Kotlin vs Java: 15 Differences You Should Know

Browsing on the internet, you must have come across developers engaged in a heated debate about various programming languages. The topic of the discussion in this blog is between two programming languages, Kotlin or Java, and which of them is superior over the other. Before we go into which is superior or better than the other, it’s important to give you a quick rundown of their origin stories and history. So let’s get into it.

Java was created by Sun Microsystems in the 90s. Ever since then, it has been the go-to programming language for app developers. On the other hand, Kotlin is a rather recent addition. It was first released to the public back in 2011 by a firm named JetBrains. Ever since then, it has been steadily gaining popularity as well as the endorsement of various different developers.

Despite the fact that both languages are created to run on the JVM, there are a few key distinctions that can make it or break it for a developer or Android app development company, distinctions we’ll be covering in this Java vs Kotlin blog. So if you are a developer who is scratching their head on one to choose, then this blog is for you. 

Now let’s begin the Java vs. Kotlin debate by thoroughly going through what each language is, what features it entails, as well as the drawbacks programmers face when using it.

Java vs Kotlin: What is Java?

Starting off with Java, programming languages like Java adhere to the WORA principle. What does WORA mean though? Well, the term “write only, run anywhere,” or “WORA” for short, refers to the fact that programmers only need to write Java code once and may then execute it on any hardware or operating system that has a JVM installed. Now, you ask, what is a JVM? The Java bytecode, which is a condensed and portable representation of Java source code, that is interpreted and executed by a software layer is known as the JVM, or Java Virtual Machine.

As a statically typed language, Java has a fixed data type for each variable and statement, which is verified at compile time. This facilitates error-free code compilation for Android developers and helps enhance the runtime performance of the application.

In addition, Java is also an object-oriented language (OOL), which means that it divides information and behavior into classes and objects that can communicate with one another via encapsulation, polymorphism, and inheritance.

Features of Java

We’ve gone ahead and listed below all the features that come with using Java to code and create applications.

• Java supports a variety of programming paradigms such as imperative, declarative, functional, and concurrent.
• Java has a wide range of native data types, including primitives, arrays, strings, collections, and streams.
• It provides a wide range of utilities, including input and output, networking, database access, concurrency, security, and testing, through a standard library.
• Java has a strong exception handling mechanism that enables you to gracefully manage mistakes and failures.
• Enables you to develop more expressive and condensed code by providing robust support for generics, annotations, lambda expressions, and streams.
• Has a strong concurrency model that enables the development of multithreaded programs that make use of several processors and cores.
• Has a high-performance garbage collector that takes care of memory deallocation and allocation automatically.
• Have access to a variety of frameworks and tools that can aid you in the creation of apps, including IDEs, testing tools, debugging tools, build tools, dependency management tools, web frameworks, and more.

Drawbacks of Java

Not everything that glitters is gold. Here are some downsides to utilizing Java that you can (potentially) encounter.

• It forces you to create A LOT of boilerplate code. Why? Because of its verbose syntax when doing routine activities.
• Sadly Java does not support some contemporary features like null safety, extension functions, data classes, and coroutines that are accessible in other languages like Kotlin.
• Its architecture has various restrictions and flaws, including the absence of multiple inheritance, the distinction between primitive and reference types, and the lack of operator overloading.
• Its dynamic nature and dependence on the JVM has been reported to cause performance problems.
• Because of its complicated governance mechanism and needs for backward compatibility, Java has a somewhat lengthy evolution process.

Java vs Kotlin: What is Kotlin?

Just like Java, Kotlin too is a programming language, but one that is made to be a superior substitute or alternative. It is an object-oriented, general-purpose language that can operate on the JVM, just like Java. But what distinguishes it as a superior choice? Well for starters, its support for other platforms including Android, iOS, JavaScript, and native code?

Despite being statically typed, Kotlin also offers type inference. This implies that developers are not required to explicitly identify the data type of each variable and expression. Based on the context and the value assigned to the variable, the compiler can determine the data type.

Although Kotlin enables functional programming, it is also an object-oriented language. What does that result in? The functions in Kotlin are treated as first-class constructs and can be passed as arguments, returned by functions, and stored in variables. Additionally, Kotlin has support for closures, lambdas, and higher-order functions, enabling programmers to be more compact and expressive when writing code.

Features of Kotlin

In this section, we’ve discussed all the features that come with using Kotlin as your desired programming language.

