A large part of the Android apps and the Android itself are based on Java. Java has been always known as the native Android language. But time did not stand still, so Kotlin as a modern language has came into sight and became the second official language for Android.

Kotlin is …

Open-source statically typed programming language. It is inspired by Java (fully compatible and interoperable with Java), but it has some significant improvements and additional features. In July 2011, JetBrains unveiled Project Kotlin, a new language for the JVM. The first version of Kotlin was released on February 15, 2016. In May 2019, Google announced Kotlin as the preferred language for Android development. Enterprise leaders who are making their Android apps with Kotlin: Uber, Netflix, Pinterest, Trello, Twitter, Evernote, Kickstarter, Gradle, Basecamp.

Pros of Kotlin

• Kotlin provides built-in null safety support which is much needed, especially on Android, which is full of old Java-style APIs
• Thanks to Java bytecode, you can use Java libraries and frameworks and be sure they will work with Kotlin modules.
• Code in Kotlin is much smaller than the same functionality code written in Java, which means less room for error.
• Kotlin has modern programming concepts such as delegates, extension functions, higher-order functions, and more to help developers build clean APIs;
• Kotlin incorporates coroutines, as well as interoperability with Javascript for web development.
• Kotlin app deployment is quicker to assemble and prevent applications from expanding the size
• Kotlin script helps to configure projects in Android Studio for auto-completion aids, and it helps to reduce compile-time error detection.
• Developers can benefit from a rapidly growing collection of open source projects on GitHub, many books, learning resources, and online courses;

Cons of Kotlin

• Kotlin has a steep learning curve when switching the entire team to Kotlin.
• Kotlin is slower than Java regarding compilation speed and some features of Android Studio like auto-complete.
• Kotlin developer community is still smaller than Java (for example, at Stack Overflow)
• There are few Kotlin developers available in the market for now. So, finding an experienced person is quite tricky.
• Kotlin matches weak patterns, and code readability.
• Small support community compared with Java and fewer libraries.

What Kotlin offers that Java Doesn’t

• Coroutines A coroutine is a concurrency design pattern that you can use on Android to simplify code that executes asynchronously. Coroutines help to manage long-running tasks that might otherwise block the main thread and cause your app to become unresponsive.
• Singletons A singleton is a design pattern in which a given class has only one single instance inside the entire app.
• Extension functions It allows importing a reference to a View into the activity file, allows working with that view as if a part of the activity.
• First-class delegation Effective alternative to inheritance implementation.
• Null-Safety Kotlin solves the NullPointerExceptions problem by making all types non-nullable by default.
• String Templates Developers can assign dynamic values directly to their strings and print statements in Kotlin using templates.
• Primary Constructors Are used to initialize the class. It can be declared at the class header level allowing to automatically initialize the variables.
• Lambda expressions and higher-order functions – specialized language constructs
• Type inference for variable and property types You don’t need to define the data type of a variable explicitly as the Kotlin compiler will do it for you automatically.
• Smart Casts Automatic handling of redundant casts without having to check type or having to cast inside a statement.
• Declaration site variance and type projections Kotlin doesn’t have wildcard types. Instead, it has two other things: declaration-site variance and type projections.
• Operator Overloading Kotlin allows you to provide custom implementations for the predefined set of operators on types. These operators have predefined symbolic representation (like + or *) and precedence.
• Companion Objects In Kotlin, if you want to write a function or any member of the class that can be called without having the instance of the class then you can write the same as a member of a companion object inside the class. So, by declaring the companion object, you can access the members of the class by class name only without explicitly creating the instance of the class.
• Separate interfaces for read-only and mutable collections Unlike Java, Kotlin has two different interfaces for working with collections. The plain Collection interface handles accessing data and then the MutableCollection interface handles modifying the data.
• Data Classes The concept of Data Classes represents simple classes used as data containers and does not encapsulate any additional logic. It enables us to avoid writing a lot of boilerplate code.
• Range Expressions In Kotlin we can create ranges using the rangeTo() and downTo() functions or the .. operator.

Pros of Java

• Java is easy to learn and understand.
• Works well for native as well as cross-platform apps, can work on any device, server, or operating system.
• There are many useful and tested Java libraries, open-source ecosystems available for programmers.
• This programming language is simple to use, compiling, and making debugging.
• Assembling large projects is a simple process, thanks to the accelerated assembly with Gradle.
• The build process is faster.
• Creating modular applications and reusing the parts is easier.

Cons of Java

• Java has limitations that cause problems with Android API design due to inherent limitations.
• Java is slower compared with other programming languages.
• Java requires more memory and so tends to be slower.
• Java requires writing more code, which causes a higher risk of errors and bugs.
• It is difficult to access some content that may be inappropriate for the devices you are using.

What Java offers that Kotlin Doesn’t

• Ternary operator Java has a ternary operator that works like a basic if statement that evaluates whether a condition is true or false.
• Primitive types that are not classes Char, double, float, and byte are primitive types that serve the sole purpose of containing pure, simple values of a specific type. They come with several predefined operations, they are not objects created from a class or structure in Java.
• Static members Java creates a single static member instance that is common to all instances of the class. The static keyword reflects that the particular member with which the keyword was used belongs to the type itself, not an instance.
• Wildcard types Wildcard types have several uses, including the type of a field, local variable, or parameter. Java allows developers to use this type system for advanced functionality.
• Checked exceptions In general, checked exceptions represent errors outside the control of the program. Java checked exceptions are a feature that is still in great demand of developers. Kotlin gets rid of them to keep the code more concise, but many developers still prefer it.

Summary

Many companies are adopting Kotlin as the official Android programming language. The future of Kotlin as a new Android language is certainly encouraging. Although Java will remain a popular language for a long time to come and is unlikely to be completely replaced. Both Java and Kotlin can be used to create efficient and useful applications. But Google encourages developers to start building Android apps with Kotlin and is taking an increasingly Kotlin-centric approach to modern Android development. Many Android Jetpack libraries are either written entirely in Kotlin or support Kotlin language features such as coroutines. Finally, the main “Why use Kotlin for Android” argument might be the fact that Kotlin is designed to solve Java problems. A younger and more modern programming language has pushed Java out of this area. If you need to develop a mobile app for Android, you need to look for Kotlin developers. But remember that It can be a shock to switch an entire team to Kotlin at a time, so it’s important to make this transition slowly, one person at a time.