Combining flows (zip, combine) in Kotlin - Mini Project: Build & Apply

Combining Flows with zip and combine in Kotlin

📖 Scenario: You are building a simple Kotlin program that combines two streams of data (called flows) to show how they work together. Imagine you have two friends sending you messages at different times, and you want to see how their messages can be paired or combined.

🎯 Goal: Learn how to create two flows, then combine them using zip and combine functions to see the difference in how they merge data.

📋 What You'll Learn

Create two flows named flow1 and flow2 with exact values

Create a variable delayTime with the value 300L

Use zip to combine flow1 and flow2 into zippedFlow

Use combine to combine flow1 and flow2 into combinedFlow

Print the collected results of zippedFlow and combinedFlow exactly as shown

💡 Why This Matters

🌍 Real World

Combining flows is useful when you want to merge data streams, like user inputs and sensor data, to react to changes together.

💼 Career

Understanding flow combination is important for Kotlin developers working on reactive apps, especially with Android or backend services using coroutines.

1

Create two flows with exact values

Create two flows called flow1 and flow2. flow1 should emit the values 1, 2, 3. flow2 should emit the values "A", "B", "C". Use flowOf to create them.

Kotlin

# Create flow1 and flow2 with the exact values
# Your code here

Need a hint?

Use val flow1 = flowOf(1, 2, 3) and val flow2 = flowOf("A", "B", "C").

2

Add a delay time variable

Create a variable called delayTime and set it to 300L (a long number representing milliseconds).

Kotlin

import kotlinx.coroutines.flow.flowOf

val flow1 = flowOf(1, 2, 3)
val flow2 = flowOf("A", "B", "C")

# Create delayTime variable
# Your code here

Need a hint?

Write val delayTime = 300L to set the delay time.

3

Combine flows using zip and combine

Use zip to combine flow1 and flow2 into a flow called zippedFlow that emits strings like "1 - A". Then use combine to combine flow1 and flow2 into combinedFlow that emits strings like "1 + A". Use lambda parameters a and b for the values.

Kotlin

import kotlinx.coroutines.flow.flowOf

val flow1 = flowOf(1, 2, 3)
val flow2 = flowOf("A", "B", "C")

val delayTime = 300L

# Create zippedFlow using zip
# Create combinedFlow using combine
# Your code here

Need a hint?

Use val zippedFlow = flow1.zip(flow2) { a, b -> "$a - $b" } and val combinedFlow = flow1.combine(flow2) { a, b -> "$a + $b" }.

4

Print the results of zippedFlow and combinedFlow

Write code to collect and print the values from zippedFlow and then from combinedFlow. Use runBlocking and collect. Print exactly these lines before collecting: println("Zipped Flow:") and println("Combined Flow:").

Kotlin

import kotlinx.coroutines.flow.flowOf
import kotlinx.coroutines.flow.zip
import kotlinx.coroutines.flow.combine
import kotlinx.coroutines.runBlocking

val flow1 = flowOf(1, 2, 3)
val flow2 = flowOf("A", "B", "C")

val delayTime = 300L

val zippedFlow = flow1.zip(flow2) { a, b -> "$a - $b" }
val combinedFlow = flow1.combine(flow2) { a, b -> "$a + $b" }

# Collect and print zippedFlow and combinedFlow
# Your code here

Need a hint?

Use runBlocking and collect to print each flow's values. Print the labels exactly as shown.