Kotlin vs Java: Key Differences You Need to Know

Wondering which language to choose for Android development—Kotlin or Java? Both are powerful, but they offer different strengths.

Java has been the go-to for years, and it is trusted for its reliability and extensive ecosystem. It's perfect for large, complex projects that require stability. On the flip side, Kotlin is more modern, with clean syntax that cuts down on errors and makes development faster. It’s becoming the favorite of Android developers, and Google loves it.

Choosing between Kotlin and Java depends on your project. Want something fresh and efficient? Go for Kotlin. Need time-tested reliability? Stick with Java.

In this article, we’ll highlight 12 key differences between these two languages. Let’s find out which one works best for you!

Kotlin Vs Java: Understand the Basics

In the field of Android app development, Google Play has the leading position in the mobile market. Java has been the language of answers for the building of Android applications for many years. 

But then Kotlin came along, and the dynamic changed totally. Still a strong competitor, Java has been losing ground to the point where Kotlin has become widely popular among developers. So the battle for Java or Kotlin has been ongoing for some time now. 

Some people regard Java as the "Official" choice, but many tech startups are now heading to Kotlin for its clean and tidy syntax. But which one should you choose? 

Let’s break it down and understand the basics first.

What is Kotlin?

Kotlin is a relatively recent programming language, developed by JetBrains, and released in 2011. It is aimed as a more compact, readable, and practical option to Java. One of the best parts? It’s fully compatible with Java code, so you can easily integrate it into your existing projects. 

Features of Kotlin:

• Open Source
• Extensibility
• Efficient and Clean Code
• No Runtime Overhead
• Compiled to JavaScript
• Compiles to JVM Bytecode

What is Java?

Java, which was created by James Gosling at Sun Microsystems (now Oracle) in 1995. It is a stable and versatile general-purpose-object-oriented programming language. Java will run on any device, operating system, and server, and the fact that it is compiled into byte code means it can run on any Java Virtual Machine (JVM). 

On top of that, Java static typing catches errors at compile-time, reducing bugs. And Java frameworks simplify development with pre-built classes, letting developers focus on business logic. Thus, Java is still a dominant language in many industries. When you want to tackle complex backend solutions, it's smart to hire Java developers who know the ins and outs of the language.

Features of Java:

• Dynamic
• Multithreaded
• Object-Oriented
• Neutral Architecture
• JIT Compiler
• Portable

Difference between Kotlin and Java

Kotlin and Java are both programming languages used to create apps for the Java Virtual Machine (JVM). But they have some differences, such as:

1. Null Safety

In Java, NullPointerExceptions (NPEs) are a common headache. They occur when you try to use a variable with a null value, causing your program to crash. Developers spend a lot of time handling these exceptions.

In Kotlin, null safety helps avoid this. By default, you can’t assign null to a variable unless you explicitly make it nullable by adding a ?. If you try to assign null to a non-nullable variable, the code will fail at compile time—no surprises during runtime.

For example:

val number: Int? = null

Kotlin makes managing null values safer and easier!

2. Data Classes

In Java, if developers want to create a data class, they would have to declare fields, constructors, getter and setter methods, hashCode(), equals(), and toString() functions. 

This can get stale after a while, particularly for data-centric classes. So this would be more work in Kotlin than in Kotlin itself, but with Kotlin we simply need to start the class with the data keyword. 

It generates the constructor and other necessary methods automatically, which reduces boilerplate code and speeds up the creation of data classes. In Kotlin, this method makes the code more compact, leading to cleaner, and more maintainable.

Pro Tip: For data-heavy projects, Kotlin is a lifesaver. You’ll save hours by not needing to write boilerplate code.

3. Smart Casts

When you’re casting objects, Kotlin makes it a lot easier. The smart casts feature automatically checks for types, so you don’t have to manually cast every time you want to operate on an object, unlike Java, where casting is often a manual task.

This feature makes Kotlin code more elegant and less error-prone. To take advantage of this feature, consider hiring Kotlin developers who can implement smart casts effectively and make your code cleaner and more efficient.

4. Coroutines Support

Handling background tasks in Java can be a bit of a nightmare—you end up juggling multiple threads, which gets complicated fast. Kotlin introduces coroutines, which let you write non-blocking code as if it’s synchronous. It’s like creating multiple tasks without overloading your brain with thread management!

Quick Tip: If you're building apps that handle network requests or heavy computation, coroutines can make your code cleaner and easier to maintain.

5. Checked Exceptions

have to catch or declare exceptions explicitly, which makes the code simpler and less cumbersome.

Java forces developers to catch checked exceptions which can be time-consuming. However, it makes sure that errors are handled properly, thus making the code more robust.  Whether this is a good thing depends on what you value more—simplicity or error handling.

6. Extension Functions

In Kotlin, it is possible to extend the behavior of a class without inheriting from it. It's a case of giving an established hero new powers, all without reworking the whole history. In Kotlin, you simply use the '.' notation to extend the class.

Java, on the other hand, doesn’t have extension functions. New functionality must be defined through the creation of a new class and inheriting that class from an existing class. Extensión functions in Kotlin are a time-saver, particularly when developing projects of large sizes.