• Because of the clear and expressive syntax Kotlin boasts, it requires much less boilerplate code and makes programming much, much easier to read for programmers.
• Kotlin has significant support for null safety, which implies that by recognizing nullable and non-nullable types, it avoids null pointer exceptions altogether.
• Extension functions, a potent feature of it, lets you extend the functionality of existing classes without changing their source code or deriving from them.
• Kotlin features a useful function called data classes that lets you make classes that solely contain data and automatically generates methods like equals, hashCode, toString, copy, etc.
• Coroutines, a revolutionary feature of it, let you create asynchronous, non-blocking code in a sequential, synchronous manner.
• Primitives, arrays, strings, collections, ranges, sequences, and other built-in data types are only a few examples of the extensive collection it has.
• Various utilities, including input/output, networking, database access, concurrency, serialization, reflection, etc., are provided via its extensive standard library.
• You can use any Java library or framework in Kotlin code and vice versa because it seamlessly interoperates with Java.
• It has a quick and intelligent compiler that carries out a number of optimizations and checks for faults and warnings during compilation.
• It has a thriving community that offers a range of frameworks and tools that can assist you with many parts of software development, including IDEs, testing tools, debugging tools, build tools, dependency management tools, web frameworks, microservices frameworks, etc.

Drawbacks of Kotlin

Now, let’s go through the cons of using Kotlin as your programming language.

• For novice developers who are unfamiliar with its syntax and functionality, Kotlin has a relatively steep learning curve compared to Java.
• Kotlin has some difficulty working with various Java frameworks and libraries that depend on reflection or annotations.
• Because of the use of inline functions and lambdas, which produce additional bytecode and expand the executable file overall, Kotlin reportedly has (to some degree) speed difficulties.
• Kotlin has a lengthy analysis and optimization procedure which slows down compilation speed. For example, Java is 15-20% faster in clean compilations without Gradle.
• Kotlin has a less developed and stable ecosystem than Java, mostly because it is more recent.

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Why compare Java and Kotlin?

Despite the fact that they both have numerous similarities and differences, comparing them side by side can help developers better understand, assess, and evaluate their strengths and shortcomings. This will enable developers to weigh their options and select the one that is best for a particular project, and the end debate between Java vs Kotlin, once and for all.

That being said, if you’re comparing Java vs Kotlin, one or more of the following reasons might apply to you:

• You are a Java developer who wants to move to Kotlin for your upcoming project or study Kotlin.
• You are a Kotlin developer who wishes to learn Java or incorporate Java frameworks or libraries into your Kotlin projects.
• You’re a beginner looking to pick your first programming language, and you’re torn between Java and Kotlin.
• The language you choose for your project may depend on a number of factors, including performance, productivity, maintainability, and scalability, and whether you’re a project manager or team leader.

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Java vs Kotlin (15 Differences)

To put it simply, there is no clear winner in the Java vs Kotlin argument. Depending on the situation and use case, each language has a specific set of advantages and disadvantages. Therefore, the only way we can properly capture and appreciate their differences is by comparing them on the basis of numerous distinct variables, such as syntax, features, performance, community support, etc.

In order to provide a more accurate comparison of Kotlin vs Java, we will shed light on Kotlin vs Java code comparison in this blog post, in totality 15 key differences. These distinctions are intended to be indicative and instructive rather than exhaustive or conclusive. In light of this, we advise you to conduct your own study and testing before settling the Kotlin vs Java argument.

1. Kotlin vs Java Syntax

Starting of the Kotlin vs Java debate is “syntax”. Syntax refers to the rules and structure of a language that defines how to write and format the code, where one of the most noticeable differences between Java and Kotlin lies. Syntax can affect the readability, maintainability, and productivity of the code in question.

Java boasts a verbose and rigid syntax that requires you to write a lot of boilerplate code, even for common tasks. Let’s put it into perspective, you need to declare the data type of every variable and expression, use semicolons to end every statement, use parentheses and curly braces to enclose every block of code, use keywords such as public, static, final, etc. to specify the modifiers and attributes of every class, method, and variable, etc.

public class Person {

    private String name;

    public Person(String name) {

        this.name = name;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

Kotlin on the other hand, has relatively concise and flexible syntax that enables you to write much less code to achieve the same level functionality. For example, you can omit the data type of variables and expressions if the compiler can infer it from the context, use line breaks instead of semicolons to separate statements, use indentation instead of curly braces to define blocks of code, use modifiers and attributes only when necessary or when they differ from the default values.

data class Person(val name: String)

The succinct syntax of Kotlin enables developers to write cleaner and more maintainable codebases.

