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Basic differences between Kotlin & Java

Harsh Vardhan
Harsh Vardhan
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Before beginning with the differences between Kotlin and Java, let’s have their introduction;


Java is a high level, robust, object-oriented and secure programming language, owned by Oracle. It is also a development platform because it provides a comprehensive set of tools and frameworks including the Java programming language, the Java Virtual Machine (JVM), and various APIs (Application Programming Interfaces) that enable developers to create a wide range of applications. It is used to develop mobile apps, web apps, desktop apps, games and much more.


Kotlin is a high level programming language developed by JetBrains in 2010. Kotlin was developed primarily to address the shortcomings of the Java programming language and to provide a modern, efficient, and safe alternative to it. It has both object-oriented and functional constructs. It is cross-platform, statically-typed and makes the code more concise and expressive. Also it can run on J.V.M , which makes it interoperable with Java code.

Kotlin can be used for any kind of development, be it server-side, client-side web and Android. Also Google’s Android Team has announced it as an official language for Android Application Development.

Basic Differences between Kotlin and Java

1. Semicolon

In Java, the semicolon is a separator that is used to terminate a statement. That is, each individual statement must be ended with a semicolon.

In Kotlin, semicolons are optional, and therefore line breaks are significant.

2. Variable Declaration

In Java, we can declare and assign multiple variables in one line.

But in Kotlin, it is not possible in the same way.

Solutions :

i. Separating declarations by semicolons :

ii. Assigning two variables using a Pair object :

iii. Assigning multiple variables using an array or a list :

3. Characters

In Java, characters are represented using the char primitive type, which can also be used in some contexts as a numeric value, representing the Unicode code point of the character.


Whereas in Kotlin, characters are not numbers. They are distinct from numeric types such as integers and floats. Char type represents a single character in Unicode encoding and is denoted by the keyword Char.

Solution : But we can assign the code of character to a variable of integer type.

4. Keywords

In Java, Keywords are predefined words that cannot be used as an identifier.

In Kotlin, Keywords are classified into three types :

i. Hard Keywords : They are always interpreted as keywords and cannot be used as identifiers. Example : in, as, break, class, continue, do , etc.

ii. Soft Keywords : These keywords are the are treated as keywords only in certain context which means we can use them as identifier. Example : catch, constructor, delegate, finally, file, etc.

iii. Modifier Keywords : Following is the list of tokens which act as keywords in modifier lists of declarations and can be used as identifiers in other context. Example : abstract, actual, annotation, companion, etc.

Also some of the Kotlin keywords are valid identifiers in Java. Example : in, object, is, and so on. If a Java library uses a Kotlin keyword for a method, you can still call the method, escaping it with the back-tick (`) character. Here, in is a hard keyword in Kotlin.

5. Operators

In Java, Operator is just a symbol that performs operations.

In Kotlin, operators are actually treated as functions with a special syntax that allows them to be used in infix notation. This means that you can define your own operators by defining functions with special names, and then use them in infix notation like you would with built-in operators. Example :

6. Bit-wise operation

Java has symbols for bit-wise and bit-shift operations.

 But in Kotlin, there are no symbol for bit-wise and bit-shift operations.

Solution : The usual symbols ,like <<, >>, |, &, and ^, are missing, but we can do bit-wise and bit-shift operation with functions of classes Int and Long.

List of all those functions :

7. If

In Java, If is an statement that specifies a block of code to be executed, if a specified condition is true.

Whereas in Kotlin, if is an expression. An expression consists of variables, operators, methods calls etc that produce a single value. So, ‘if’ returns a value.

8. Ternary operator

In Java, the ternary operator is a type of Java conditional operator, which can be used in place of if-else conditions.

But in Kotlin, there is no ternary operator.

Solution : As if is an expression in Kotlin. So, ordinary if works fine in the role of ternary-operator.

9. Elvis Operator

The Elvis operator is a shorthand notation used in programming languages to simplify the process of null-checking while dealing with nullable variables. In Java, there is no elvis operator because Java does not have built-in support for nullable types, so null-checking is often done manually using if-else statements or other constructs.

Kotlin has elvis operator to be used in situations where we need to assign a default value to a variable if the original value is null.

10. “!!” operator

The !! is not a part of Java syntax.

It is a feature of the Kotlin programming language. In Kotlin, the !! operator is known as the “not-null assertion operator,” which tells the compiler that a variable is not null, even if it is not explicitly marked as such.

The “!!” operator tells the compiler that the result of readLine() will not be null, and throws a NullPointerException if the result is null.

11. Automatic Type casting

As we know Java supports implicit type conversion from smaller to larger data types. An integer value can be assigned to the long data type.

But, Kotlin does not support implicit type conversion. An integer value can not be assigned to the long data type.  Example :

Solution : The helper function can be used to explicitly convert one data type to another data type. Example :

12. Function names

 Kotlin has naming rules for functions that are very similar to Java’s naming rules for methods, with one key difference: in Kotlin, you can use backticks around a function name. Example :

13. Top level Functions

In Java, it is required to create a class to hold a function, they can not be declared at the top level. Top=level functions are especially useful for defining helper or utility functions. It does not necessarily make sense to group them with other functions or create them when the contained object that adds no value.

In Java, in place of that, we have static functions inside helper classes.

In Kotlin, we do have top-level functions.

14. Infix notation

 In Java, functions or methods are typically written using prefix notation, where the function name comes before the arguments. Example:

But Kotlin allows you to define infix notation for functions using the infix keyword. This allows you to write function calls in a more natural, operator-like syntax, with the function name appearing between the arguments. Example :


In conclusion, Kotlin and Java are both powerful programming languages, each with its own set of features and capabilities. Java has been a widely-used language for decades and continues to be a popular choice for various application types, including mobile, web, and desktop development. It offers a robust set of tools and frameworks, making it suitable for a wide range of projects.

On the other hand, Kotlin, developed by JetBrains, was created to address the limitations of Java and provide a more modern, efficient, and safe alternative. Kotlin’s interoperability with Java, thanks to its ability to run on the JVM, makes it an attractive option for developers looking to gradually migrate from Java to Kotlin or to leverage existing Java libraries.

While both languages have their strengths and weaknesses, the choice between Kotlin and Java ultimately depends on the specific requirements of the project, the development team’s preferences, and the existing ecosystem. With Kotlin’s growing popularity and the continuous evolution of both languages, developers have powerful tools at their disposal to build robust and innovative applications for various platforms.


The real author of the blog is Nadra Ibrahim you can find her blog here. Click me!

Harsh Vardhan

Harsh Vardhan

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