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Explain Safe call, Elvis and Not Null Assertion operator in the context of Kotlin. |
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Answer» Safe Call operator ( ?. ) - Null comparisons are trivial, but the number of nested if-else expressions can be EXHAUSTING. So, in Kotlin, there's a Safe call operator,?, that simplifies things by only doing an action when a specified reference holds a non-null value. It allows us to use a single expression to perform both a null CHECK and a method call. For example, The following expression in Kotlin name?.toLowerCase()is equivalent to the following if(name != null) name.toLowerCase()else nullElvis Operator ( ?: ) - When the original variable is null, the Elvis operator is used to return a non-null value or a default value. In other words, the elvis operator returns the left expression if it is not null, otherwise, it yields the right expression. Only if the left-hand side expression is null is the right-hand side evaluated. For example, The following expression in Kotlin val sample1 = sample2 ?: "Undefined"is equivalent to the following val sample1 = if(sample2 != null) sample2 else "Undefined"Furthermore, on the right side of the Elvis operator, we may use throw and return expressions, which is particularly handy in functions. As a result, instead of returning a default value on the right side of the Elvis operator, we can throw an exception. For example, val sample1 = sample2 ?: throw IllegalArgumentException("Invalid")Not Null Assertion Operator ( !! ) - If the value is null, the not null assertion (!!) operator changes it to a non-null type and throws an exception. Anyone who wants a NullPointerException can ask for it explicitly with this operator. For example, // KOTLINfun main(args: Array<String>) { var sample : String? = null str!!.length}The above CODE snippet gives the following OUTPUT:- Exception in THREAD "main" kotlin.KotlinNullPointerException |
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