Kotlin is a modern programming language that is designed to eliminate the null reference problem, famously termed the 'Billion Dollar Mistake' by its originator, Tony Hoare. Null safety in Kotlin is improved over Java by its robust handling of null values.
Understanding Nullability
In Kotlin, every type has an implicit nullability. Unlike Java, where all reference types can hold null, Kotlin’s type system differentiates between nullable and non-nullable data types.
To declare a variable that can hold a null value, you need to append a question mark '?' to the type:
var nullableString: String? = nullIf you try to assign a null value to a variable defined without a '?', you will get a compilation error:
var nonNullableString: String = "Hello Kotlin"// Compilation error: Null can not be a value of a non-null type String
Safe Calls
To safely access a nullable object, Kotlin provides the safe call operator ?.. When called on a variable that may be null, it will return the result or null if the variable is null.
val length: Int? = nullableString?.lengthElvis Operator
The Elvis operator ?: is used to provide a default value if the variable on the left is null.
val length: Int = nullableString?.length ?: 0This will assign 0 to length if nullableString is null.
Safe Casts
Another useful feature in Kotlin are safe casts, performed using the as? keyword, which safely attempts to cast an object to a target type. If it’s not possible to cast, it returns null instead of throwing a class cast exception.
val a: Any = "Hello"
val b: String? = a as? StringMore About Null Safety
Kotlin also supports checking for null using the !! operator. This forces a Kotlin type to be non-nullable, throwing a NullPointerException if it encounters null.
// Throws an NPE if nullableString is null
val cannotBeNull: String = nullableString!!Be judicious with its use, as it circumvents Kotlin’s rigorous null safety checks.
Benefits of Null Safety
- Reduced Null Pointer Exceptions, engraining null safety into the language design.
- Code becomes more reliable and robust.
- Easier detection and troubleshooting of nullable state issues.
Null safety in Kotlin suggests a paradigm shift from legacy programming practices, reducing runtime errors and increasing product quality. Developers find comfort in writing cleaner code that manages and protects against null values effectively.
