Java vs. JavaScript: What is the Difference?

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What is Java?

Java is a general purpose programming language designed with one mantra in mind—”write once, run anywhere.” Java applications are compiled into bytecode that can run on implementations of the Java Virtual Machine (JVM). JVM helps bridge the gap between source code and the 1s and 0s that the computer understands. Any machine that has the JVM installed can run Java. In web development, Java features most prominently as a server-side language and the programming language of choice for mobile apps on the Android platform. It also still has a decent presence on the front-end as a Java applet, although this is falling out of favor due to security concerns.

Advantages of Java

As a general purpose programming language that has served as a backbone of many enterprise applications, Java advantages include:

• Widely used for enterprise, desktop, and Android apps. Java boasts a large active developer community and a mature development ecosystem with libraries, frameworks, and tools for every application.
• Short learning curve. Java’s long history and ubiquity, means there are plenty of tutorials, guides, and courses. If you encounter a problem, chances are high your question was already solved on StackOverflow.
• Cross-platform mobility. The JVM makes it possible to run Java apps on any device or operating system that has the JVM installed.
• Java Class Concurrency. Java’s built-in support for multithreading makes it easier to run tasks simultaneously maintaining parallel concurrency.
• Speed and performance. As a compiled language, Java is slower to start, but faster to run.  

Disadvantages of Java

Cons of using Java include:

• Security vulnerabilities. Because Java has been around a long time, the language’s inherent vulnerabilities are well understood by both security professionals and hackers alike. Java programmers must be vigilant about using the following security best practices such as keeping tools, libraries, and frameworks up to date.
• Memory hog. Java is notoriously known for its high memory requirements—the price you pay for thread-level concurrency is that each thread gets a certain amount of memory for its stack.

What is JavaScript?

Alongside HTML and CSS, JavaScript (standardized as ECMAScript) is considered one of the big three core components of the web. Employed by a majority of websites, JavaScript is a scripting language that typically runs in the browser and makes web pages dynamic and interactive. Today JavaScript is also quickly growing as a server-side technology since the release of Node.js in 2009.

Advantages of JavaScript

As the scripting language of choice for making websites interactive, JavaScript advantages include:

• Core technology of the web. Alongside HTML and CSS, JavaScript is one of the core technologies of the web and is responsible for making websites interactive. That means all the perks of an active developer community and development ecosystem complete with libraries, frameworks, and tools for web development.
• Easy to learn. JavaScript is one of the first languages many people learn, because of its simple syntax and ubiquity as a core technology of the web. That means there are plenty of courses, tutorials, and examples available on the web.
• Universal JavaScript apps. With the advent of Node.js it’s possible to create apps that use JavaScript across both the front end and back end of the technology stack. It’s possible to reuse code across web and mobile apps, cutting down on development time.

Disadvantages of JavaScript

Cons of using JavaScript include:

• Single threaded. The JavaScript event loop runs on a single thread. While fine for most web applications which run within browsers, the language lacks built-in support for concurrency and multithreading.
• Single point of failure. Because JavaScript runs on a single event loop, a single bug can halt all JavaScript code on a web page.

Java vs. JavaScript: Major similarities

As different as they are, there are some top level similarities worth considering, especially if you are looking at web development when comparing Java to JavaScript.

• Object-Oriented Programming (OOP). Both languages require the developer to code in terms of objects and their relationships to one another. By extension this gives both languages access to techniques like inheritance, encapsulation, and polymorphism.
• Front-End Development. Both languages can be used in aspects of front-end development. JavaScript can be embedded directly into HTML, implemented as a framework or library; Java can be used as a Java applet.
• Back-End Development. Both languages can be used on the server-side. Java has long been used to power back-end technologies like Apache, JBoss, and WebSphere. Node.js has become a launch pad for JavaScript-powered servers.

Java vs. JavaScript: Major differences

It’s important to remember that Java and JavaScript were developed to serve entirely different purposes. Java was designed as a general purpose programming language for building standalone applications, whereas JavaScript is a scripting language built specifically to interface with web technologies, namely HTML.

When Java was released by Sun in 1991, it was initially being used to program consumer electronics like VCRs. JavaScript was introduced to be used with Java as a client-side scripting language that could run in the browser without having to be compiled. Let’s take a closer look at some of the major differences between these two languages.