2. Null Safety

Null safety is another important difference between Java and Kotlin. It refers to the ability of a language to prevent or handle NPEs aka NullPointerExceptions (which are runtime errors that occur when you try to access or manipulate a variable or an object that has a null value).

Java currently does host a built-in mechanism to prevent or handle NPEs, as such, require you to manually check for null values before using any variable or object (that might be null). Why is this bad? When using Java and you make a mistake in your logic, you’ll probably end up with an NPE that crashes your application entirely.

String name = null;

// …

int length = name.length(); // Throws NullPointerException

Kotlin on the other hand has a built-in mechanism that helps prevent or handle NPEs. It distinguishes between nullable and non-nullable types by using a question mark (?) after the data type. A nullable type can hold a null value, while a non-nullable type cannot. The compiler checks for null values at compile time, enabling you to prevent using any variable or object that might be null without proper handling.

var name: String? = null

// …

val length = name?.length // No exception; length will be null if name is null

Kotlin’s null safety forces developers to be explicit about null handling, reducing the overall risk of NPEs in the code.

3. Type Inference

Java requires developers to explicitly specify the data type of variables, which can result in more verbose code.

String name = “John”; // Type specified explicitly

In contrast, Kotlin leverages the use of powerful type inference, which allows the compiler to determine the variable’s data type automatically.

val name = “John” // Type inferred automatically as String

Why is this beneficial? In short, it leads to more concise and readable code in Kotlin.

4. Extension Functions

Another interesting difference between Java and Kotlin lies in extension functions. For those of you who don’t know, extension functions are a feature that allows you to add new functionality to existing classes without modifying their source code or inheriting from them.

Java does not have support for extension functions. To use them, you have to either modify the source code of the class that you want to extend (which is not usually possible or at the very least desirable) or create a subclass that inherits from the class that you want to extend. This can introduce unnecessary complexities or overheads.

// Utility class example

public class StringUtils {

    public static String reverseString(String input) {

        // …

    }

}

String reversed = StringUtils.reverseString(“Hello”);

Unlike Java, Kotlin supports extension functions which helps improve code organization and readability by grouping related functions with the extended class. This can enable you to define an extension function by using the dot (.) notation after the class that you want to extend and then specifying the function signature and body. You can then call the extension function on any instance of the class that you extended as if it was a member function.

// Extension function example

fun String.reverse(): String {

    // …

}

val reversed = “Hello”.reverse()

5. Data Classes

Creating data classes in Java requires writing boilerplate code for constructors, getters, setters, equals(), hashCode(), and toString() methods.

public class Person {

    private String name;

    private int age;

    // Constructors, getters, setters, equals(), hashCode(), and toString() methods

    // …

}

As Kotlin introduces data classes, it helps significantly reduce the amount of boilerplate code required for the same function compared to Java.

data class Person(val name: String, val age: Int)

Kotlin automatically generates the equals(), hashCode(), and toString() methods for data classes, making them much more convenient to be used by developers.

6. Smart Casts

Java does not support smart casts and requires explicit type casting in certain scenarios. Type casting refers to changing a variable of one data type into another.

Object obj = “Hello”;

if (obj instanceof String) {

    String message = (String) obj; // Explicit type casting

}

Compared to Java, Kotlin supports smart casts, which in turn, enables automatic type casting based on certain conditions.

val obj: Any = “Hello”

if (obj is String) {

    val message: String = obj // Automatic type casting

}

Support for smart casts in Kotlin enables developers to further simplify code while eliminating the need for repetitive type checks.

7. Collection Operations

Java uses external iteration, where developers need to explicitly manage the iteration process.

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

for (int i = 0; i < numbers.size(); i++) {

    int number = numbers.get(i);

    // …

}

Kotlin on the other hand enables developers to provide a more concise and expressive approach with internal iteration using higher-order functions.

val numbers = listOf(1, 2, 3, 4, 5)

numbers.forEach { number ->

    // …

}

Kotlin’s collection operations lead to more readable and expressive code.

8. Functional Programming

Java offers its developers support for functional programming through the use of libraries like Stream API, but it lacks native functional features.

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

int sum = numbers.stream().mapToInt(Integer::intValue).sum();

Compared to Java, Kotlin embraces functional programming concepts natively, providing features such as lambda expressions and higher-order functions.

val numbers = listOf(1, 2, 3, 4, 5)

val sum = numbers.sum()

Kotlin’s native functional support enables the generation of concise and expressive code for various operations.

9. Coroutines vs Threads

Java uses traditional threads for concurrent programming, which can be error-prone and lead to issues like thread starvation and deadlocks.

