When with multiple conditions in Kotlin - Step-by-Step Execution

Concept Flow - When with multiple conditions

Start

↓

Evaluate expression

↓

Check first condition

| Yes↓

Execute first branch

↓

End

No↓

Check second condition

| Yes↓

Execute second branch

↓

End

No↓

Check multiple conditions combined

| Yes↓

Execute combined branch

↓

End

No↓

Execute else branch

↓

End

The 'when' expression evaluates an input and checks conditions one by one, including multiple conditions combined with commas, executing the matching branch and then ending.

Execution Sample

Kotlin

val x = 3
when (x) {
  1, 2 -> println("One or Two")
  3, 4 -> println("Three or Four")
  else -> println("Other")
}

This code checks the value of x and prints a message depending on which group of values x matches.

Execution Table

Step	Expression Value	Condition Checked	Condition Result	Branch Taken	Output
1	3	1, 2	False	No
2	3	3, 4	True	Yes	Three or Four
3	3	else	Skipped	No

💡 Condition '3, 4' is True, branch executed, when expression ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	3	3	3	3

Key Moments - 2 Insights

Why does the 'when' stop checking after the first true condition?

Because 'when' executes only the first matching branch and then exits, as shown in execution_table step 2 where it stops after matching '3, 4'.

How do multiple conditions work in one branch like '1, 2 ->'?

Multiple conditions separated by commas mean 'or'. If the expression matches any of them, that branch runs, as seen in step 1 checking '1, 2'.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 2?

A "One or Two"

B "Other"

C "Three or Four"

D No output

💡 Hint

Check the 'Output' column at step 2 in the execution_table.

At which step does the 'when' expression stop checking conditions?

A Step 2

B Step 3

C Step 1

D It checks all steps

💡 Hint

Look at the 'Branch Taken' column to see when a branch is executed and the rest skipped.

If x was 5, which branch would be taken according to the execution table logic?

A "Three or Four"

B "Other"

C "One or Two"

D No branch

💡 Hint

Consider that 5 does not match any listed conditions, so 'else' branch runs.

Concept Snapshot

when (value) {
  condition1, condition2 -> action1
  condition3, condition4 -> action2
  else -> defaultAction
}
- Checks conditions in order
- Multiple conditions separated by commas mean OR
- Executes first matching branch and stops
- else handles all unmatched cases

Full Transcript

The Kotlin 'when' expression evaluates a value and compares it against multiple conditions. Each condition can have multiple values separated by commas, meaning if the value matches any of them, that branch runs. The checking stops at the first true condition. If none match, the else branch runs. For example, if x is 3, it does not match '1, 2' but matches '3, 4', so it prints 'Three or Four' and stops checking further.