Flow builder and collect in Kotlin - Mini Project: Build & Apply

Flow builder and collect

📖 Scenario: You are building a simple Kotlin program that uses Flow to emit a sequence of numbers. This simulates a real-time data stream, like counting seconds or events.

🎯 Goal: Create a Flow that emits numbers from 1 to 5, then collect and print each number as it arrives.

📋 What You'll Learn

Create a Flow using flow builder that emits numbers 1 to 5

Create a val called numberFlow for the flow

Collect the flow using collect inside a runBlocking block

Print each collected number with println

💡 Why This Matters

🌍 Real World

Flows are used in Android apps and backend services to handle streams of data like user inputs, sensor data, or network responses.

💼 Career

Understanding flows and how to collect them is essential for Kotlin developers working with asynchronous data streams and reactive programming.

1

Create a Flow emitting numbers 1 to 5

Create a val called numberFlow using the flow builder. Inside the flow, emit numbers from 1 to 5 using a for loop and emit.

Kotlin

import kotlinx.coroutines.flow.flow

// Create numberFlow emitting 1 to 5
// Your code here

Need a hint?

Use flow { } to create the flow and emit(value) to send values.

2

Add runBlocking to collect the flow

Add a runBlocking block to run the coroutine. Inside it, collect the numberFlow using collect.

Kotlin

import kotlinx.coroutines.runBlocking

import kotlinx.coroutines.flow.collect

runBlocking {
    // Collect numberFlow here
    // Your code here
}

Need a hint?

Use runBlocking { numberFlow.collect { value -> } } to collect values.

3

Print each collected number

Inside the collect lambda, print each collected value using println.

Kotlin

import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.flow.collect

val numberFlow = flow {
    for (i in 1..5) {
        emit(i)
    }
}

runBlocking {
    numberFlow.collect { value ->
        // Print value here
        // Your code here
    }
}

Need a hint?

Use println(value) inside the collect block to show each number.

4

Run the program and see the output

Run the program to see the numbers 1 to 5 printed each on a new line.

Kotlin

import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.flow.collect

val numberFlow = flow {
    for (i in 1..5) {
        emit(i)
    }
}

runBlocking {
    numberFlow.collect { value ->
        println(value)
    }
}

// Run the program to see output

Need a hint?

Make sure you run the whole program to see the printed numbers.