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Android Kotlin samples
Because converting code is too mainstream.

Get started with the new official language for Android app development - Kotlin.

• Getting Started
• FindViewById
• OnClickListeners
• Start a new activity
• AsyncTasks

As of now Kotlin based IDE hasn't officially launched yet. But we are developers eh! Follow this link to download Android studio 3.0 (Canary) :

Android studio 3.0 preview
If you are working on a stable version then don't freak out. This version won't affect your existing work/settings/environment etc.

Till now we were using

...TextViewtextView = (TextView)findViewById(R.id.text_view);ButtonbuttonView = (Button)findViewById(R.id.button_view);...

In Kotlin we do:

...val textview= findViewById(R.id.text_view)asTextViewval buttonView= findViewById(R.id.button_view)asButton...

Method accessability remains to be same:

textview.setText("Hello World. This is Kotlin!")

Oh and did I mention you don't have to worry about semicolons? No? Well now you know.

In Java we did

button.setOnClickListener(newOnClickListener() {publicvoidonClick(Viewv) {Toast.makeText(this,"Hey there!",Toast.LENGTH_LONG).show();    }});

Here is the Kotlin code:

button.setOnClickListener(object:View.OnClickListener{overridefunonClick(v:View?) {Toast.makeText(this@MainActivity,"Hey there!",Toast.LENGTH_SHORT).show()         } });

Notice that insidesetOnClickListener method we are passing anobject of View->OnClickListener (Interface). So instead of usingnew, in Kotlin we doobject:
This is a short example but here Kotlin bags all the points when it comes to code readability.

In Java we started a new Activity through Intents like:

Intentintent =newIntent(this,SecondActivity.class);startActivity(intent);

In Kotlin we do:

val trigger=Intent(this@MainActivity,SecondActivity::class.java) startActivity(trigger)

Heretrigger is the Intent object.The second parameterSecondActivity::class.java looks fishy right? Well this is how we pass a reference to a class (in this case our activity) in Kotlin. See this link for more information:Class references in Kotlin

val intent_get_data= intentval ssbat= intent.getStringExtra("yolo")

In Kotlin we don't use methods likegetIntent(). Instead we have 'intent' which acts as a wrapper fpr these functions. Next we see that we don't have to specify the data type to store value from the received intent, just like in Python. This makes our code a hella more short,and enhances readability too.

To create an object of a class in Kotlin we used theobject keyword. Similarly here also we'll use this to make object of our AyncTask class.Notice that you can copy and paste your Java code and Studio will automatically convert it to Kotlin.Kotlin code:

object:AsyncTask<Void,Void,String>(){overridefundoInBackground(varargparams:Void?):String {var sampleJson:String="https://gist.githubusercontent.com/hanuor/c3a94602155d23e46daac9c18903899d/raw/ae5313ad810308dcfbfda2dda75bcee73c8830d6/sampleJson"//Do some task heretry {//some task hereLog.d("SecondActivity",""+ jsonObject)               }catch (e:Exception){                   e.printStackTrace()               }return sampleJson           }overridefunonPostExecute(result:String?) {super.onPostExecute(result)Toast.makeText(this@SecondActivity,"HelloWorld"+ result,Toast.LENGTH_SHORT).show()           }       }.execute()

object:AsyncTask<Void,Void,String>()

We are creating an object of AsyncTask task here. This takes three types of parameters<params, progress, result>. Next comes the overriding of thedoInBackground function. Take a look if you're finding this line of code difficult to understand:Functions in KotlinNext we haveresult: String? . So this means that we have a variable 'result' of String datatype. '?' is written here to allow 'result' to be null. See this for more reference.Null safety in Kotlin