Kotlin vs. Java: Key Differences

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What is Kotlin?

Kotlin is a statically-typed, open source programming language. It is designed to be interoperable with Java and provide a cleaner, simpler, and a faster mixture of object-oriented, and functional programming. Kotlin is the brainchild of JetBrains and in 2011 they unveiled Project Kotlin, which served as a new language for the Java Virtual Machine. JetBrains set out to create a new language, with all of the features they needed, and the compile speed of Java. In 2012, JetBrains open-sourced the Kotlin project, under the Apache 2 license. It wasn’t until February 15, 2016, that Kotlin 1.0 was released.

This guide provides an introduction to Kotlin, including its key features, differences with Java, and how it can be used to create a server-side applications.

Key Features of Kotlin

Kotlin includes several features that make it a good choice for developers. Those features include:

  • Interoperability with Java.
  • Clean, compact syntax.
  • Offers both functions and functional programming.
  • Includes data classes.
  • Reduces code length (approximately 20% less code when compared to Java).
  • Statically typed.
  • Extendable, via functions.
  • Fewer runtime crashes.
  • Smart cast function that help improve an application’s performance.
  • Open-source, so it has a low cost of adoption.
  • Does not have checked exceptions.
  • Supports multiple threads to run intensive operations.
  • Supports coroutines.

What is Kotlin Used For?

Because Kotlin compiles to Java bytecode and the runtime is a single JAR, you can use Kotlin anywhere you would use Java. Kotlin code can be compiled to JavaScript, so you can use it to write frontend web application code. Kotlin’s is very popular for Android development and provides a way to share code between mobile platforms.

Other uses for Kotlin include:

  • Backend and server-side development.
  • Data science (as a replacement for Scala/Python).
  • iOS applications.
  • Embedded systems.
  • Data analysis.
  • Game development.

Kotlin and Java: How are they Different?

There are several key differences between Kotlin and Java. The biggest difference between the two languages is that Kotlin doesn’t provide for checked exceptions. This means there’s no need to catch or declare any exceptions. The lack of support for checked exceptions can be considered a pro or a con depending on your preference as a developer. If you dislike having to use try and catch blocks in your Java code, then Kotlin’s omission of checked exceptions is a welcome change. However, if you see checked exceptions as a solid means for error recovery, you might find Kotlin a bit frustrating.

Another big difference between Kotlin and Java is the brevity of Kotlin code. A perfect example of this is a basic “Hello, World!” program. In Java, the code for this resembles the following:

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class MyClass{
  public static void main(String args[])
  {
      System.out.println("Hello World");
  }
}

In Kotlin, this same code is written as follows:

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fun main(args:Array){
  println("Hello World");
}

That’s half the amount of code lines in Kotlin. If you’re working with a larger application, programming with Kotlin reduces the amount of code you have to write.

In Java’s favor, it enjoys a much larger community, since it’s been around much longer –since 1995. This means there are considerably more resources available for Java in comparison to Kotlin.

Other differences between Kotlin and Java include:

  • Kotlin supports smart cast (a function that identifies immutable types and performs implicit cast by the compiler). For example, class casting in Java requires first checking the type of variable using the instance of operator and then casting it to the target type. With Kotlin, when performing !is or is checks on a variable, the compiler tracks the information and automatically casts the variable to the target type.

  • Kotlin supports type inference, whereas, with Java, types must be specified explicitly.

  • Java compilation time is 15-20% faster than Kotlin compilation time.

  • With Kotlin, it’s not possible to assign null values to variables or return values. With Java, null values can be assigned, but accessing objects pointing to null values raises an exception.

  • Kotlin supports extension functions, whereas Java does not.

  • Kotlin uses invariant arrays which means the language doesn’t allow a user to assign Array<string> to Array<any>. This feature prevents runtime failures, which is an issue found in Java.

Kotlin for Server-Side Applications

Kotlin can be used to develop server-side application code. When using Kotlin for this purpose you gain several benefits which include:

  • Features such as type-safe builders and delegated properties make it possible to build powerful abstractions.
  • Coroutine support makes it possible to scale server-side applications.
  • Java interoperability means you can continue using Java while gaining the modern benefits of Kotlin. Since Java has one of the largest programming ecosystems in the world, this is a big plus.
  • Supports gradual migration from Java.
  • Supports framework-specific tooling.
  • Null-safety helps eliminate issues with dereferencing null values.
  • Intuitive action chains make it possible to easily transform a list of X objects to Y objects (for example listOf(X(1), x(2), and X(3)).map { x -> x.toY() }).

For those who depend on frameworks, Kotlin enjoys the support of several.

Spark Framework, not to be confused with Apache Spark, was originally a web framework for Java development, and it now supports Kotlin. Spark makes it possible to build expressive web applications using declarative syntax.

Ktor was developed by JetBrains and is used to build connected applications. Ktor offers strongly-typed endpoints and makes it possible to exchange data across platforms. Ktor assists you with building asynchronous client and server-side applications, ranging from microservices to multiplatform HTTP client applications.

Javalin isn’t a full-blown framework, but rather a REST API library that supports template engines, WebSockets, and static file-serving. Javalin also includes a built-in Jetty server and template/markdown rendering.

Spring introduced support for Kotlin in version 5.0 and is one of the more popular tools for building enterprise-level web applications. Spring is a module MVC framework, which means you only have to use what you need. Spring is a great framework for building web applications, enterprise applications, REST APIs, and distributed systems.

Conclusion

For anyone looking to the future of Android app development, Kotlin is the way to go. With a concise language, efficiently compiled code, extendability, and plenty of other attractive features, Android developers can do much more with far less. If you’re more of a general-purpose Java developer, you can still benefit from Kotlin, thanks to seamless interoperability. Those who already know Java can get up to speed with Kotlin in no time. Check out Kotlin to see if it doesn’t become your go-to language for Android and server-side application development.

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