In Kotlin, the condition selection can be done by using if
and when
statements.
If Statement
This is the basic syntax of if statement. The condition
must returns boolean result.
if (condition) {
// code..
}
In this example, the if statement is used to check if the value is an even number.
fun main() {
// create number variable
val number = 12
// check if number is an even number
if (number % 2 == 0) {
// if true, execute this code
println("even number")
}
}
Output
even number
Based on the code above, the number
variable is compared using ==
operator to check if the result of number % 2
is equals 0
. If the result is true, then the code inside if
block is executed.
This is the list of comparation operator that can be used in Kotlin.
Operator | Description |
---|---|
== |
Equals to |
!= |
Not equals to |
> |
Greater than |
>= |
Greater than or equals |
< |
Less than |
<= |
Less than or equals |
The other operators like AND (&&
) and OR (||
) is available.
The AND operator is an operator that returns true if the two conditions returns true.
Condition | Condition | Result |
---|---|---|
False | False | False |
False | True | False |
True | False | False |
True | True | True |
The OR operator is an operator that returns true if the one or two conditions returns true.
Condition | Condition | Result |
---|---|---|
False | False | False |
False | True | True |
True | False | True |
True | True | True |
If else Statement
The if
statement can be added with else
statement to execute certain code if the condition inside if
is not match. This is the basic syntax of using if else
statement.
if(condition) {
// code..
} else {
// code..
}
This is the example of using if else
statement.
fun main() {
// create name variable
val name = "firstname"
// check if name's value is empty
if (name.isEmpty()) {
println("name is empty!")
} else {
println("Hello, $name !")
}
}
Output
Hello, firstname !
Based on the code above, the if else
statement is used to check if the value from name
variable is empty by using name.isEmpty()
. Because the value of name
variable is not empty, the code inside else
block is executed.
Another way to create condition selection is using if else if
statement. This statement is suitable to select many conditions.
In this example, the variable called score
is checked to get the score's predicate.
fun main() {
// create score variable
val score = 78
// check the score's value to get the score's predicate
if (score >= 90) {
println("Excellent")
} else if (score < 90 && score >= 75) {
println("Very Good")
} else if(score < 75 && score >= 55) {
println("Good")
} else if(score < 55) {
println("Bad")
} else {
println("Very Bad")
}
}
Output
Very Good
Based on the code above, the if else if
is used to check the value from score
variable to get the score's predicate.
In Kotlin, to specify a range condition can be done by using in
keyword followed with range specification.
// range from 1 until 10
score in 1..10
In this example, the range condition is used to get the score's predicate from score
variable.
fun main() {
// create score variable
val score = 78
// check the score's value to get the score's predicate
if (score >= 90) {
println("Excellent")
} else if (score in 75..89) {
println("Very Good")
} else if(score in 55..74) {
println("Good")
} else if(score < 55) {
println("Bad")
} else {
println("Very Bad")
}
}
Output
Very Good
The nested condition selection is also available. This is the example of using nested condition selection using if
.
fun main() {
val email = "test@test.com"
val password = "secret"
if(email.equals("test@test.com")) {
println("Email is valid")
if (password.equals("secret")) {
println("Password is valid")
}
} else {
println("Email or password is invalid!")
}
}
Output
Email is valid
Password is valid
Based on the code above, the outer if
is executed first then the inner if
is executed.
When Statement
Condition selection with when
statement is similiar with switch case
condition selection. This is the basic syntax of using when
statement.
when(variable_to_be_checked) {
condition -> // single code..
condition -> {
// multiple line of codes with curly braces.
}
..
else -> // code for "default" condition..
}
In this example, the when
statement is used to get the job's description from job
variable.
fun main() {
val job = "Front End Developer"
when(job) {
"Front End Developer" -> println("Develop Front End App")
"Back End Developer" -> {
println("Develop Back End App")
println("Having Fun with server")
}
"Mobile Developer" -> println("Develop Mobile App")
else -> println("Just Do It")
}
}
Output
Develop Front End App
Based on the code above, the when
statement is using job
variable to check the variable's value that suitable with the specified condition. Because the value of job
variable is equals to Front End Developer
, the code is executed.
Notes
- The
if
statement is suitable for complex condition, for example a range condition. - The
when
statement is suitable for simple condition with multiple cases.
Sources
- Learn more about condition selection in this link.
I hope this article is helpful for learning the Kotlin programming language. If you have any thoughts or comments you can write in the discussion section below.
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