DisplayMessageActivity Kotlin missing import and declaration

Android
1

Hello Kotlin people

I’ve been doing the developer.android tutorial (Build your first app  |  Android Basics  |  Android Developers)

In the DisplayMessageActivity file, Java version:

// Get the Intent that started this activity and extract the string
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

The corresponding snippet in the Kotlin version:

// Get the Intent that started this activity and extract the string
val message = intent.getStringExtra(EXTRA_MESSAGE)

So in Kotlin I don’t need to declare intent or to specify that EXTRA_MESSAGE comes from MainActivity?

Also in the Kotlin version I failed to import android.content.Intent in DisplayMessageActivity.kt and the app works fine?

I feel I understand what’s going on in Java but the Kotlin version confuses me a bit. Any help would be greatly appreciated!

2

As stated in the Kotlin Docs whenever Java setters and getters follow the java convention, they will be accessible in Kotlin via properties.

So if you have a java class:

public class SomeClass {
    private String name;
    public String getName() { return name; }
    public String setName(String name) { this.name = name; }
}

it will be accessible in Kotlin via a property:

val obj = SomeClass()
obj.name = "Hello"
println(obj.name)

In your case Activity has a setter and a getter for the intent, which will be accessible in Kotlin as property. As you don’t declare a local property with the intent, you don’t need to import its type.

The propper java code to the kotlin code you posted would actually be:

String message = getIntent().getStringExtra(MainActivity.EXTRA_MESSAGE);