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Kotlin Vs Java: The Major Differences That You Should Be Aware Of!

Aug, 2022

Which language do you prefer for Android development: Kotlin vs Java? This article will discuss the major distinctions between the two programming languages. Following that, we’ll debate over Kotlin vs Java, which one is superior, and highlight the primary reasons.


Java Programming Language


Java was debuted in 1995 and was created at Sun Microsystems by James Gosling (which in 2009 was acquired by Oracle). It is a free, open-source, object-oriented programming language for general-purpose use. Java is a cross-platform programming language that runs on virtually any device, operating system, or server. Furthermore, because it is compiled to bytecode, it is compatible with any Java Virtual Machine (JVM).

Additionally, Java is statically typed, which means that type checking occurs at compile time. Indeed, Java’s syntax is similar to those of C and C++ but provides fewer low-level features.

Kotlin Programming Language

Kotlin is a significantly more recent language than Java, having been released in 2016. It is a free and open-source programming language that can also compile to bytecode and run on the Java Virtual Machine (JVM), allowing it to run on practically any platform. Additionally, Java libraries and frameworks are compatible with Kotlin projects.

Kotlin is a language inspired by Java that expresses an enhanced version of cleaner, simpler, and faster to compile. It combines object-oriented and functional programming.

Why a Comparison between Kotlin vs Java?

As previously said, Java is a general-purpose language that, together with JavaScript and Python, is one of the most popular in the world. While Kotlin is not currently vying for the top spot, it has proven to be a formidable contender in the Android development space.

Google recognized Kotlin language as their second official language for Android development one year after its inception, in 2017. Two years later, in 2019, Google designated Kotlin as the preferred programming language for Android applications. As a result, this programming language experienced phenomenal growth.

Kotlin vs Java: The Differences!

Now that we’ve established some backdrop, you may be wondering how the expansion of Kotlin affects Java. Is Kotlin going to take its place? The solution is not that straightforward. There are numerous divergent viewpoints on this subject. To fully comprehend both sides of the disputes, let us first examine Kotlin vs Java and contrasts between them.

The code

One of the most significant distinctions between Kotlin vs Java is that Kotlin requires significantly less code. It is a highly concise language, which decreases the likelihood of developers creating code errors and simplifies their work.


In general, Kotlin’s brevity makes huge projects more manageable, as it often requires fewer lines of code than Java to write the same methods. Additionally, it understands how to keep it brief and direct without jeopardizing the readability of the syntax.

Null Safety

The infamous NullPointerExceptions in Java are a source of considerable frustration for developers. NullPointerExceptions enable users to assign a null value to any variable. Suppose, however, that users attempt to utilize an object reference that contains a null value. NullPointerExceptions are thrown in this circumstance, and developers must handle the resulting exception.

In Kotlin, on the other hand, it is not possible by default to assign null values to variables or objects. If we attempt this, the code will fail to compile. As a result, Kotlin does not throw NullPointerExceptions. However, if the developer intentionally assigns a null value, the variable in issue can be marked as nullable. To accomplish so, a question mark must be added:
number of variables: Int? = null

Extension Functions

In contrast to Java, Kotlin enables developers to enhance the functionality of classes without necessarily inheriting from them. To conduct an extension function in Kotlin, the developer must prefix the name of the class (to be extended) with the name of the newly constructed function using the ‘.’ notation.

If you want to expand the functionality of an existing class in Java, you must build a new class and inherit the parent class’s functions. That is, the extension function is disabled.

Coroutines Support

By default, components of the same program operate in the same process and thread, referred to as the main thread, which is responsible for the user interface. Network I/O and procedures that need a lot of CPU power are deemed long. When either of these procedures is started, the thread that launched it is blocked until the operation is complete.

Java permits the development of several background threads to minimize problems on the main thread when performing lengthy processes. The disadvantage is that handling numerous threads is a complicated operation that may result in additional code mistakes.

Similarly, Kotlin supports the creation of numerous threads. Nonetheless, it proposes a more elegant and simple solution: coroutines. How are coroutines implemented? On the other hand, Coroutines are stackless and enable developers to create code, stop the execution, and then restart it. This enables the execution of non-blocking asynchronous code that seems to be synchronous. Thus, rather than creating several threads that the developer must manage afterward, coroutines prevent creating an excessive number of threads. Additionally, they are more readable and concise than Java’s solution.

Classification of Data

On the one hand, developers in Java must create fields (or variables) to store data, a function Object() { [native code] }, and getter and setter functions for the fields/variables, as well as other functions such as hashCode(), equals(), and function toString() { [native code] }() ().

To be honest, these classes are primarily used to store data and provide little (or extremely limited) functionality.

On the other hand, Kotlin simplifies creating data-holding classes by simply including the “data” keyword in the class declaration. The compiler will then automatically produce constructors, getter, and setter functions for multiple fields/variables.

Smart Casts

To cast an object in Java, the developer must verify that the variables’ types match the action.

In Kotlin, the smart casts feature handles casting checks. Through the “is-checks” keyword, Kotlin’s intelligent compiler manages superfluous casts (with stable values) automatically.


