Clojure Vs. Java Comparison Guide in 2021

Not sure if learning Clojure is a good idea? Read on and discover the Clojure vs. java main advantages and disadvantages.

Updated on July 25, 2022
Clojure Vs. Java Comparison Guide in 2021

Developers can get picky when it comes to learning programming languages and using them for different purposes. The reason is that they want to use those with better performance, that way they can increase their productivity. In this article, you’ll see a Clojure and Java comparison guide.

When developers build and maintain web applications, most of them consider Java at the top of their list, as this language has been popular for many years. However, nowadays, another newer and simpler programming language is gaining more popularity as Clojure’s clock ticks. So, the question for many is which of these programming languages to use? We made a detailed Clojure Vs. Java comparison to help you understand both languages and their advantages and disadvantages.

Clojure Vs. Java Comparison Guide in 2021

Clojure vs. Java Comparison: Pros and Cons

Maybe you heard a coworker speaking about the wonders of Clojure, making you want to start implementing that programming language. But then you also heard someone on a forum talk about how Java will always rule the world. Confusion increases, and you might feel lost not knowing what to do, whether to stick with Java or to learn and use Clojure.

Before making any snap decision, learn what the main advantages and disadvantages of each programming language are. This way, you can make an objective decision based on the facts.

Let’s take an overview of both programming languages, with their pros and cons.


Clojure is a dynamic and functional dialect of the Lisp programming language on the Java platform.  This language made its first appearances in 2007 and its first stable release in 2009. It’s created by Rich Hickey, who wanted to make programs simpler than those that already existed. His main objective was to speed the software development process by making a language that was easy for developers to understand and implement.

13 years later after its release and some developers are claiming that Clojure is overthrowing Java. For these Clojure defenders, this programming language is better than Java for many reasons. For example, they state that with Clojure, they can write better and more flexible programs.

These are the pros and cons of using Clojure:

Clojure Pros

  1. Immutable Data Structures

One of Clojure’s biggest advantages is that because it has features of an object-oriented language, it includes immutable structures. This means that any operation that a developer makes won’t change its values. Instead of changing them, Clojure creates a new structure in the form of a tree that contains the new data added.

This immutability is useful when creating applications that contain many threads because instead of synchronizing and changing variables in each thread, it creates entirely new structures.

  1. Functional Approach: Clojure Vs. Java Comparison

One of the differences that Clojure has with other Lisps is regarding functional programming. Clojure encourages writing pure functions.  The result of such functions depends only on the input parameters. This means that it doesn’t matter when you start the function; the result will always be the same, benefiting developers by simplifying the testing process.

  1. Lisp Programming

As Clojure is based on the Lisp family of languages, it includes many Lisp features, such as homoiconicity. Lisp source code consists mostly of lists, so programs using this language can manipulate source code as a data structure. This creates a macro system that helps programmers to create a new syntax embedded in Lisp.

In simpler terms, a Clojure developer can access and transform code as data.

  1. Concurrency: Clojure Vs. Java Comparison

Most systems deal with many simultaneous tasks, and developers have to deal with multiple threads to deal with these systems. However, doing so can be difficult because of the complexities of synchronization.

Here’s when Clojure comes to save the day by simplifying multi-threaded programming in several ways.

According to ‘’Because the core data structures are immutable, they can be shared readily between threads. However, it is often necessary to have state change in a program. Clojure is a practical language that allows the state to change but provides a mechanism to ensure that it remains consistent when it does so.”

Clojure was created to make programming simpler, which includes writing concurrent programs simple and easy. This allows programmers to write code making a smaller number of errors, and as a result, programming is much more productive.

Clojure Cons

  1. Difficult to Learn

Clojure is praised for being a functional and simple language. However, it has one of the highest learning curves of any programming language. Not just because it has complicated rules, but because understanding how Clojure works and even understanding how to install the program can be difficult for some developers.

  1. It Depends on the Java Libraries

Because Clojure has interoperability with Java, there is a high dependency on the Java libraries rather than libraries written in Clojure. So, even though Clojure is a practical and functional language, most programs use Java libraries that tend to be less functional and have other side effects. This could affect your program’s performance, especially if you are regularly mixing java data structures with Clojure data structures.