7. Code

One major difference between Kotlin and Java is the amount of code required. Kotlin is much more compact than Java and it is feasible to replicate the same task with a much fewer number of characters in the code. This is a process that leads to a lower rate of error, resulting in faster and less cumbersome design.

Because of the brevity of Kotlin, it is simpler to manage projects as less code is needed to accomplish the same functionality as with Java. Despite its shortness, the readability of Kotlin is not compromised, and the syntax remains straightforward to read.

8. Functional Programming

Kotlin is a hybrid approach programming language combining object-oriented and functional programming. It lets you treat functions as first-class citizens: passing them around to be arguments; returning them as results; and so on.

Another feature of Kotlin is lambda expressions — anonymous functions that you can use inline. This is more elegant than a loop and makes your code cleaner and more concise, allowing powerful functional programming features such as higher-order functions that take other functions as arguments or return them.

As for Java, it is primarily object-oriented, but it now includes functional programming features since version 8 in the form of elements like lambda expressions. 

Java currently supports basic lambda expressions and higher-order functions but keeps its strong reliance on an Object-Oriented structure. Java's approach is more adhesive than Kotlin's, which draws functional programming in with an easier ally.

9. Primitive types

Java has primitive types like int, char, and double, which are not objects. While this is efficient in terms of memory, it can be a bit restrictive. You often have to use wrapper classes like Integer or Double to treat primitives as objects.

Kotlin takes a more relaxed approach. It automatically treats primitive types as objects, meaning you get the best of both worlds: efficiency and flexibility.

10. Public Fields

In Java, public fields are common, allowing you to modify the internal state of objects directly. It’s quick and dirty but can lead to maintenance headaches down the road.

Kotlin doesn’t have public fields. Instead, it uses properties—a more modern and controlled approach to handling object data. This leads to better encapsulation and makes your code more maintainable.

11. Wildcard Types

In code, a question mark (?) (Pascal) is often used as a wildcard, standing for an unknown type (for variables, fields, or parameters)

But unlike Java, Kotlin has no concept of wildcard types. In contrast, Kotlin relies on declaration-site variance and type projections for similar functionality, allowing for a clearer and safer approach to working with generics. That ensures type constraints during compilation.

12. Implicit conversions

Java makes life easier by supporting implicit conversions, meaning it automatically converts smaller types (like int) into larger types (like long) without needing explicit code.

Kotlin, however, is a bit stricter. It doesn’t allow implicit widening conversions, so you’ll need to manually cast smaller types into larger ones when necessary. It’s a bit more effort, but it also prevents unintended errors.

Kotlin vs Java Use Cases

Both Kotlin and Java are powerful programming languages used for specific development purposes. When deciding Java vs Kotlin for Android, it’s important to understand the strengths and ideal use cases of each language. Kotlin and Java are powerful languages used in different areas of software development. 

Here is a list that shows the use cases for both languages and can help developers make a fair decision based on the requirements of the project.

Kotlin Use Cases

Java Use Cases

Companies Using Java vs Kotlin

Both Kotlin and Java are the most adopted programming languages, and each has its strengths to suit different industries. Java is quite an old language that is preferred by a huge number of notable organizations, alongside the certainty of being a dependable and notoriety language. Kotlin is newer than Java and has gained popularity, particularly for mobile apps, and is also used by many enterprises for web apps. When companies decide to go with either Kotlin or Java, that decision generally comes down to their project needs, their existing tech stacks, and the experience of their developers. Here are a few popular companies that use both languages:

Companies Using Java

Companies Using Kotlin

Kotlin vs Java: Which is Better?

In the ongoing debate of Kotlin vs Java, isn’t easy to settle. The answer depends on what you're working on. Both have their unique strengths! 

Kotlin is quickly becoming the go-to language for Android development. With cool features like extension functions, coroutines, and a focus on null safety, it makes life so much easier for developers. Plus, its growing community and constant updates make it a great choice if you’re looking to hire Kotlin developers for your mobile app.

That said, Java isn’t going anywhere. It continues to be a powerhouse in terms of a rich ecosystem and a long history of reliability (decades in some cases). Although Kotlin is becoming more popular, Java continues to be the software of choice for backend systems, enterprise applications, and others. 

So, is Kotlin replacing Java? Not exactly. While it is not so difficult to say that Kotlin is there to say that in many places Java is still the king technology. There is theirs and still Java is a good platform to work with in the technical field. It’s all about what works best for your project!

Wrapping it up!

And that wraps up our Kotlin vs Java comparison! In this blog, we've covered the key points to help you decide which language is the best fit for your next project. Both languages have left a huge mark on the development world. While Kotlin is making waves, especially for Android development, Java is still holding strong and has a bright future ahead.

Quick note: If you’re diving into Android app development or server-side programming, Kotlin is a solid choice. But, if you’re working on enterprise apps, desktop software, or web applications, Java continues to be the go-to language.

Ultimately, the right language depends on your project, but now you’ve got the info to make the best choice!