Get Started with Kotlin How to Create Your First Android App

Here is a step-by-step guide to building and running your very first “Hello World” app.

Building Your First App

Before you begin, ensure you have downloaded and installed Android Studio, the official Integrated Development Environment (IDE) built by Google specifically for Android.

1. Create a New Project: Select the Compose template. Open Android Studio and click Start a new Android Studio project (or File > New > New Project).

In the template selection window, choose Empty Activity.

Note: In modern versions of Android Studio, “Empty Activity” creates a Jetpack Compose project. If you see “Empty Views Activity”, that creates the older XML-based project—avoid that for this guide.

2. Configure Your App: Fill out the basic details for your app:

• Name: My First App
• Package name: com.example.myfirstapp (this acts as a unique identifier for your app)
• Language: Kotlin (this is enforced for Compose)
• Minimum SDK: Choose API 24 or higher.

Click Finish and allow Android Studio a few moments to download necessary dependencies and build the initial project.

3. Explore MainActivity.kt: Where the magic happens. Once the project loads, open the MainActivity.kt file. This is the entry point of your app. You will see code that looks something like this:

package com.example.myfirstapp

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            Greeting("Android Developer")
        }
    }
}

@Composable
fun Greeting(name: String) {
    Text(text = "Hello, $name!")
}

4. Run the App: Test your code on a virtual device. In the top toolbar of Android Studio, look for the Device Manager dropdown. Select an existing emulator (like a Pixel device) or create a new Virtual Device.

Click the green Play (Run) button. Android Studio will compile your code, start the emulator, and launch your app. You should see a white screen displaying “Hello, Android Developer!”.

Key Concepts to Understand

As you begin your journey, there are two primary concepts you’ll interact with constantly:

1. Composable Functions

In Jetpack Compose, UI components are called “Composables”. You create them by adding the @Composable annotation above a Kotlin function. Composables describe what the UI should look like based on the data passed to them, rather than dictating how to construct it step-by-step. In the code above, Greeting() is a Composable function.

2. State and Recomposition

Unlike the older XML system where you had to manually find a text box on the screen and update it when data changed, Compose is reactive. If you create a variable that holds a state (like a counter or a user’s name) and pass it to a Composable, the UI will automatically redraw itself (a process called “recomposition”) whenever that state changes.