Kotlin vs. Java For Android Development Ultimate Comparison

Using Java vs. Kotlin for Android OS is one of the main dilemmas of mobile developers. Both variants are popular globally and are among the actively used languages. According to Statista, Java ranks 6th on this list with 33.27%, while Kotlin ranks 15th with 9.16%. Each has its own characteristics and is suitable for projects of different levels of complexity. In this article, we will compare these options in terms of effectiveness for creating Android apps.

Kotlin or Java for Android, which is better for Android development in 2023?

Java has a highly competitive position in the overall list of programming languages. It is second only to such "giants" of software development as JS, HTML/CSS, SQL, Python, and TypeScript. In other rankings, it also stands out brightly. Thus, the global Java community is at the 3d position (14 million), and higher are only Python and JS (15.7 and 17.4 million, respectively). What about Kotlin?

This language was first introduced in 2011; version 1.0 stable release appeared in February 2016, and 1.1 in March. Thus, Kotlin is 16 years younger than Java, which determines the difference in the breadth of documentation, availability of libraries, and ready modules. It is noteworthy that it was created as a replacement for Java in Android OS and is a serious competitor in this area.

The debate around Kotlin vs. Java for Android flared up with renewed vigor in May 2019. At that time, Google named the language as the preferred choice for Android, explaining it as an opportunity to write less code. Kotlin has a fairly large global community (5 million) and is valued by mobile developers for its more innovative (simple and flexible) approach to development.

Choosing between Java vs. Kotlin for Android app development can be difficult because each option has advantages. For example, the "young" Kotlin is clearly ahead of Java in terms of code writing speed. At the same time, achieving results with the first is problematic without knowledge of the second because Kotlin is based on the JVM and, at the moment, is not a complete alternative.

Let's take a closer look at both languages to understand better their capabilities from both a developer and business perspective.

What Is Java?

Short review

It is a multi-platform object-oriented programming language created by Sun Microsystems (later to become a subsidiary of Oracle). It is also a computing platform for building apps. With the help of a set of programs, specialists efficiently implement and run projects. Development is possible in the IDE Android Studio, NetBeans, and Eclipse.

The language and API represent the external interface between the developer and the Java platform. The internal communication between the platform and the hardware is the responsibility of the Java virtual machine (JVM), which is an additional layer of abstraction. The source code runs on the machines on which the JVM is installed.

It is a solid foundation not only for Android applications but also for large-scale enterprise software, scientific solutions, big data analytics, and server technologies (Apache, GlassFish, JBoss, etc.). 

Benefits for Developers

To begin with, it is one of the easiest languages to learn and use. Its syntaxes are easy to understand, especially for those with a good knowledge of C++. The lack of complex and rarely used features, such as operator overloading, and the presence of Automatic Garbage Collection also increase usability. 

There are many more reasons why Android developers choose Java:

• OOPS Concept. A program is viewed as a set of objects interacting with each other. Each of them has its own properties and behavior. This approach speeds up code writing, makes it more readable and understandable, and simplifies scaling. 

• Open Source. Developers get free access to a variety of libraries, which makes the workflow faster and the team's productivity higher. In addition, the speed of work is positively affected by the fact that the language is high-level and, therefore, more understandable to write and read.

• Wide range of tools. The team can tailor powerful tools to the needs of the project. This advantage applies not only to coding but also to error detection, localization, and troubleshooting.

• Independence from the platform. "Write Once Run Anywhere" describes the cross-platform capabilities of the language. The developed program can be compiled into standard bytecode and run on any device with the JVM. This is done using the optional Android SDK tool from Google. 

• Security. All components (compiler, interpreter, and runtime environment) are based on Java to meet security requirements. The built-in security features include a sandbox environment, cryptography for authentication, etc.

Writing code, compiling, and debugging are easier and more efficient than with many other languages. This plays an important role in the success of a project. 

Benefits for Businesses

Based on the unique features of Java, you can:

• integrate high-performance features into the application and tailor them to target users;

• expand creativity through an extensive ecosystem of libraries, frameworks, and tools;

• ensure security through enhanced protection against malware, hacking and other threats;

• offer the target audience a high-end experience using the app based on Java, particularly easy upgrades to new versions.

Using Java technology, proven by millions of developers, allows you to bring your product to market without delay and provide a high return on investment. 

What's new in 2022

As of September 2022, the last released version is Java 19. A few main innovations:

• preliminary support for record patterns;

• preliminary implementation of the Vector API with functions for vector calculations;

• preliminary support for the FFM API;

• experimental API for structured parallelism;

• support of virtual threads for easy writing of high-performance applications.

The version with long-term support (LTS) is Java 17. It was released in September 2021. As early as March 2023, Java 20 is promised. Since new versions are scheduled every 6 months, Java 21 (with LTS) should be expected in September 2023. 

With Kotlin, things are no less interesting. Let's look at its key features below.

What is Kotlin?