Runnable task = () -> {

    // …

};

Thread thread = new Thread(task);

thread.start();

Kotlin introduces coroutines, which are lightweight, asynchronous, and provide safer concurrency.

val task = {

    // …

}

GlobalScope.launch(Dispatchers.Default) {

    task()

}

Coroutines in Kotlin help simplify concurrent programming and make it easier to handle asynchronous tasks.

10. Interoperability

Java and Kotlin are designed to work together seamlessly, allowing developers to mix and match both languages within the same project.

// Java code

public class JavaClass {

    // …

}

// Kotlin code

class KotlinClass {

    // …

}

// Using Java class in Kotlin

val javaObject = JavaClass()

Kotlin can call Java code just like any other Kotlin code, ensuring a smooth transition for developers.

// Using Kotlin class in Java

KotlinClass kotlinObject = new KotlinClass();

11. Kotlin vs Java for Android App Development

Let’s move onto kotlin vs java for android development.

Java has been the traditional go-to language for app development in Houston for many years.

1. Adoption and Future Trends of Kotlin vs Java

public class MainActivity extends AppCompatActivity {

    // …

}

Now, since the advent of Kotlin, developers have started using it for Android app development as it helps provide a much more modern and concise syntax, making the entire coding process for developers much more enjoyable and simpler.

class MainActivity : AppCompatActivity() {

    // …

}

Kotlin boasts a plethora of features, such as null safety and extension functions, all of which drastically improve and streamline the Android app development process, efficiency, and overall code quality.

12. Learning Curve of Java vs Kotlin

The learning curve for any new language is an important factor to take into consideration for developers.

Java’s syntax and concepts are well-established, making it relatively easier for developers that are already familiar with C++-like languages. And since Java has been around for many years, there is a lot of documentation, support, and community forums for development related insights.

Although Kotlin’s syntax is much more expressive and concise, developers with a background in Java may face a bit of a learning curve before completely transitioning over to Kotlin.

13. Kotlin vs Java Performance

Performance is a critical factor for any application.

Java based applications are highly optimized for performance as the language has been reiterated and refined over the years.

Now Kotlin compiles on Java bytecode and runs on the Java Virtual Machine (JVM), making its performance more or less similar to Java. In short, solely comparing Java and Kotlin in terms of performance, they are at a stalemate.

14. Community and Support

The size and activity of the developer community impact mass language adoption and support.

Since Java already has a massive and well-established community with extensive documentation and support, it gives it an edge over Kotlin in this particular aspect.

Kotlin, although a relatively new language, its community is growing rapidly, especially since it has garnered strong support from JetBrains and Google.

15. Adoption and Future Trends of Kotlin vs Java

The adoption rate and future trends of a language can influence its long-term viability.

Java’s widespread adoption ensures its continued relevance in the software development landscape.

Kotlin’s rising popularity, especially in the Android app development domain, suggests and is forecasting a promising future for the language.

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Conclusion

To sum it all up, Java and Kotlin are both powerful programming languages, each boasting its own unique set of features, strengths, and drawbacks. Java has stood the test of time and remains a solid choice for traditional enterprise applications. On the other hand, Kotlin’s modern and expressive syntax, along with its features like null safety, extension functions, and coroutines, make it an excellent choice for Android app development and projects seeking enhanced productivity and code readability.

Whenever you find yourself deciding between Java and Kotlin, take into consideration your project’s unique requirements, team familiarity, and long-term goals. Both languages offer remarkable compatibility, allowing you to leverage the best of both worlds. Whether you are building large-scale enterprise applications or innovative mobile apps with the help of a custom mobile app development company, Java and Kotlin have proven to be reliable and effective choices in the ever-changing landscape of software development.

FAQs

Q: Is Kotlin fully interoperable with Java? 

A: Yes, Kotlin is fully interoperable with Java, allowing seamless integration of both languages within the same project.

Q: Does Kotlin run on the Java Virtual Machine (JVM)? 

A: Yes, Kotlin compiles to Java bytecode and runs on the JVM, ensuring compatibility with existing Java code and libraries.

Q: What are some benefits of using Kotlin over Java? 

A: Kotlin offers benefits such as null safety, concise syntax, extension functions, and native support for functional programming.

Q: Can I use Kotlin for Android app development? 

A: Yes, Kotlin is an official language for Android app development and is widely used in the Android community.

Q: Are there Kotlin vs Java differences in performance?

A: Kotlin compiles to Java bytecode and performs comparably to Java in terms of performance. Performance differences, if any, are negligible for most applications.