Java vs. Kotlin: Which One Will Be the Best?

Java has long been the backbone of Android development, known for its strong and flexible nature, and hence is the favorite among developers all over the world. But since JetBrains came up with Kotlin in 2016 and Google declared it an official language for Android development in 2017, the debate between Kotlin vs Java for Android development is the talk of the town. As Kotlin is advanced and designed with the needs of modern development, many developers ask which is better for Android app development. 

This blog is an attempt to understand the difference between Java and Kotlin and their strengths and weaknesses, and how they fare in today’s evolving tech landscape. Whether you are a newcomer to Android development or an experienced Android developer, this guide will help you make the best choice between Java vs Kotlin for your next project.

Java and Kotlin Difference: Understanding the Basics

Java is the most well-acclaimed programming language that started its journey more than two decades ago when James Gosling developed it way back in 1995. From then on, it continued to become popular and became an active part of almost all major computer programming milestones over the years. As of now, Java holds the highest usability record with the highest number of developers and systems. Apart from this, Java has been a key contributor to the open-source community of developers as well.

In spite of this uncontested reputation of Java, Kotlin as a modern programming language fills the gap with a lot of enhancements. Especially when Kotlin was announced as the official programming language for Android development by Google at its annual Google IO 2019 event, Kotlin got a big push and several major apps finally decided to switch over to Kotlin from Java.

The Definition of Java and Kotlin

Java: Java is platform-independent ‘Write Once & Run Everywhere’ programming language which is widely known to be concurrent, class-based and object-oriented in character. The Java platform comprises an engine, a compiler and a complete set of libraries. Though Java essentially brought a paradigm-shifting approach to programming, it got a majority of the syntax from C and C++.

Kotlin: Kotlin is an open-source, JVM Based programming language that can easily be compiled into JavaScript, Android, and Native languages. Fully interpolable and compatible with Java stack of technologies Kotlin offers a great combination of both functional programming and object-oriented programming capabilities. Kotlin comes as a more concise, safe and more practically oriented language that can easily be used for all purposes where Java is used.

Origin of Java and Kotlin

Java: Java built by James Gosling and his developer team at Sun Microsystems way back in 1995 was initially intended for compiling into bytecode run on the Java Virtual Machine(JVM).

Kotlin: Kotlin was built originally by JetBrains in 2011. The company which is already known for developing several popular and widely acclaimed IDEs built something to take over the shortcomings of Java while keeping the original Java strength intact.

10 Key Java and Kotlin Differences

With a little background, you may now be wondering how the development of Kotlin will affect Java: Will Kotlin replace it? That is not so simple. There are varying opinions on the subject. So let’s start by examining their differences and later address the two arguments.

1. Null Handling

The well-known NullPointerExceptions in Java can really frustrate any one. The primary concept of NullPointerExceptions is simple; it allows the user to assign null to any variable. Without a doubt, if a user tries to use an object reference that has a null value, that’s where the import of Java Null Pointer Exception will have its jam, and the exception needs to be handled by the developer.

On the contrary, Kotlin will by default not permit any variable or object to get assigned a null value. Compile time errors will be thrown while trying to do this. Because of this, there are no NullPointerExceptions in Kotlin. However, if the developer wishes to assign null, they have to specify such a variable with the nullable flag added to it. For this, one would have to append a question mark:

val number: Int? = null

2. Extension Functions

In Kotlin, developers can increase the functionality of any class without having to inherit from the class itself, unlike the case with Java. The extension function can however be achieved by prefixing the class name to the function name by using the ‘.’ notation in Kotlin.

To add functionality to an existing class in Java, there must be a derivation of a new class from the parent classes and the functions subsequently inherited by the derived class. In other words, there is no extension function.

3. Code

One major difference between Java and Kotlin in Android development is that Kotlin is a far more considerably more code-requiring language. Indeed, it is highly concise and minimizes the chances of creating errors, ultimately making the developer’s life much less complicated.

