Kotlin vs Java

Are you embarking on a new Android development project and unsure whether to choose Kotlin or Java? You’ve come to the right place. This guide provides a comprehensive comparison of Kotlin vs Java, helping you make an informed decision.

We will begin with an introduction to both languages, highlighting their unique features, key differences, and strengths. Additionally, we will offer insights on how to select the best language based on your specific project requirements.

Are you ready? Let’s dive in and get started!

Kotlin vs Java Summary

Before diving into the in-depth comparison of Kotlin vs Java, let’s explore a quick summary to get an overview of the key differences and similarities between these two programming languages. I have created a table comparing Java and Kotlin for your benefit.

What is Java?

Java, introduced in 1995, was created by James Gosling at Sun Microsystems, which later became part of Oracle in 2009. It is an open-source, general-purpose programming language designed with object-oriented principles. 

Being a multiplatform language, Java can operate on various devices, operating systems, and servers. This versatility is achieved through compilation to bytecode, which allows the code to run on any Java Virtual Machine (JVM).

Java uses a static typing system, meaning type checking occurs at compile time. Its syntax is influenced by C and C++ but excludes many lower-level features, making it a higher-level and more streamlined language.

What is Kotlin?

Kotlin, introduced in 2016, is a modern open-source programming language. Like Java, it compiles to bytecode and runs on the Java Virtual Machine (JVM), making it compatible with a wide range of platforms. 

Additionally, Kotlin seamlessly integrates with Java, allowing the use of Java libraries and frameworks within Kotlin projects.

While influenced by Java, Kotlin is designed to be a more concise, cleaner, and faster-compiling alternative. It combines the principles of object-oriented and functional programming to create a versatile and efficient coding experience.

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Why Compare Kotlin and Java?

You may be wondering, why compare Java and Kotlin?

Java is a widely-used general-purpose programming language and is considered one of the most popular languages globally, alongside JavaScript and Python. While Kotlin may not yet compete for the same level of global popularity, it has emerged as a strong contender in the field of Android development.

According to the 2024 Stack Overflow Developer Survey, 9.4% of all respondents used Kotlin as part of their development. Meanwhile, Java still commanded a 30.3% share.

In 2017, just a year after its release, Google designated Kotlin as the second official language for Android development. By 2019, Google further elevated Kotlin by declaring it the preferred language for Android applications. This recognition has driven Kotlin’s rapid adoption and growth within the Android development community.

Given this context, understanding the differences between Kotlin and Java is essential to making the best choice for your development needs.

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Java Issues Addressed in Kotlin

Before exploring their differences, it’s important to first understand some of the key issues in Java that Kotlin effectively addresses. 

Kotlin resolves several challenges commonly associated with Java:

• Null Safety: Null references are managed by Kotlin’s type system, reducing the risk of null pointer exceptions.
• No Raw Types: Kotlin eliminates the use of raw types, ensuring stronger type safety.
• Invariant Arrays: Arrays in Kotlin are invariant, preventing issues with type variance.
• Proper Function Types: Kotlin supports proper function types, unlike Java’s SAM (Single Abstract Method) conversions.
• Use-Site Variance Without Wildcards: Kotlin simplifies variance handling without relying on wildcards.
• No Checked Exceptions: Kotlin does not include checked exceptions, reducing boilerplate code.
• Separate Interfaces for Collections: Kotlin distinguishes between read-only and mutable collections with separate interfaces, enhancing clarity and usability.

What Java Has that Kotlin Does Not

While Kotlin offers many advantages, Java still retains some key features that are not present in Kotlin. Let’s explore a few of these unique aspects.

Kotlin omits some features found in Java, including:

• Checked Exceptions: Kotlin does not support checked exceptions, simplifying exception handling but reducing compile-time error checking.
• Primitive Types as Classes: While Kotlin uses primitive types in bytecode where possible for efficiency, they are not explicitly available as in Java.
• Static Members: Kotlin replaces static members with alternatives like companion objects, top-level functions, extension functions, or the @JvmStatic annotation.
• Wildcard Types: Java’s wildcard types are replaced in Kotlin by declaration-site variance and type projections.
• Ternary Operator: Java’s ternary operator (a ? b : c) is replaced in Kotlin by the more readable if expression.
• Records: Kotlin does not have records, a feature introduced in Java for immutable data objects.
• Pattern Matching: Java’s pattern matching capabilities are not directly available in Kotlin.
• Package-Private Visibility: Kotlin lacks the package-private visibility modifier found in Java.

