kotlin variable possiblement null
1. Declare a nullable variable in Kotlin
In Kotlin, you can declare a variable that can hold a null value by adding a question mark ?
after the type declaration. For example:
var nullableVariable: String? = null
In this example, nullableVariable
is a variable of type String?
that can hold a string value or a null value.
2. Assign a value to the nullable variable
To assign a value to the nullable variable, you can use the assignment operator =
as you would with any other variable. For example:
nullableVariable = "Hello, World!"
In this case, the value "Hello, World!"
is assigned to the nullableVariable
.
3. Access the value of the nullable variable
To access the value of a nullable variable, you need to use the safe access operator ?.
. This operator ensures that the code only executes if the variable is not null. For example:
val length = nullableVariable?.length
In this example, nullableVariable?.length
returns the length of the string if nullableVariable
is not null, and null
otherwise.
4. Check if the nullable variable is null
To check if a nullable variable is null, you can use the null check operator != null
. This operator returns true
if the variable is not null, and false
otherwise. For example:
if (nullableVariable != null) {
// Variable is not null, perform some operation
} else {
// Variable is null, handle the null case
}
In this case, the code inside the if
block is executed if the nullableVariable
is not null, and the code inside the else
block is executed if it is null.
5. Safely access the value using the Elvis operator
The Elvis operator ?:
allows you to provide a default value in case the nullable variable is null. It is used in the following way:
val length = nullableVariable?.length ?: 0
In this example, if nullableVariable
is not null, nullableVariable?.length
is returned. Otherwise, the value 0
is returned.
6. Convert a nullable variable to a non-null variable
If you are sure that a nullable variable will never be null at a certain point in your code, you can convert it to a non-null variable using the not-null assertion operator !!
. However, if the variable is null at that point, a NullPointerException
will be thrown. For example:
val nonNullVariable = nullableVariable!!
In this case, nullableVariable!!
converts nullableVariable
to a non-null variable nonNullVariable
.
These are the steps involved in handling nullable variables in Kotlin.