Primary constructor and init blocks in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a primary constructor in Kotlin?

A primary constructor is a concise way to declare and initialize class properties directly in the class header.

beginner

What is the purpose of an init block in Kotlin?

An init block contains initialization code that runs when an instance of the class is created, allowing extra setup beyond property declarations.

intermediate

How do primary constructor parameters relate to properties?

Parameters in the primary constructor can be used to initialize properties by prefixing them with val or var, making them class properties.

intermediate

Can a Kotlin class have multiple init blocks? What happens when it does?

Yes, a class can have multiple init blocks. They run in the order they appear in the class, each executing during object creation.

advanced

Explain the order of execution when creating an object with a primary constructor and init blocks.

First, the primary constructor parameters are passed. Then, property initializers run. After that, all init blocks execute in order. Finally, the object is fully created.

What keyword do you use to declare a property in the primary constructor?

A class

B fun

C val or var

D init

Properties in the primary constructor must be declared with val (read-only) or var (mutable).

When is the code inside an init block executed?

A When the program ends

B When the class is compiled

C When a method is called

D When an object of the class is created

Init blocks run during object creation, right after the primary constructor parameters are passed.

Can you have multiple init blocks in a Kotlin class?

A Yes, and they run in the order they appear

B No, only one init block is allowed

C Yes, but only the first one runs

D No, init blocks are not allowed

Multiple init blocks are allowed and execute sequentially in the order they are written.

What happens if you declare a primary constructor parameter without val or var?

A It is just a parameter and not a property

B It becomes a global variable

C It causes a compile error

D It becomes a property automatically

Parameters without val or var are just constructor parameters and do not become properties.

Which of these is the correct order during object creation?

A Property initializers → primary constructor → init blocks

B Primary constructor → property initializers → init blocks

C Init blocks → primary constructor → property initializers

D Primary constructor → init blocks → property initializers

First, primary constructor parameters are passed, then property initializers run, followed by init blocks.

Describe how you use a primary constructor and init blocks together to initialize a Kotlin class.

Think about how constructor parameters and init blocks complement each other.

Explain why you might use multiple init blocks in a Kotlin class.

Consider how splitting initialization into parts can help keep code clear.