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What Kotlin Has that Java Does Not

Kotlin is a modern, more concise alternative to Java, and while it can be used for many of the same things as Java, it has a particular focus on improving the developer experience. Therefore, it has many features not available in Java. 

Kotlin introduces several features not available in Java, including:

• Lambda Expressions with Inline Functions: Enable performant custom control structures.
• Extension Functions: Add new functionality to existing classes without modifying their code.
• Null Safety: Reduces runtime null pointer exceptions by managing nullability at the type level.
• Smart Casts: Automatically cast variables after type checks (similar to Java 16’s pattern matching for instanceof).
• String Templates: Simplify string manipulation by embedding expressions directly within strings (introduced as a preview feature in Java 21).
• Properties: Replace boilerplate getter and setter methods with a more concise syntax.
• Primary Constructors: Simplify object instantiation with a compact declaration.
• First-Class Delegation: Provides a straightforward mechanism for delegation without boilerplate.
• Type Inference: Automatically determines variable and property types (similar to Java 10’s local-variable type inference).
• Singletons: Simplified singleton pattern support.
• Declaration-Site Variance and Type Projections: Manage generics more intuitively compared to Java’s use-site variance.
• Range Expressions: Easily represent ranges of values.
• Operator Overloading: Customize operators for specific use cases.
• Companion Objects: Serve as a replacement for static members.
• Data Classes: Simplify the creation of classes meant to hold data by generating common functions automatically.
• Coroutines: Support asynchronous programming with a concise syntax and better control.
• Top-Level Functions: Eliminate the need for utility classes by allowing functions to exist outside a class.
• Default Arguments and Named Parameters: Improve function call readability and flexibility.
• Infix Functions: Enable more readable function calls by omitting dots and parentheses.
• Expect and Actual Declarations: Facilitate multiplatform development by separating platform-specific code.
• Explicit API Mode: Provides better control over the API surface, ensuring clarity in public-facing code.

In-Depth Guide: How to Hire Kotlin Developers ➜

Differences Between Kotlin and Java

Curious about the main differences between Java and Kotlin? In this section, we will explore the key distinctions that set these two languages apart.

Here are 12 Key Differences between Kotlin and Java:

1. Syntax
2. Null Safety
3. Functional Programming
4. Code Differences
5. Coroutines Support
6. Data Classes
7. Smart Casts
8. Checked Exceptions
9. Primitive Types
10. Public Fields
11. Wildcard Types
12. Implicit Conversions

Kotlin and Java: Syntax Comparison

One of the key differences between Kotlin and Java is their syntax. Kotlin provides a more concise and readable syntax, requiring less code to achieve the same functionality as Java.

Example: Defining a Class

Here’s a comparison of how you create a simple class in both languages:

Java:

public class MyClass {

   private int myField;

   public MyClass(int myField) {

      this.myField = myField;

   }

   public int getMyField() {

      return myField;

   }

   public void setMyField(int myField) {

      this.myField = myField;

   }

}

Kotlin:

class MyClass(private var myField: Int) {

   fun getMyField() = myField

   fun setMyField(value: Int) { myField = value }

}

Key Observations:

• The Kotlin code is much shorter and more intuitive.
• In Kotlin, you can define a class and its fields in a single line.
• Getters and setters in Kotlin are replaced by property accessors, which streamline the code.

Example: Type Inference

Kotlin supports type inference, meaning you don’t have to explicitly specify a variable’s data type. The compiler determines it based on the assigned value.

Kotlin:

val myString = "Hello, world!"

Java:

String myString = "Hello, world!";

Key Observations:

• Kotlin eliminates the need for explicit type declarations, making the code cleaner.
• In Java, you must always specify the variable’s data type, resulting in more verbose code.

Example: “Hello, World!” Program

Even in a basic program, Kotlin’s simplicity stands out.

Java:

public class HelloWorld {

    public static void main(String[] args) {

        System.out.println("Hello, World!");

    }

}

Kotlin:

fun main() {

    println("Hello, World!")

}

Kotlin vs. Java: Null Safety

While both Kotlin and Java run on the JVM and offer similar performance characteristics, Kotlin introduces features that can improve performance and reliability. One of these key features is null safety, which reduces the chances of runtime errors and improves overall application stability.

