Lately, we wrote some of the code of SUSI Android App in Kotlin. Kotlin is a very similar language to Java but with much more advantages than Java. It is easy to adapt and learn. There is no doubt that Kotlin is better than Java but with the announcement of Kotlin Support in Google IO’17 for Android development, Kotlin seems a decent way to write code for an Android App.

Advantages of Kotlin over Java

1. 1. Reduce Boilerplate Code: It helps making development of app faster as it reduces more than 20 percent of boilerplate code. Writing long statements again and again is a headache for developers. Kotlin comes to rescue in that situation.
   2. Removes Null Pointer Exception: Once a large company faced millions of dollars of loss due to null pointer exception. It causes crashes of apps more often than anything else. Thus Kotlin helps in Null checks and makes app free from Null pointer Exceptions.
   3. Interoperable with Java: Kotlin code and Java code are interoperable. Which means you can write half your code in kotlin and half in Java and it will work like a charm. You can call java methods from Kotlin code and vice versa. So, you can simply move your existing Java based app to Kotlin slowly making your app always running.
   4. Lambda and Inline functions: Yes, Kotlin also has functionalities from functional programming languages. Mainly and most widely used feature of those languages is Lambda functions.
   5. Direct Reference of Views by Id: You do not need to write findViewById(R.id.view_name) or use any other library like Butterknife for view binding. You can simply use the view by its id.
   6. No semicolon:  Last but not the least, you do not need to add a semicolon after each statement. In fact, you do not need to add semicolon at all.

Setting up Android Studio to work with Kotlin

If you have latest Android Studio Canary Version, there is already a build support for Kotlin in it. You need not do anything in that case. But if you don’t have the Canary version, you can add Kotlin Plugin in your Android Studio. Follow the below steps to do that.

1. Install the Kotlin Plugin:

Android Studio → Preferences… →Plugins → Browse Repository → type “Kotlin” in search box → install

2. Restart your Android Studio and Rebuild the project. Everything else is already set up in SUSI Android App but if you want to do it for your other apps, follow this link.

Implementation in SUSI Android App

So, I am not going to give unnecessary code but will point out specific things where Kotlin helped a lot to reduce unnecessary code and made the code compact.

1. Listeners:

Earlier with Java

Button signup = (Button) findViewById(R.id.sign_up);

signup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
               startActivity(new Intent(LoginActivity.this, SignUpActivity.class));
            }
        });

Now, with Kotlin

fun signUp() {
   sign_up.setOnClickListener { startActivity(Intent(this@LoginActivity, SignUpActivity::class.java)) }
}

2. Models

With Java

public class MapData {

    private double latitude;
    private double longitude;
    private double zoom;

    public MapData(double latitude, double longitude, double zoom) {
        this.latitude = latitude;
        this.longitude = longitude;
        this.zoom = zoom;
    }

    public double getLatitude() {
        return latitude;
    }

    public void setLatitude(double latitude) {
        this.latitude = latitude;
    }

    public double getLongitude() {
        return longitude;
    }

    public void setLongitude(double longitude) {
        this.longitude = longitude;
    }

    public double getZoom() {
        return zoom;
    }

    public void setZoom(double zoom) {
        this.zoom = zoom;
    }
}

With Kotlin

class MapData (var latitude: Double, var longitude: Double, var zoom: Double) 

3. Constructor

With Java

public class LoginPresenter {
    private LoginActivity loginActivity;
    public LoginPresenter(loginActivity: LoginActivity){
        this.loginActivity = loginActivity;
    }
}

With Kotlin

class LoginPresenter(loginActivity: LoginActivity) {
}

Summary

So, this blog was to give you an idea about Kotlin programming language, it’s advantages over java and information how you can set it up on your Android Studio so as to help you a little in understanding the codebase of SUSI Android App a little more.

Resources

1. Official Kotlin Guide for Syntax Reference and further learning  https://kotlinlang.org/docs/reference/
2. Blog by Elye on Setting up Kotlin on Android Studio https://android.jlelse.eu/setup-kotlin-for-android-studio-1bffdf1362e8
3. Youtube Video tutorial by Derek Banas on Kotlin https://www.youtube.com/watch?v=H_oGi8uuDpA