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.