Null Safety in Java

In Java, variables can hold null values unless specifically managed otherwise. This flexibility can lead to NullPointerExceptions (NPEs) if null values are used improperly during runtime.

Java Example:

String name = null; // This could cause a NullPointerException if used without checks

Null Safety in Kotlin

Kotlin enforces null safety by requiring you to explicitly declare whether a variable can hold null values. By default, all variables in Kotlin are non-nullable, meaning they cannot hold null unless explicitly defined as nullable using the ? operator.

Kotlin Example:

var name: String = "John" // Non-null variable; cannot hold null

var age: Int? = null      // Nullable variable; can hold null

Key Benefits of Kotlin’s Null Safety:

1. Compile-Time Checks: Null-related issues are caught during compilation, reducing the risk of runtime crashes.
2. Improved Code Clarity: Developers explicitly define nullable variables, making the code more readable and predictable.
3. Reduced Runtime Exceptions: Fewer null pointer exceptions lead to more stable applications.

Kotlin vs Java: Functional Programming

One of the key differences between Kotlin and Java is their approach to functional programming. While Java introduced limited support for functional programming with Java 8, Kotlin was designed with functional programming concepts at its core, offering more seamless and expressive tools.

Key Functional Programming Features in Kotlin

Kotlin provides powerful functional programming features that help make code more concise, expressive, and easier to maintain. These include:

1. Lambda Expressions: Compact functions that can be defined inline.
2. Higher-Order Functions: Functions that can take other functions as parameters or return functions as results.
3. Extension Functions: Functions that allow you to add new methods to existing classes without modifying them.

Example of Functional Programming Features in Kotlin

// Lambda Expressions

val list = listOf(1, 2, 3)

val doubledList = list.map { it * 2 } // Doubles each element in the list

// HIgher-Order Functions

fun higherOrderFunc(x: Int, y: Int, f: (Int, Int) -> Int): Int {

    return f(x, y)

}

val result = higherOrderFunc(3, 4) { x, y -> x + y } // Adds 3 and 4 using a lambda

// Extension Functions

fun Int.isEven() = this % 2 == 0 // Adds an 'isEven' method to the Int class

val isFourEven = 4.isEven() // Checks if 4 is even

Kotlin vs Java: Code Differences

A major distinction between Kotlin and Java lies in Kotlin’s conciseness. Kotlin requires significantly less code than Java, reducing complexity and minimizing the likelihood of errors, which makes development more efficient.

Kotlin’s conciseness is particularly advantageous for larger projects, as it enables developers to write the same functionality in fewer lines of code compared to Java. Despite its compact nature, Kotlin maintains clear and readable syntax, ensuring code remains easy to understand and manage.

Kotlin vs Java: Coroutines Support

In Android development, components typically run in the same process and thread, known as the main thread, which is responsible for the user interface (UI). Operations like network I/O and CPU-intensive tasks can take a long time to complete, blocking the calling thread until they finish.

In Java, to avoid blocking the main thread, developers create multiple background threads to handle these lengthy operations. However, managing multiple threads can be complex and error-prone.

Kotlin offers a more efficient solution with coroutines. Unlike traditional threads, coroutines are stackless and allow developers to suspend and later resume execution without blocking the main thread. This approach enables non-blocking, asynchronous code that behaves like synchronous code.

By using coroutines, developers can avoid the complexities of managing multiple threads while writing cleaner, more concise code compared to Java’s thread-based solution.

Kotlin vs Java: Data Classes

In Java, developers must manually define the fields (or variables) to store data, along with a constructor, getter and setter methods, and additional functions like hashCode(), equals(), and toString(). These classes are primarily designed to store data with minimal functionality.

In contrast, Kotlin simplifies the process by allowing developers to create data-holding classes with ease. By adding the data keyword to the class definition, Kotlin automatically generates the constructor, along with getter and setter methods for the fields. This reduces the amount of boilerplate code and streamlines the creation of data classes.

Kotlin vs Java: Smart Casts

In Java, developers must manually check an object’s type before performing a cast, ensuring it aligns with the intended operation.

Kotlin simplifies this process with smart casts. Using the is keyword, Kotlin’s intelligent compiler automatically handles type checks and eliminates the need for redundant casts when the value is stable. This feature streamlines code and reduces the likelihood of errors.

Kotlin vs Java: Checked Exceptions

Kotlin does not support checked exceptions, meaning developers are not required to catch or declare exceptions. Whether this is an advantage or disadvantage depends on the perspective.

