Get Started with #Kotlin on #Android

Kotlin is fully supported in Android Studio 3.0 and higher, so it's easy to create new projects with Kotlin files, add Kotlin files to your existing project, and convert Java language code to Kotlin. You can then use all of Android Studio's existing tools with your Kotlin code, such as autocomplete, lint checking, refactoring, debugging, and more.

https://kotlinlang.org/docs/tutorials/kotlin-android.html

Create a new project with Kotlin

Using Kotlin with a new project requires just one extra click in the New Project wizard:

1. In Android Studio, click File > New > New Project. Or if you've just opened Android Studio and see the Welcome to Android Studio window, click Start a new Android Studio project.
2. On the first screen, check Include Kotlin support. That's the only difference.
3. Click Next and continue through the wizard until you're done.

#Modern. #Expressive. #Safe.

Safer Code

Write safer code and avoid NullPointerExceptions in your app.

//Kotlin

var output: String
output = null   // Compilation error

==================================

val name: String? = null    // Nullable type
println(name.length())      // Compilation error
          

Readable and Concise

Data Classes

Focus on expressing your ideas and write less boilerplate code.

//Kotlin

// Create a POJO with getters, setters, equals(), hashCode(), toString(),
// and copy() with a single line:

data class User(val name: String, val email: String)
          

Lambdas

Use lambdas to simplify your code.

//Java

button.setOnClickListener(new View.OnClickListener(){
    @Override
    public void onClick(View v){
        doSomething();
    }
});
          
//Kotlin

button.setOnClickListener { doSomething() }
          

Say Goodbye to findViewById

Avoid findViewById() calls in your code. Focus on writing your logic with less verbosity.

//Kotlin

import kotlinx.android.synthetic.main.content_main.*

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // No need to call findViewById(R.id.textView) as TextView
        textView.text = "Kotlin for Android rocks!"

    }
}
     

Extend functionality without inheritance

Extension functions and properties let you easily extend the functionality of classes without inheriting from them. The calling code is readable and natural.

//Kotlin

// Extend ViewGroup class with inflate function
fun ViewGroup.inflate(layoutRes: Int): View {
    return LayoutInflater.from(context).inflate(layoutRes, this, false)
}

==================================

// Call inflate directly on the ViewGroup instance
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
    val v = parent.inflate(R.layout.view_item)
    return ViewHolder(v)
}

100% Interoperable with Java

Add as little or as much of Kotlin as you want. Kotlin is a JVM language that's completely interoperable with Java.

//Kotlin

// Calling Java code from Kotlin
class KotlinClass {
    fun kotlinDoSomething() {
        val javaClass = JavaClass()
        javaClass.javaDoSomething()
        println(JavaClass().prop)
    }
}

==================================

// Calling Kotlin code from Java
public class JavaClass {
    public String getProp() { return "Hello"; }
    public void javaDoSomething() {
        new KotlinClass().kotlinDoSomething();
    }
}