Secondary constructors in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a secondary constructor in Kotlin?

A secondary constructor is an additional constructor in a Kotlin class that allows creating objects with different sets of parameters besides the primary constructor.

beginner

How do you declare a secondary constructor in Kotlin?

Use the keyword <code>constructor</code> inside the class body, followed by parameters and an optional call to the primary constructor using <code>this()</code>.

intermediate

Why would you use a secondary constructor instead of just a primary constructor with default parameters?

Secondary constructors let you provide different ways to create an object when default parameters are not enough or when you want to run different initialization code.

intermediate

What must a secondary constructor do if the class has a primary constructor?

It must delegate to the primary constructor either directly or indirectly by calling this() with appropriate arguments.

beginner

Example: What does this Kotlin code do?<br><pre>class Person(val name: String) {
  constructor(name: String, age: Int) : this(name) {
    println("Age is $age")
  }
}</pre>

It defines a class Person with a primary constructor taking name. The secondary constructor takes name and age, calls the primary constructor with name, and prints the age.

In Kotlin, how do you declare a secondary constructor?

A Using the keyword <code>init</code>

B Using the keyword <code>constructor</code> inside the class body

C Using the keyword <code>fun</code>

D Using the keyword <code>override</code>

Secondary constructors are declared with the constructor keyword inside the class body.

What must a secondary constructor do if the class has a primary constructor?

A Override the primary constructor

B Call the superclass constructor using <code>super()</code>

C Do nothing special

D Call the primary constructor using <code>this()</code>

A secondary constructor must delegate to the primary constructor using this().

Which of these is a reason to use a secondary constructor?

A To provide an alternative way to create an object with different parameters

B To replace the primary constructor completely

C To define a function inside the class

D To override a method

Secondary constructors provide alternative ways to create objects with different parameters.

Can a Kotlin class have multiple secondary constructors?

A Yes, multiple secondary constructors are allowed

B No, only one secondary constructor is allowed

C Only if there is no primary constructor

D Only if the class is abstract

Kotlin allows multiple secondary constructors in a class.

What happens if a secondary constructor does not delegate to the primary constructor in a class that has one?

A The primary constructor is called automatically

B The program runs but with warnings

C Compilation error occurs

D The secondary constructor is ignored

Kotlin requires secondary constructors to delegate to the primary constructor; otherwise, it causes a compilation error.

Explain what a secondary constructor is in Kotlin and when you might use it.

Think about creating objects with different parameters or initialization.

Describe the rules for delegation between secondary and primary constructors in Kotlin.

Focus on how constructors connect inside the class.