Async and await for concurrent results in Kotlin - Mini Project: Build & Apply

Async and await for concurrent results

📖 Scenario: You are building a simple Kotlin program that fetches two pieces of information at the same time, like ordering coffee and a sandwich together instead of waiting for one before starting the other.

🎯 Goal: Learn how to use async and await in Kotlin to run two tasks concurrently and get their results.

📋 What You'll Learn

Create two suspend functions that simulate fetching data with delays

Use async to start both tasks concurrently

Use await to get the results from both tasks

Print the combined result

💡 Why This Matters

🌍 Real World

Many apps need to do several things at once, like loading images and text together. Using async and await helps make apps faster and smoother.

💼 Career

Understanding async programming is important for Kotlin developers working on Android apps or backend services where multiple tasks run concurrently.

1

Create suspend functions to simulate data fetching

Write two suspend functions called fetchCoffee() and fetchSandwich(). Each should delay for 1000 milliseconds and then return the strings "Coffee" and "Sandwich" respectively.

Kotlin

# Write suspend functions fetchCoffee() and fetchSandwich() with delay and return strings

Need a hint?

Use suspend fun to create functions that can pause. Use delay(1000L) to wait 1 second.

2

Set up the main function with coroutine scope

Create a main function with runBlocking to start a coroutine scope. Inside it, declare two variables coffeeDeferred and sandwichDeferred that use async to call fetchCoffee() and fetchSandwich() concurrently.

Kotlin

import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.async

fun main() = runBlocking {
    // Start async tasks for coffee and sandwich
}

Need a hint?

Use runBlocking to create a coroutine scope in main. Use async to start tasks concurrently.

3

Await results from async tasks

Inside the main function, after starting the async tasks, create two variables coffee and sandwich that use await() on coffeeDeferred and sandwichDeferred to get the results.

Kotlin

import kotlinx.coroutines.delay
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.async

suspend fun fetchCoffee(): String {
    delay(1000L)
    return "Coffee"
}

suspend fun fetchSandwich(): String {
    delay(1000L)
    return "Sandwich"
}

fun main() = runBlocking {
    val coffeeDeferred = async { fetchCoffee() }
    val sandwichDeferred = async { fetchSandwich() }

    // Use await() to get coffee and sandwich
}

Need a hint?

Use await() on the deferred variables to get the actual results.

4

Print the combined result

Add a println statement inside main to print the string "Order ready: Coffee and Sandwich" using the variables coffee and sandwich with an f-string style template.

Kotlin

import kotlinx.coroutines.delay
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.async

suspend fun fetchCoffee(): String {
    delay(1000L)
    return "Coffee"
}

suspend fun fetchSandwich(): String {
    delay(1000L)
    return "Sandwich"
}

fun main() = runBlocking {
    val coffeeDeferred = async { fetchCoffee() }
    val sandwichDeferred = async { fetchSandwich() }

    val coffee = coffeeDeferred.await()
    val sandwich = sandwichDeferred.await()

    // Print the combined order
}

Need a hint?

Use println("Order ready: $coffee and $sandwich") to show the final message.