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What's the difference between "!!" and "?" in Kotlin?
In this article, we will take an example and demonstrate the difference between (!!) and (?) in Kotlin.
Example – "!!" and "?" operator in Kotlin
Kotlin provides a wonderful operator to check NULL pointer exceptions. It throws a NULL pointer exception instead of breaking the programming logic whenever the variable is NULL.
In the following example, the value of "test" is NULL. Hence, Kotlin will throw a NULL pointer exception instead of breaking down the logic. The example shows the different uses of "!!" and "?" operators.
fun main(args: Array<String>) { val nullValue: String ?=null // it will print null println("The value is ->"+nullValue?.length) // it will throw the exception println(nullValue!!.length) }
Output
On execution, it will produce the following output −
The value is ->null Exception in thread "main" java.lang.NullPointerException at MainKt.main(main.kt:8)
The following table sums up the difference −
Input | <<Val>>?.length | <<Val>>!!.length |
Input is null | null | Null pointer exception |
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