In Java, checked exceptions force developers to either catch or declare exceptions. While this can be frustrating and time-consuming, it also promotes more robust code by ensuring that errors are explicitly handled. Ultimately, the choice between the two approaches depends on what developers prioritize: simplicity or thorough error handling.

Kotlin vs Java: Primitive Types

In Java, primitive types are not objects but predefined data types. Java has eight primitive types: int, byte, short, double, float, boolean, char, and long. These variables cannot be treated as objects or represented by a class or struct.

While primitive types themselves are not classes, Java provides wrapper classes (such as Integer for int) to wrap primitive values as objects. However, developers must explicitly use these wrapper classes when needed.

In contrast, Kotlin automatically treats variables of primitive types as objects, streamlining the process and eliminating the need for explicit wrapper classes.

Kotlin vs Java: Public Fields

In Java, public fields (also known as non-private fields) are accessible, allowing callers to modify them directly. This can be convenient because it enables developers to change the internal representation of an object without needing to modify the callers. By keeping fields public, the public API remains unchanged, helping to maintain the program.

In contrast, Kotlin does not support public fields. Instead, Kotlin encourages the use of properties with proper access control, promoting better encapsulation and code structure.

Kotlin vs Java: Wildcard Types

In programming, a question mark (?) is often used as a wildcard, representing an unknown type (such as a variable, field, or parameter).

Kotlin does not support wildcard types like Java. Instead, Kotlin uses declaration-site variance and type projections as alternatives to handle type flexibility.

Kotlin vs Java: Implicit Conversions

Kotlin does not support implicit widening conversions, meaning smaller types cannot automatically be converted to larger types. Developers must explicitly perform type conversions to achieve the desired result.

In contrast, Java allows implicit conversions, where smaller types can be automatically converted to larger types without requiring explicit intervention from the developer.

Kotlin vs Java: Which is Better?

Kotlin and Java each have their own strengths, making the choice between them dependent on the specific needs of your project. First up, Kotlin is a more modern language with concise syntax, null safety, and is officially supported by Google for Android development. Java, on the other hand, boasts a larger ecosystem, mature tools, and an extensive library base.

Despite their differences, both Kotlin and Java compile to bytecode, meaning you can easily mix Kotlin and Java code within the same project.

Kotlin offers several advantages, especially in Android development, including:

• Requires less code
• Faster compilation and lightweight deployment
• Supports coroutines for efficient asynchronous programming
• Fully compatible with Java libraries and frameworks
• Eliminates the risk of NullPointerException through null safety

However, Java also has notable benefits:

• Promotes robust, well-structured coding
• Supports a wide range of platforms, servers, operating systems, and devices
• Forms the foundation of Android development
• Has been around longer, providing a large community, comprehensive documentation, and a vast ecosystem of libraries and tools

Ultimately, the choice between Kotlin and Java depends on the specific requirements of your project.

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Kotlin vs Java: Choosing the Right Language

After considering the benefits of both Kotlin and Java, it may seem difficult to choose the right one. Let’s take a practical approach to help guide the decision.

Kotlin has quickly gained popularity, especially in Android development. Its success stems from features that greatly enhance developer productivity, such as extension functions, lambda expressions, higher-order functions, coroutines, and null safety (eliminating NullPointerExceptions).

These features make it clear that Kotlin is a strong contender for Android development and is likely to dominate the field in the future.

Is Kotlin Replacing Java?

While Kotlin is becoming the preferred choice for many developers, Java still holds significant value and should not be overlooked. For general-purpose programming, Java remains a powerful and widely used language. Even in Android development, Java continues to be an excellent option, and it’s understandable why some developers still prefer it.

Ultimately, the decision depends on the development team’s expertise and which language they feel most comfortable with. Java has been a popular language for many years, and while Kotlin is on the rise, it’s unlikely that Java will be completely replaced anytime soon.

Conclusion

In summary, both Kotlin and Java are powerful programming languages, each with its own strengths and distinctions. While Java is a well-established language with a large community and an extensive library ecosystem, Kotlin offers modern features and a more concise syntax, making it an appealing choice for many developers.

For Android development, Kotlin currently stands out as the preferred option. Its adoption is growing rapidly among developers and companies, and it is likely to continue expanding its presence in the Android ecosystem.

However, Java remains an excellent general-purpose language. Having been the foundation of Android development for years, it will not be phased out quickly.

