Preconditions (require, check, error) in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the require function do in Kotlin?

require checks a condition and throws an IllegalArgumentException if the condition is false. It is used to check arguments passed to a function.

beginner

How is check different from require in Kotlin?

check verifies a condition and throws an IllegalStateException if false. It is used to check the state of an object, not arguments.

beginner

What exception does error throw in Kotlin?

error throws an IllegalStateException with a given message. It is used to signal an unrecoverable error.

beginner

Example: What happens if require(x > 0) fails?

If x > 0 is false, require throws IllegalArgumentException with a message explaining the failed requirement.

intermediate

When should you use require vs check?

Use require to validate function arguments. Use check to verify the internal state of an object or system.

What exception does require throw if its condition is false?

A IllegalArgumentException

B IllegalStateException

C NullPointerException

D IndexOutOfBoundsException

require throws IllegalArgumentException when the condition is false.

Which function is best to check if an object's state is valid?

A check

B require

C error

D assert

check is used to verify the state of an object and throws IllegalStateException if false.

What does the error function do in Kotlin?

A Ignores the error

B Returns a boolean

C Logs an error and continues

D Throws an exception with a message

error throws an IllegalStateException with the provided message.

If you want to check a function argument, which precondition function should you use?

A check

B error

C require

D throw

require is designed to check function arguments.

What exception does check throw when its condition fails?

A IllegalArgumentException

B IllegalStateException

C RuntimeException

D IOException

check throws IllegalStateException if the condition is false.

Explain the difference between require and check in Kotlin.

Think about what each function is validating and the exceptions they throw.

Describe a situation where you would use the error function in Kotlin.

Consider when your program cannot continue safely.