Kotlin Language Essentials for Android
var vs val, null safety, data classes, when expressions, extension functions, scope functions and fundamental Kotlin concepts
1What is the difference between 'var' and 'val' in Kotlin?
What is the difference between 'var' and 'val' in Kotlin?
Câu trả lời
'var' declares a mutable (modifiable) variable, while 'val' declares an immutable (read-only) variable. It's recommended to use 'val' by default to promote immutability and avoid bugs.
2What does the '?' operator after a type mean in Kotlin?
What does the '?' operator after a type mean in Kotlin?
Câu trả lời
The '?' operator indicates that the variable can contain null. For example, 'String?' means the variable can be a String or null. This is the basis of Kotlin's null safety system.
3What does the '!!' operator do in Kotlin?
What does the '!!' operator do in Kotlin?
Câu trả lời
The '!!' operator (not-null assertion) forces the compiler to treat a nullable value as non-null. If the value is null, a NullPointerException is thrown. Only use when you're certain the value is not null.
What is the Elvis operator '?:' used for in Kotlin?
What is a data class in Kotlin?
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