Two things are certain:

1. Java is here to stay and will continue to be a core part of the development landscape for the foreseeable future.
2. Kotlin, on the other hand, is gaining momentum, becoming more developer-friendly, and attracting major companies like Atlassian, Pinterest, Basecamp, and Coursera, all of which have adopted Kotlin for their mobile apps.

Ultimately, the debate over Kotlin vs Java, and which language is “better” is not straightforward and will likely spark continued discussions. There are many factors to consider beyond the languages’ differences, such as the technologies employed by companies and the level of comfort developers have with Kotlin or Java.

Kotlin vs Java FAQs

In this section, let’s explore some of the Frequently Asked Questions (FAQs) related to Kotlin vs Java. If you want further clarification, feel free to comment in the comments section at the end of the article. 

Should I choose Kotlin over Java for a new project?

The choice between Kotlin and Java largely depends on the specific needs of your project and your personal preferences as a developer. 

Kotlin is ideal for new projects that prioritize efficient development, modern features, and concise code. 

Java, on the other hand, is better suited for projects that require robust stability, long-term support, and a large ecosystem of mature tools and libraries.

What are the differences between Java and Kotlin?

Kotlin is a more modern language, offering concise syntax, null safety, and official support from Google for Android development. Java, while older, boasts a larger ecosystem with mature tools and libraries. The “better” language for your project depends on your specific requirements, including factors like development speed, performance, and the complexity of the project.

Should I learn Kotlin or Java first and why?

You do not need to master Java before learning Kotlin. While understanding Java can be helpful, especially for converting between the two languages, Kotlin is designed to be easy to learn, even without prior Java knowledge. 

In fact, Kotlin can make life easier for Java developers by reducing boilerplate code and simplifying common tasks. However, many Android tutorials and examples still use Java, so familiarity with Java can be beneficial for certain Android development contexts.

What are the advantages of Kotlin?

Kotlin offers several advantages, including:

• Concise syntax: Kotlin reduces boilerplate code compared to Java, making it easier to read and write.
• Null safety: Kotlin’s type system helps prevent null pointer exceptions, a common source of errors in Java.
• Modern features: Kotlin includes features like extension functions, coroutines, and data classes, which enhance productivity.
• Interoperability: Kotlin works seamlessly with existing Java code, libraries, and frameworks, making integration easy.
• Android development: Kotlin is the preferred language for Android development, as declared by Google.

What are the advantages of Java?

Java also offers numerous advantages, such as:

• Established ecosystem: Java has a vast ecosystem of libraries, frameworks, and tools, making it suitable for a wide range of projects.
• Performance: Although Kotlin is catching up, Java may offer slightly better performance in some scenarios.
• Community: Java has a larger and more established community, which makes it easier to find support and resources.
• Legacy projects: Many existing projects are written in Java, meaning Java is still essential for maintaining and extending these applications.

Is Kotlin better than Java?

Kotlin is often considered “better” than Java for many modern development tasks due to its more concise syntax, null safety, and modern features like extension functions and coroutines. However, Java remains a strong choice due to its extensive ecosystem, community, and stability, especially for large, legacy systems.

Is Kotlin going to replace Java?

Kotlin is unlikely to fully replace Java, but it is becoming the preferred language for Android development and is gaining traction in other areas as well. Java will continue to be widely used, particularly in enterprise, backend, and legacy projects.

Can Kotlin do everything Java can?

Yes, Kotlin can perform all the tasks Java can, as it is fully interoperable with Java and runs on the JVM. Kotlin enhances Java’s capabilities with modern features, but it doesn’t limit the ability to do anything Java can do.

Is Kotlin hard if you know Java?

Kotlin is relatively easy to learn if you already know Java. It offers many similar concepts but simplifies syntax and introduces new features. The transition from Java to Kotlin is generally smooth, and Java developers often find Kotlin to be a more concise and expressive language.

How close is Kotlin to Java?

Kotlin and Java are very close in terms of functionality, as Kotlin runs on the JVM and is fully interoperable with Java. The key differences lie in Kotlin’s more modern syntax and language features, but the two languages can coexist within the same project without issues.

What is the performance of Kotlin vs Java?

Kotlin’s performance is comparable to Java’s because both languages run on the JVM and compile to bytecode. In most cases, Kotlin’s performance is nearly identical to Java’s, though some minor differences may exist due to Kotlin’s additional language features like null safety and extension functions.

This page was last edited on 19 December 2024, at 10:32 am