  1. Parenthesis

This problem mostly affects programmers who are just starting to work with Clojure and have more of an outsider’s perspective.  However, Clojure it’s indeed full of parentheses that might seem problematic for most. But the good thing is that many tools help programmers with structural editing, and with time they get used to the brackets.

  1. Slow Startup Time

One of the most common complaints regarding Clojure is its long startup time. Compared with other languages (Python, Node, Ruby) with less than 100 millisecond startup time, Clojure’s seconds feel like an eternity. The reason behind this is that Clojure runs on the JVM. Not that JVM is a problem itself, but because JVM as a platform makes Clojure startup time even slower.


Java is a class-based, object-oriented programming language designed for having fewer implementation dependencies. It is also a general-purpose programming language that helps programmers write once, run anywhere (WORA). Java is known to be fast, secure, and reliable. This is why it’s widely used to develop applications, data centers, and cellphones, among other things.

James Gosling originally built Java in 1995 at Sun Microsystems that has now been acquired by Oracle. And after its release, it quickly became popular among the IT community.  And after 25 years of its release, it remains among the top 10 programming languages of many rankings.

These are the pros and cons of using Java:

Java Pros

  1. Is an Object-Oriented Programming Language

Instead of writing procedures or methods that perform data operations (procedural programming) with object-oriented programming (OOP), developers can create objects containing both data and methods. Programmers can declare classes, create objects, and interact between two objects.

OOPs, a concept also helps developers increase security by binding the data and functions into a single unit and helps them organize large modules into smaller ones, making them more understandable.

  1. Java is Secure: Clojure Vs. Java Comparison

Did you know that Java is the first programming language that includes security as part of the design? Java reduces security threats and risks by avoiding the use of explicit pointers. A pointer can cause unauthorized access to memory because it stores the memory address of another value. However, this problem in Java because it doesn’t have explicit pointers.

There’s also a security manager in Java for each application that defines the access rules for classes.

  1. Platform Independency

Java has the Write Once Run Anywhere (WORA) feature that, despite sounding like a marketing phrase, means that the Java code can literally run anywhere. It doesn’t matter if a machine has a different operating system; developers don’t need to install any special software for it to work. The only requirement is that JVM must be present in the machine.

  1. Rich APIs

Java offers developers APIs for application development. The Java API consists of a library of prewritten classes that are free to use. The library contains components for managing input, database programming, and more. It’s divided into packages and classes, which means that a developer can import a single class or an entire package from the library that contains all the classes that belong in the specified package.

Java Cons

  1. Memory space

One of Java’s major drawbacks is that it requires a significant amount of memory space.  This is mainly because, in Java, the memory is managed through a garbage collection. Whenever the garbage collector runs, it affects the performance of the application and its memory efficiency.

  1. Verbose and Complex Codes

Java code characterizes by being verbose and complex. This means that there are many words in it, and there are complex sentences that are difficult to understand. When comparing Java with other programming languages such as Python, it’s noticeable to see how Java overcomplicates to write a simple command. This makes developers have a drastically huge code that turns out to be more complicated than in other languages.

  1. Poor Performance

Java is memory-consuming, making it much slower than native languages, especially when compared to C or C++. Another reason that causes it to be slow and poor performance is that each code in Java has to be translated to the machine level code. Also, because the garbage collector consumes more CPU time.

  1. It’s Not Free

Java is essentially free. However, for companies, enterprises, or all those who want to use Java for commercial purposes they have to acquire a license. Oracle announced in January of 2019 that Java SE 8 public updates would no longer be available for businesses without a commercial license. However, it remains free for those with general-purpose computing usage. So, if you are a company needing to run updates or fix bugs, you’ll be charged by the users you have or for the processor.

Clojure Vs. Java: Which One to Choose?

You’ve read all the benefits and disadvantages both programming languages have, and you might still have the Clojure Vs. Java debate in your head.

So, what’s the best option? Clojure? Java?

The truth is that there’s no winner here because it depends mostly on your priorities and the aspects you consider your project/website/platform should have. Java is still more popular than Clojure, despite being 25 years old! However, Clojure has increased its popularity over time for being a simple and functional language.

Comparing both languages and deciding what to choose is up to you! Some are still many Java defenders, while others are switching sides and going all-in for Clojure. Which one are you?