types, let's move on to Kotlin operators.
Kotlin has a rich set of operators that can be used on variables. These include:
+
, -
, *
, /
, %
=
, +=
, -=
, *=
, /=
, %=
==
, !=
, >
, <
, >=
, <=
&&
, ||
, !
Now that you know the basics of Kotlin operators, let's move on to Kotlin control flow.
Kotlin has the following control flow constructs:
if
expression: Used to evaluate a boolean expression and execute a block of code if the expression is true
.if-else
expression: Used to evaluate a boolean expression and execute one of two blocks of code, depending on whether the expression is true
or false
.when
expression: Used to evaluate an expression and execute one of several blocks of code, depending on the value of the expression.for
loop: Used to execute a block of code a fixed number of times.while
loop: Used to execute a block of code multiple times, until a condition is met.do-while
loop: Used to execute a block of code multiple times, until a condition is met. The difference between a while
loop and a do-while
loop is that a do-while
loop will always execute the code block at least once.Now that you know the basics of Kotlin control flow, let's move on to Kotlin functions.
A function is a block of code that takes one or more input parameters and produces an output. In Kotlin, functions are declared using the fun
keyword.
Here is a simple function that takes two input parameters and returns the sum of those parameters:
fun sum(a: Int, b: Int): Int {
return a + b
}
If a function does not return a value, its return type should be declared as Unit
.
Here is a simple function that takes two input parameters and prints the sum of those parameters:
fun sum(a: Int, b: Int): Unit {
println(a + b)
}
Kotlin also supports higher-order functions, which are functions that take other functions as input parameters. Higher-order functions can be used to create concise and readable code.
Here is a simple higher-order function that takes a function as input and executes that function:
fun execute(f: () -> Unit) {
f()
}
The execute
function above can be used to execute any function that does not take any input parameters and does not return a value.
Now that you know the basics of Kotlin functions, let's move on to Kotlin classes and objects.
In Kotlin, a class is a template for creating objects. A class can have properties and methods.
Here is a simple Person
class with two properties: name
and age
.
class Person(val name: String, val age: Int)
To create an object from a class, you need to use the new
keyword.
val person = new Person("John", 30)
Kotlin also supports object-oriented programming. In Kotlin, an object is a singleton - there can only be one instance of an object.
Here is a simple Logger
object with a log()
method.
object Logger {
fun log(message: String) {
println(message)
}
}
To use the Logger
object, you do not need to create an instance of it. You can simply call the log()
method directly.
Logger.log("This is a log message")
Now that you know the basics of Kotlin classes and objects, you are ready to start programming in Kotlin!