Summary - Flow basics

Combine flow, collect and map to write an event stream.

Summary - Flow basics

In this group you learned the cold stream nature of Flow, the flow { } builder and emit, the collect terminal operator, the map/filter intermediate operators and changing context with flowOn.

Now you will combine them: build a flow and transform it with map, then chain filter and flowOf. This structure is the foundation of asynchronous data streams in Kotlin. Later, StateFlow, SharedFlow and channel-based hot streams will build on it.

Exercise flow builder and map chain

Define fun doubled(): Flow<Int> = flow { ... }.map { ... }. In the body use a for (i in 1..5) loop with emit(i); then apply .map { it * 2 }. Mark main with runBlocking; inside it call doubled().collect { println(it) }.

Show example solution

fun doubled(): Flow<Int> = flow {
    for (i in 1..5) {
        emit(i)
    }
}.map { it * 2 }

fun main() = runBlocking {
    doubled().collect { println(it) }
}

Exercise Squares with filter and map

Define fun squares(): Flow<Int> = flowOf(...).filter { ... }.map { ... }. Build the flow with flowOf(1, 2, 3, 4, 5); filter even with .filter { it % 2 == 0 }; square with .map { it * it }. Mark main with runBlocking; inside it call squares().collect { println(it) }.

Show example solution

fun squares(): Flow<Int> = flowOf(1, 2, 3, 4, 5)
    .filter { it % 2 == 0 }
    .map { it * it }

fun main() = runBlocking {
    squares().collect { println(it) }
}

Test yourself

Which of the following is a terminal operator?
- map
- filter
- flowOn
- collect
Show answer

collect — collect is terminal; it runs the flow and consumes values.
Match the Flow concepts

flow { }

Flow builder
emit

Sends a value
collect

Consumer
flowOn

Sets context

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