Given that it often requires less code to assure same functionality, brevity becomes really useful when dealing with large-scale projects. Kotlin has the resources to keep it concise and straight to the point without sacrificing syntax readability.

Related: 11 Free Resources to Practice Your Java Skills and Code Like a Pro

4. Coroutines Support

By default, components of the same application are run in the same process and thread in Android, more commonly referred to as the main thread, and are responsible for the UI. Generally lengthy activities, such as network I/O and operations that consume a lot of CPU, block the calling thread until the corresponding operation has been completed. 

When you are working with Java, it is ideal to allow the creation of many background threads to assist in delaying the lengthy operations. However, managing multiple threads comes with its own challenges, a lot of them leading to further errors in codes.

Kotlin also provides the ability to create multiple threads but does it with an even simpler approach by introducing coroutines. 

How does a coroutine work then? Well, coroutines are stackless and allow the programmer to write code, suspend execution, and later continue it again. With this, non-blocking asynchronous code is written like a synchronous code. So in place of creating several threads which, later on, the programmer has to deal with, coroutines eliminate all of this overhead. They are also more concise and clear than Java solutions.

5. Data Classes

Alternatively, developers in Java have to explicitly specify the fields (or variables) in order to store the data, the constructor, and the getter and setter functions for the fields/variables along with other functions such as hashCode(), equals(), and toString().

The fact is that, these classes are mostly utility classes with a bit or no function at all.

On the other hand, in Kotlin you don’t have to bother creating data classes, all you have to do is add the word “data” to the definition of any class, and you can get the compiler to take care of the automatic generation of constructor and getter-setter operations for any number of fields/variables.

6. Smart Casting

For a developer to cast an object in Java, they need to compare the types of the variables with the execution of the operation.

In Kotlin, however, the smart casts feature does all the casting checks. There will be no redundant casts (with stable values), managed automatically by the intelligent compiler, through the “is-checks” keyword.

7. Checked Exceptions

Kotlin lacks checked exceptions. So there is no catch or throws to an exception in Kotlin. Is that good? Well, it depends. 

The evil, Java programmers, it is not just to catch exceptions but to declare them. It is highly tiresome most of the time; sometimes it is very boring. Yet, on the other hand, this makes your code much tighter and ensures that you capture the errors. The advantages and disadvantages of the support in checked exceptions have been there. It all depends on what each developer attaches the most value to.

8. Higher-Order Functions and Lambdas in Functional Programming

As said before in this article, Kotlin is an object-oriented language that also supports functional-style programming.

Functional programming is referred to as a programming style in a declarative programming language that sees computation as the evaluation of mathematical functions. High-order functions and lambda expressions are (some) concepts of functional programming.

Firstly, functions can be considered as first-class objects. Thus Kotlin would be able to take advantage of various function types to represent functions. In other words, it is possible to operate functions in multiple ways.

In addition, one can use lambda expressions or anonymous functions in Kotlin. This is called a “functional literal”. In simpler terms, it is a similar function that is specifically a non-declared function passed as an expression.

However, Java is very much affixed with the idea of object-oriented programming. But it gradually starts taking steps toward functional programming. After Java 8, they have introduced lambda expressions in 2014, which means a function without belonging to a class can be created. As a matter of fact, Java lambda can be passed as the object and invoked whenever necessary.

With the inclusion of lambda expressions, Java also extended its scope of supporting higher-order functions. In Java, functions are linked with a method, and Java 8 facilitates lambda expression’s return from methods.

Related: Learn Programming in Your Spare Time: Best 5 Languages to Consider

9. Primitive Data Types

Primitive type variables in Java are not considered objects; they are predefined data types belonging to Java itself. There are eight fundamental data types in Java – int, byte, short, double, float, boolean, char, and long. Hence, none of these variables can be in the form of an object from either a struct or a class.

Although primitive types aren’t classes, you can utilize classes wrapping a value of the primitive type. In this case, you can do this in Java by specifying it explicitly. Unlike Java, Kotlin accepts the very creation of a variable for a primitive type and automatically promotes it into an object’s domain.