Short review

It is a statically typed language (the type of a variable is known at compile time before the program even runs) that supports the object-oriented approach (OOP). JetBrains authors aimed to create a language that would be more concise than Java and simpler than Scala. As of 2017, it is the official language for Android. 

The language runs on top of the JVM and is fully compatible with Java. It embeds Android, so developers can embed new functions into an existing app. It can potentially be used wherever Java is available, including web development, desktop, backend, and other tasks. IntelliJ IDEA or Android Studio is typically used as an integrated development environment.

For these and other advantages, it is valued by mobile developers, and companies choose it for their projects. 

Benefits for Developers

The language is easy to learn for experts familiar with Java, but there are few tutorials for beginners. The creators have tried to consider all the shortcomings inherent in Java and other languages to make the syntax concise and easy to use. This means that the code is very easy to read and, sometimes, can be dozens of lines shorter than its competitor. 

Strong features of Kotlin that are important for development:

• Interoperability with Java. Functions declared in Java code can be called directly from Kotlin code and vice versa. In addition, the team can use many Java-based libraries and frameworks. This compensates for the lack of libraries in this young language. 

• Laconic constructions. The authors originally focused on compactness. Not surprisingly, the language allows you to describe in one line what you would need eighteen lines to do in Java. This is one of the main factors in choosing Kotlin.

• Availability. The code is open to programmers and is provided free of charge. The language developers consider the opinions of concerned third-party specialists and make changes suggested by the global community.

• Additional features. The language has useful functions that are not in Java. For example, data class and null protection. This increases usability for developers working on complex projects.

• Reliability and stability. The same company creates the language and programming environment, which constantly maintains security. The compiler's commitment to fault tolerance makes it easier to find bugs in the code and fix them.

Kotlin offers a more modern approach where the problem can be solved with several times less code. This has a positive effect on the quality of the implementation of the IT idea.

Benefits for Businesses

With Kotlin, you have the ability to:

• speed up work on the product by writing shorter and more readable code;

• reduce the likelihood of errors and bugs in the app and ensure fault tolerance;

• avoid Java flaws, such as preventing the "billion dollar bug" associated with null references;

• introduce new functionality into an existing Java app without having to rewrite it.

If you choose this language, you get the features that Java provides, such as access to a huge number of libraries. At the same time, you will avoid its many disadvantages. 

What's new in 2022

In April 2022, there was an incremental release with improvements to 1.6.20. A little later, in June, version 1.7.0 was released with the Kotlin K2 compiler in Alpha for JVM, improved performance, and evolutionary changes related to the API. 

In September, incremental release 1.7.20 appeared. Here are some of its features:

• Kotlin K2 compiler with support for multiple compiler plugins;

• new language features;

• new Kotlin/Native memory manager (default);

• experimental feature for JVM with generic inline classes;

• support for Gradle 7.1.

We have considered the features of each language. Now it's time to compare them in terms of their main characteristics. 

Java vs. Kotlin for Android development: key feature comparison

Coroutine Support

This is the name of the tool which provides parallelism. The execution of one function can be suspended (the data are saved), and another function starts running. A program can perform several operations at the same time. This is one of its priority features of Kotlin. 

It allows multi-threading with little CPU resource consumption, which is valuable in mobile development. In Java, multiple threads are created to handle long operations, increasing the program code base. In its case, coroutine options such as Rx Java and Project loom may be available.

Null Safety

Anyone who works with Java comes across such an error message as a Null Pointer Exception. This happens if a line in the project refers to a variable with a null value. When it comes to a complex, large-scale project, finding such a line can take a long time. 

Kotlin solves this problem because all variables and objects are non-zero by default. If the line value is zero, the compiler stops building the project, which means that the error will not appear in the finished mobile app and will not create new problems for developers.

Operator Overloading

When any operator is used in the code, the function corresponding to it is called "behind the scenes." Each of these corresponds to a function with a specific name, for example, for "+," it would be "plus." With Kotlin, you can work with predefined sets of operators.

The language allows developers to overload operators and therefore use them as they see fit. At the same time, their set is limited. Each operator corresponds to a function name in a certain class. Functions for overloading are marked as "operator."

Wildcards

We are talking about special characters to replace other characters, such as "*" or "?". Kotlin has no such feature, unlike Java. Usually, the wildcard is a question mark, which indicates an unknown type. This is necessary to manage type safety when using generic types. 

Coding convention

This refers to a set of principles that recommend programming styles, methods, and practices for a program written in a particular language. Programmers must follow them to ensure that the code is readable and easy to maintain. 

In Java, these principles are prescribed by Oracle in the corresponding document. For example, you must use a camel case when defining classes, variables, and methods. Classes are capitalized nouns, and methods are imperative verbs with lowercase letters.

Kotlin offers many recommendations for source code organization, formatting, naming, etc. For example, the package name uses a lowercase letter and no underscore, and the class name uses a capital letter and camel case.

Data Classes

Their main purpose is to store and access data. When working with Java, you have to configure fields or variables and create functions such as constructor, getter, setter, etc. . This is more tedious than in Kotlin. 

