Map creation (mapOf, mutableMapOf) in Kotlin - Step-by-Step Execution

Concept Flow - Map creation (mapOf, mutableMapOf)

Start

↓

Choose map type

↓

Create read-only map

↓

Create changeable map

↓

Add key-value pairs

↓

Use map

↓

End

You start by choosing which map to create: an immutable map with mapOf or a mutable map with mutableMapOf. Then you add key-value pairs and use the map.

Execution Sample

Kotlin

val readOnlyMap = mapOf("a" to 1, "b" to 2)
val changeableMap = mutableMapOf("x" to 10)
changeableMap["y"] = 20
println(readOnlyMap)
println(changeableMap)

Creates an immutable map and a mutable map, adds a new pair to the mutable map, then prints both.

Execution Table

Step	Action	Map State	Output
1	Create readOnlyMap with pairs ("a" to 1, "b" to 2)	{"a"=1, "b"=2}
2	Create changeableMap with pair ("x" to 10)	{"x"=10}
3	Add pair ("y" to 20) to changeableMap	{"x"=10, "y"=20}
4	Print readOnlyMap	{"a"=1, "b"=2}	{a=1, b=2}
5	Print changeableMap	{"x"=10, "y"=20}	{x=10, y=20}

💡 All steps completed, maps created and printed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
readOnlyMap	empty	{"a"=1, "b"=2}	{"a"=1, "b"=2}	{"a"=1, "b"=2}	{"a"=1, "b"=2}
changeableMap	empty	empty	{"x"=10}	{"x"=10, "y"=20}	{"x"=10, "y"=20}

Key Moments - 2 Insights

Why can't we add new pairs to readOnlyMap after creation?

Because readOnlyMap is created with mapOf which makes an immutable map. The execution_table shows no step where readOnlyMap changes after creation.

How do we add a new key-value pair to changeableMap?

We use the syntax changeableMap["key"] = value as shown in step 3 of the execution_table, which updates the map.

Visual Quiz - 3 Questions

Look at the execution_table, what is the content of changeableMap after step 2?

A {"x"=10}

B {"y"=20}

C {"x"=10, "y"=20}

D {}

💡 Hint

Check the 'Map State' column at step 2 in the execution_table.

At which step does changeableMap get a new key-value pair added?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look for the step where changeableMap changes from {"x"=10} to {"x"=10, "y"=20}.

If we tried to add a new pair to readOnlyMap after step 1, what would happen?

A It would add the pair successfully.

B It would silently ignore the addition.

C It would cause a compile-time error.

D It would remove an existing pair.

💡 Hint

Recall that mapOf creates an immutable map as shown in the key_moments section.

Concept Snapshot

mapOf creates an immutable (read-only) map.
mutableMapOf creates a mutable (changeable) map.
Add pairs at creation or use [key] = value for mutable maps.
Immutable maps cannot be changed after creation.
Use mutable maps when you need to add or remove entries.

Full Transcript

This example shows how to create maps in Kotlin using mapOf and mutableMapOf. mapOf creates a read-only map that cannot be changed after creation. mutableMapOf creates a map that you can add or change entries in. We create readOnlyMap with two pairs and changeableMap with one pair. Then we add a new pair to changeableMap. Finally, we print both maps to see their contents. The execution table traces each step, showing how the maps change or stay the same. The variable tracker shows the state of each map after each step. Key moments explain why immutable maps cannot be changed and how to add pairs to mutable maps. The quiz tests understanding of these steps and concepts.