10. Public Fields

The public fields (also called non-private fields) are known in Java. This proves beneficial when how an object is represented changes, as it facilitates developers to modify the object without having to modify its callers. In this way, these can become public fields while keeping the public API intact and thereby providing some maintenance aspects for the program.

Conversely, Kotlin does not have public fields.

Why Kotlin Is Better Than Java?

Kotlin has emerged as the ideal programming language choice for Android app development and this is why even Google announces it to be the official language for Android development. Here we are going to explain the reasons behind embracing Kotlin for android development.

• Enhanced Efficiency: Kotlin boasts of a very concise and highly intuitive syntax that positively boosts the efficiency of the developer team. Fewer code line and simplicity of code structure are two factors behind the increased efficiency of Kotlin.
• Completely Java-Interoperable: Kotlin is fully interoperable with Java and that’s why the Java methods can be applied with a Kotlin programming as well. This will benefit both the Java developers and the companies having large Java database.
• Easy To Maintain: Thanks to a variety of powerful IDEs, android developers can easily manage Kotlin. Apart from Android Studio and several quality SDKs, Android developers can also work with their preferred toolkit.
• Highly Reliable: One of the best things about Kotlin is that no version experiences any compatible issue. The earlier version of Kotlin is equally compatible with the latest version and vice versa.
• Lower Learning Curve: Learning Kotlin is much easier when you compare the language with Java. Most importantly, to use Kotlin in an Android development project, developers can easily take off without any prior coding exposure or experience.

Android Studio Support

Kotlin also enjoys robust support from Android Studio loaded with an extensive range of adaptation tools. Kotlin developers can work simultaneously with Kotlin and Android Studio.

The Cons of Kotlin

Despite the gamut of advantages of Kotlin over Java, Kotlin has several drawbacks as well. Fortunately, these cons never can outweigh the positive attributes of Kotlin.

• Volatile Speed of Compilation: Most Kotlin developers are of the opinion that the speed of compilation with Kotlin is very fluctuating. At times, the speed of compilation can be a lot faster and at times it can be incredibly slow.
• Lack of Community Support: Kotlin is a relatively new language and that’s why it boasts of a very limited developer community and available resources for learning the language. Kotlin developers can face a lot of queries that as of now haven’t been answered in online forums.
• Not too Many Kotlin Developers Out There: As Kotlin is a new language with just a few years of patronage and developer input, you cannot find a lot of expert Kotlin developers everywhere.

Pros and Cons of Java Language

Java as one of the oldest programming languages that has seen almost the entire horizon of the evolution of computer programming, boasts of almost equal measure of strengths and weaknesses, especially, when you compare it with Kotlin. Here we briefly explain the pros and cons of Java.

Pros of Java

• Very Simple to Learn: The idea of working with a standard programming language, such as Java, is the most mainstream and most widely used, and besides many resources for any person willing to become a developer, can be very helpful. Any developer who is just beginning will have access to a wide variety of learning resources, tools, and all kinds of community assistance.
• Highly Flexible: Java is a highly flexible language that can run on both the virtual machine and the browser.
• Android is Built with Java: Android operating system was built with Java and that is why Android boasts of several SDKs loaded with Java libraries.
• Large Ecosystem: Java boasts of a large and multifaceted open-source ecosystem of libraries and SDKs. It is also equipped for accelerated assembly in Gradle.
• More Compact: Java apps are a lot more compact compared to the apps built with Kotlin.
• Fast-paced: With a lot of established protocols, Java allows much faster pace in app development.

Cons of Java

Java over the years also shows some critical limitations for Android development. Let us have a quick look at the cons of Java.

• Limitations for Android API: Java Is said to have some limitations that cause problems with the Android API design.
• Need to Write More Code: Java developers need to write more code and this creates a higher probability of bugs and errors.
• Comparatively Slower: Java is comparatively slower in the pace of development when compared with other modern languages.