The process is simplified by automation: just enter the keyword "data" in the class definition. The compiler automatically creates variables or fields.

Data type

For Java, types are divided into two large groups: primitive types (storing values) and reference types (storing an object address in memory). The first group includes integers, floating point numbers, and logical and character types. Reference includes all classes, arrays, interfaces, and String type. For Kotlin, the following are considered basic types: numbers, characters, lines, logical type, and arrays.

Documentation

Given the fact that Java is much older than its competitor, it is only natural to have a lot of documentation. This means code samples, manuals, tutorials, APIs, and more. All of this is freely available, allowing newcomers to immerse themselves in the technical nuances faster. 

Extension Functions

This is a striking feature of Kotlin, the essence of which is to add new functionality to certain types. It's quite easy to do: you just have to specify an extensible type as a prefix. With Java, it is not so simple. In other words, this useful feature is not available here. Extending the functionality of a class is done by creating a new class and inheriting functions from the parent class.

Functional Programming

Kotlin combines OOP and FP, where programs are written using function sets. The language can get the most out of using different types of functions. Anonymous functions or lambda expressions are also available with it. Java is limited to the concept of OOP, although lambda expressions have also been implemented in it since Java 8.

Performance

From this point of view, choosing Kotlin vs. Java for Android development is quite difficult. Both languages compile to similar bytecodes, so their performance does not seriously differ. It is much more important how clean and capacious the written code is. 

As we mentioned above, the "young" language is more compact, which has a positive impact on performance. But it has more additional features, which slow down the compilation and execution processes. 

Smart Casts

When it comes to type conversion, Kotlin provides useful features. First of all, the programmer can use the "is" operator to check an object against a given type. The compiler analyzes is-checks and is able to automatically insert ghosts where they are needed.

Speed of coding

With Kotlin, code is faster to work with due to its understandability. This reduces the likelihood of errors during the writing and compiling. Because of the brevity of the code, this language is easier to learn for beginners. In the case of Java, the coding structure is more complicated, and the code is several times longer. 

However, there is an important nuance. It takes a lot of time to find the best solution to a task in Kotlin. Yes, Java requires more code, but figuring out how to do the task is much faster.

Static members

These elements help to use some data independently of any object of this class. A static member is a common data member for all objects of this class. In Java, to declare a static data member, you must use the keyword "static." 

There are other differences related to different aspects of language usage. All of them will definitely be known to an experienced professional. Whichever option you choose, you should be sure that professionals will be working on the project. 

How much does it cost to develop an application in Java and Kotlin?

You can hire an offshore specialist to create a Kotlin vs. Java Android studio for a good cost. The main thing is to choose the region with the most attractive rates.

Java developer

As of December 2022, the average hourly rate for such a professional is $49.56. The minimum is $33, and the maximum is $270. If we calculate the median, we get $48. 

The most affordable prices are in Latin America (Uruguay – $51, Costa Rica – $50) and Eastern Europe (Romania – $51, Ukraine – $45). In Ukraine, Java ranks 3rd in the overall list of popular languages and 5th in mobile development.

Kotlin developer

According to the December update, the average hourly rate is $49.49. The minimum is $35, and the maximum is $150. The median is $50 per hour.

And again, we can highlight Latin America, this time Argentina with $50 and Brazil with $52. As for Eastern Europe, the most affordable rates are still in Romania ($49) and Ukraine ($44). In Ukraine, Kotlin is in 7th place by popularity and 2nd place by prevalence in mobile development.

As you can see, Eastern Europeans, namely Ukrainian developers, stand out in both cases. This is not surprising since Ukraine ranks 4th in the world in terms of IT outsourcing.

Still in doubt about whether to start developing in one of these languages? Perhaps you will be convinced by the successful experience of using them by world-famous companies.

The most famous applications written in Java and Kotlin

Let's start with Java as a more mature and widely used language. Here are a few companies that have achieved their goals with it:

• Spotify. Easier and faster API development.

• Twitter. Creating the ability to use it on a variety of devices.

• Cash App. Providing flexibility and security when dealing with bank accounts.

• LinkedIn. Processing for the server part of the app.

The benefits of Kotlin are appreciated by such well-known companies as:

• Tinder. Creation of concise and clear code architecture.

• Netflix. Rebuild the current UI player.

• Pinterest. Reducing application development time by migrating from Java to Kotlin.

• Uber. Faster and more productive mobile application development.

Each language gives the product certain advantages. It all depends on what you want your app to be and how quickly you want to bring it to market.

Conclusion

The battle of Kotlin vs. Java in Android development has been going on since the former was named by Google as a priority in this area. Perhaps every developer at least once has faced the difficulty of choosing between them to implement a mobile project. 

Java is time-tested and offers access to many libraries, frameworks, and documentation. Kotlin is more innovative; it has many useful features and is very easy to code. In the process of choosing, proceed from your goals and capabilities.