Understanding the Single Exclamation Mark in Kotlin | Kotlin Programming

├Źndice
  1. What is the Single Exclamation Mark in Kotlin?
  2. How does the Single Exclamation Mark work?
  3. When should you use the Single Exclamation Mark?
  4. Conclusion

What is the Single Exclamation Mark in Kotlin?

The single exclamation mark in Kotlin is known as the "not-null assertion operator". It is a shorthand way of telling the compiler that a variable is not null and can be safely accessed. This operator is commonly used when working with nullable types in Kotlin.

How does the Single Exclamation Mark work?

When a variable is declared as nullable, it means that it can either have a value or be null. If a value is accessed from a nullable variable without first checking if it is null, it can cause a NullPointerException at runtime.

To avoid this, the not-null assertion operator can be used to tell the compiler that the variable is not null. This is done by adding an exclamation mark after the variable name.

For example, if we have a nullable variable "name", we can use the not-null assertion operator like this:


val name: String? = null
val length = name!!.length

In this example, we are using the not-null assertion operator to tell the compiler that "name" is not null, and can be safely accessed to get its "length" property. If "name" was actually null at runtime, a NullPointerException would be thrown.

When should you use the Single Exclamation Mark?

While the not-null assertion operator can be a useful shorthand, it should be used with caution. It is important to be sure that a variable is not null before using the operator, otherwise it can lead to runtime errors.

In general, it is better to use safe null checking operators like "?." and "?:" to handle nullable types in a more robust way. Only use the not-null assertion operator when you are absolutely sure that a variable is not null and you need to access its properties or methods.

Conclusion

In summary, the single exclamation mark in Kotlin is a shorthand way of telling the compiler that a variable is not null and can be safely accessed. While it can be useful in certain situations, it should be used with caution to avoid runtime errors. It is generally better to use safe null checking operators to handle nullable types in a more robust way.

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