On Kotlin, checked exceptions are not available. As a result, developers of Kotlin are not required to catch or declare exceptions. Is this a positive development? To some extent, yes.

Java developers have verified that exception handling is supported. As a result, they must identify and declare exceptions. On the one hand, this can be a source of frustration and wasted time. On the other side, it guarantees that code is robust and that mistakes are handled appropriately. Thus, checked exceptions support has several advantages and disadvantages. Ultimately, it is determined by the developer’s top priorities.

Higher-Order Functions and Lambdas: Functional Programming

As noted at the outset, Kotlin is a cross between object-oriented and functional programming. Functional programming is a declarative method of programming that uses mathematical functions to do computations. High-order functions and lambda expressions are both ideas used in (some) functional programming. The first one implies that functions should be treated as first-class entities. As a result, Kotlin, a statically typed language, may use various function types to express functions. In other words, functions can be implemented in a variety of ways.

Additionally, lambda expressions and anonymous functions are supported in Kotlin. These are referred to as a “functional literal.” As a result, it represents an undefined function that immediately passes as an expression.

Java, on the other hand, is more constrained by the concept of object-oriented programming. However, it has made considerable progress toward functional programming as well. Since Java 8, which was released in 2014, Java has supported lambda expressions, which are functions that are not required to belong to a class. Indeed, lambda expressions in Java can be provided as objects and are available for execution on demand.

Additionally, with the addition of lambda expressions, Java began to enable higher-order functions. A function is associated with a method in Java, and Java 8 enabled lambda’s return from methods.

Primitive Types

Primitive type variables are not objects in Java; they are predefined Java data types. Java has eight primitive data types: int, byte, short, double, float, boolean, char, and long. As a result, these variables cannot be represented by an object derived from a struct or a class.

While primitive types are not classes, Java developers can wrap a primitive type’s value. To accomplish this with Java, the developer needs to specify it explicitly.

In comparison, once a variable of a primitive type is initialized in Kotlin, it is instantly deemed an object.

Public Fields

Java supports public fields (a.k.a. non-private fields). They can be rather useful when the callers of an object require modification to conform to the representation of that object, as they enable the developer to change the representation of an object without requiring the callers to be adjusted. Thus, the public API remains unmodified, and the software maintains a level of maintainability.

By contrast, Kotlin lacks public fields.

Types of Wildcards

Typically, a question mark (?) in code indicates an unknown type (type of variable, field, or parameter).

In Kotlin vs Java, Kotlin does not support wildcards. Rather than that, it has a declaration-site variance and type projections as a fallback.

Implicitly Conversions

On the one side, Kotlin lacks implicit widening conversion capability. As a result, smaller types cannot be transformed into larger ones.

To circumvent this, Kotlin developers must perform an explicit conversion.

In Kotlin vs Java, Java enables implicit conversions, which eliminates the need for developers to conduct explicit conversions.

Which one should you Choose, Kotlin vs Java?

To begin, both Kotlin vs Java, notwithstanding their differences, compile to bytecode. As a result, developers may simply convert Kotlin code to Java or vice versa, allowing both languages to be utilized concurrently in the same development project.

As previously stated, Kotlin does provide various advantages for Android development, but is it superior to Java? To be sure, it does have a few advantages over its competitor:

• Reduces the amount of code required
• Deployment is lightweight and compiles more quickly.
• Coroutines are supported
• It is compatible with the libraries and frameworks included with Java.
• There will be no more NullPointerExceptions.

Let us not forget, however, that Java also has some “moves up its sleeve”:

  • Robust coding
  • cross-platform compatibility with virtually any server
  • operating system, or device.

Android is a Java-based operating system.

It has a long history; as a result, it has a larger community and documentation, as well as a robust ecosystem with several libraries and tools.

Now that we’ve emphasized the advantages of each language, it’s even more difficult to select between Kotlin vs Java, isn’t it? Let us attempt a more practical examination. Kotlin has been gaining traction as the new Android programming language. Its success includes critical features that simplify developers’ lives, such as extension functions, lambda expressions, higher-order functions, coroutines, and no NullPointerExceptions.

These are only a few aspects that demonstrate why Kotlin is superior to Java for Android development and is expected to continue to do so in the future. Everything appears to be moving toward Kotlin, as seen by the emergence of new development tools! However, Java retains considerable importance and should not be overlooked.

Java retains its dominance in general-purpose programming. Even when developing for Android, it remains a fantastic language, and it’s quite apparent why some developers chose it. To be honest, it also relies on the development team’s language preferences and whatever programming language feels more natural. All of these are legitimate concerns. Additionally, Java has been one of the most popular programming languages for years, so the likelihood of it being completely replaced shortly is slim.


Kotlin appears to be the best option for Android development at the time. Numerous businesses and developers are adopting it, and the language is expected to continue to expand in popularity.

Java, on the other hand, continues to be a great general-purpose language. Android’s preferred browser has been for a lengthy period, indicating that it will not be rapidly displaced.

In conclusion, whether language is superior is not straightforward and is likely to generate lively debates. Additionally, other factors to consider and the language differences, such as the language used by businesses and the level of comfort developers have with Kotlin vs Java.

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