12 Reasons Why Use Kotlin Over Java

Kotlin vs Java comparison. Top benefits of Kotlin over Java in Brights blog.

Back in the spring of 2019, Google announced Kotlin as the preferred language for Android development, and this, as expected, led to a new phase of confrontation between the two flagships of Android application development.

While Java is one of the most widely used programming languages in the world and is largely the traditional solution for Android development, there are many reasons why Java may not always be the best option for your Android projects. So, there are still disputes over the choice of language among developers.

On the one hand, everything is extremely simple: you need to write in the language that is convenient for you. However, on the other hand, one cannot deny the huge number of advantages and features that force developers to make a choice in favor of Kotlin.

Today we are talking about the key reasons why Java is inferior to Kotlin. Some of them you already know, and others you will discover for the first time.

So, what does Kotlin have that Java does not?


Kotlin offers much more simplified and short code compared to Java for the same tasks. By itself, this language is very easy to read and write, it is readable, simple to understand, and simple to debug.

Java programming is much more complex and Java code is longer. Java cannot be called a concise language, which means that there are many more potential mistakes when working with it. Kotlin, in turn, is a concise language, writing code in which is accompanied by a much lower probability of errors.

Java Compatibility

One of the key strengths of Kotlin is that this language interacts well with Java, it easily exchanges and uses information from Java in several ways. Java and Kotlin code can coexist within one project, and when working with Kotlin, you can use numerous libraries and Java frameworks, which means that the language is even more compatible.

Switching from Java to Kotlin is very easy — there is no need to convert the entire project to Kotlin, which means that programmers do not need to fully learn one more language. Anyone who knows Java can code in Kotlin.

Getting Rid of the Java Flaws

The traditional Java programming language has a fairly large number of shortcomings, and Kotlin solves them in many ways. This is possible due to the fact that Kotlin borrowed a lot from languages ​​such as C#, Scala, Pascal, and others.

Kotlin deletes boilerplate code and largely liquidates potential failures. Kotlin has delegations and late initializations, and just as importantly, it deals with safety issues in lists, which is not the case in Java.

Extension Features

Extension functions allow adding functionality to already defined types. In this case, types can be defined somewhere else, for example, in the standard library.

Kotlin provides the ability to extend a class by introducing additional functionality without the need to inherit from such a class and apply any patterns. This becomes possible thanks to special declarations that are extensions.

How does it work in practice? Developers can write features for a class from a third-party library they can’t make changes to. This is the extension function. Here, it is necessary to take into account that extension functions do not override functions that are already defined in the class. If an extension function has the same signature as an existing class function, then the compiler will simply ignore the extension function.


In Kotlin, all types are non-nullable by default. If you try to return or assign null, it will fail at compile time. However, by marking a variable as nullable, you can still assign a null value. This can be done by adding a question mark after the type.

In Java, when using a reference to an object with the specified null value, an exception appears in the form of “NullPointerExpertion!”. Which is missing in Kotlin.

Smart Casts

In Kotlin, the ‘is’ operator allows checking whether an expression belongs to a specific data type. This operator returns true if the value to the left of the operator is of the type specified to the right of the operator. If a local variable or property successfully passes the test for belonging to a certain type, then there is no need to additionally cast the value to this type. These transformations are called smart casts.

Such an operator can be applied both to base types, but to own classes and interfaces that are in the same inheritance hierarchy.

Built-in Higher-Order Functions

In Kotlin, you can speed up the execution of calculations using higher-order functions (which, unlike Java, are built-in). Each function in it is an object that captures the closure. Closures are variables that are accessed within the body of a function.

Memory allocations are required by both classes and functors, which naturally require a lot of execution time. To avoid such delays in Kotlin, you can insert lambda expressions directly into the code.

Lambda Expressions

Lambda expressions are a kind of specialized language construct. Together with anonymous functions, they are considered function literals, features that are capable of being passed as expressions, although they are not declared.

The last parameter of a function in Kotlin is a function, which is represented as a lambda expression that can be parenthesized. Also, Kotlin is able to independently determine the signature of the method, allowing you not to specify it.

Coroutines and Additional Threads

Kotlin provides the ability to create additional threads, but it also has so-called coroutines, which allow use of less memory compared to a regular thread because they are implemented without a stack.

Coroutines, in turn, are able to perform intensive and long-term tasks by suspending execution without blocking the thread and then resuming it. This further allows generating asynchronous code without blocking, which, when executed, cannot be distinguished from synchronous. In addition, they generate spectacular additional styles like async or await.

Java creates a background thread of the main intensive thread. But having multiple threads and managing them will not be easy and will lead to bugs in the code.

Easy Creation of Data Classes

In Java, all classes must be written manually by adding numerous lines of code, if we are talking about a large project. In Kotlin, it is possible to create special classes to define fields for storing data, a constructor, setter, and getter functions for each field, and toString, hashCode, equals functions. To do this, just add data to the class definition, then the compiler will do everything itself.

Kotlin also has specialized classes for representing arrays of primitive types without the packaging overhead: ByteArray, ShortArray, IntArray, and so on. These classes have no inheritance relation to the Array class, but share the same set of methods and properties. Each of them also has a corresponding factory function.

One or More Constructors

In addition to the primary constructor, Kotlin classes can have one or more secondary constructors, by adding them to class declarations. Java doesn’t implement this feature.

The main constructor is part of the class header and is declared immediately after the class name. Additional constructors are preceded by the keyword ‘constructor’. If a class has a primary constructor, each secondary constructor must directly or indirectly refer to the main one. This is done using the keyword ‘this’.


The delegation pattern is a great alternative to inheritance, and Kotlin supports it natively, freeing developers from having to write boilerplate code.

Delegation is a process that allows you to transfer your operations to another delegate. Kotlin, unlike Java, supports implicit delegation, also known as the alternative duplication method, which allows you to inject duplicate methods into your code. This eliminates the need to manually duplicate methods.

Android development is one of the key activities of Brights. Our developers apply advanced technologies and create applications based on the best world standards, cutting-edge practices, and using all the advantages of programming languages.

Trust us with Android development and experience all the strengths of Kotlin yourself.

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