• Compiled vs. Interpreted. Java is considered a compiled programming language. JavaScript is considered an interpreted scripting language. The difference is in the implementation: Java is compiled into bytecode and runs on a virtual machine, whereas JavaScript can be interpreted directly by a browser in the syntax it is written (although it is usually minified in practice). With the advent of JIT compiling, JavaScript can also be compiled into optimized bytecode.
• Static vs Dynamic Type Checking. Java uses static type checking, where the type of a variable is checked at compile-time. The programmer must specify the type (integer, double, string, etc.) of any variable they create. JavaScript, like most scripting languages, uses dynamic typing, where type safety is verified at runtime. It is not required for a programmer to specify the type of any variable they create. There are many pros and cons for these two paradigms, but the primary advantage of static type checking is that type errors are caught early in development, and because the compiler knows exactly what data types are being used, code typically executes faster or uses less memory. The primary advantage of dynamic type checking is programmer productivity—you are free to assign types at your leisure.
• Concurrency. The ability to handle the execution of several instruction sequences at the same time is handled very differently between Java and JavaScript. Java makes use of multiple threads to perform tasks in parallel. JavaScript, particularly as it exists as Node.js in server-side applications, handles concurrency on one main thread of execution via a queue system called the event loop, and a forking system called Node Clustering. For most use-cases, both methods work just fine, but Java is generally faster because thread to thread memory sharing is much faster than interprocess communication (IPC).
• Class Based vs Prototype Based. Java follows class based inheritance—a top down, hierarchical, class-based relationship whereby properties are defined in a class and inherited by an instance of that class (one of its members). In JavaScript, inheritance is prototypal—all objects can inherit directly from other objects. Hierarchy is accomplished in JavaScript by assigning an object as a prototype with a constructor function.

Java vs. JavaScript: Security

Java and JavaScript have been around for a long time, giving hackers and security experts alike plenty of opportunities to understand where each language’s vulnerabilities lie.  ‍

Java security vulnerabilities and best practices

Common Java security vulnerabilities include:

• SQL injection is a vulnerability that occurs when a web application fails to sanitize user input into forms and other UI components. The attacker can submit a SQL query to execute SQL commands on the back end of your web app. To prevent SQL injection, it’s important to sanitize user inputs within your application and avoid using dynamic database queries altogether by sticking to prepared statements or parameterized queries.
• XML external entities (XEE) are a known vulnerability of Java libraries that parse XML. When a weakly configured XML parser processes malicious XML input containing a reference to an external entity, the attacker is able to modify that external entity to point to any location on the host machine (e.g., stored user data). It’s a common attack vector for denial of service attacks, server-side request forgeries, and port scanners. The best way to prevent XEE injection is to manually limit the capabilities of your XML parsers by disabling DTD processing. In cases where some DTD processing is required, proper configuration, encryption, and constant code scanning, can protect you against XEE.

JavaScript security

Common JavaScript security vulnerabilities include:

• Cross-site scripting (XSS) attacks. Websites or web apps that fail to implement a same origin policy are vulnerable to an XSS attack in which the attacker hijacks the webpage to deliver malicious code to visitors. The key to preventing XSS attacks is to filter input on arrival where user input is received, encode data on output, and using appropriate response headers to ensure browsers interpret your data correctly. Finally a content security policy (CSP) can monitor, detect, and stop XSS attacks when they occur.
• Code injection involves injecting JavaScript or Node.js code into web forms and other page features. Since JavaScript is an interpreted scripting language it’s easy for a hacker to manipulate and hijack a web page with code dynamically generated from the interpreter. Input sanitization best practices, such as whitelisting allowable characters while disallowing all others, can go a long way towards preventing injection attacks.
  

Java vs. Javascript: Speed and performance

Speed and performance comparisons between languages as different as Java and JavaScript are fundamentally flawed because of the different contexts in which the languages evolved. Furthermore, factors like programmer productivity and development ecosystem play much larger roles when choosing between languages.  

That said, there is increasing overlap between Java and JavaScript on the server-side of web applications making the comparison more valid than it was in the past. So how does server-side JavaScript (Node.js) stack up to Java?

Java speed

As a compiled language, Java is naturally faster than JavaScript when run on a virtual machine. Even when JavaScript closed that gap with JIT compilation, there is still the matter of Java’s built-in support for multithreading and concurrency. The ability to run processes in parallel across multiple threads is not to be underestimated. You can unlock the full potential of all the CPU cores on the host machine. The tradeoff is that managing shared memory across threads is not easy. A Java developer really has to know what they’re doing to manage concurrency at scale. In other words, while you can write real-time blazingly fast Java applications, in-practice it’s really hard to do right.

JavaScript speed

JavaScript reaps the benefits of both interpreted (quick start-up) and compiled (better performance over time) languages thanks to JIT compilation. JavaScript programs run interpreted initially but monitor and store the code for JIT compilation in the future. Node.js handles concurrency very differently from Java, opting to have a single main thread of execution with supporting background threads for performing  I/O work. An automated queue manages coordination between the main thread and these background threads. The end result is fast server-side JavaScript with an easier to reason-about concurrency model. For parallelism, Node.js relies on Node clustering, where child processes are forked to handle tasks in parallel. Parent and child processes communicate via IPC (interprocess communication). IPC is the main bottleneck for speed between JavaScript and compiled languages that have multithreading capabilities. That said for most general purpose applications, JavaScript’s unique combination of interpreted and compiled performance makes it a close race in terms of speed for general application design.

Should I use JavaScript or Java for my next project?

As with all languages, the choice really boils down to what you’re trying to build and what resources you have at your disposal. JavaScript is still very much a web technology, whereas Java is a general purpose language that can build anything.

You should consider Java if your project involves…

• Android Apps
• Enterprise Software
• Scientific Computing
• Big Data Analytics
• General Purpose Programming of Hardware
• Server-Side Technologies like Apache, JBoss, Geronimo, GlassFish, etc.

You should consider JavaScript if your project involves…

• Dynamic single page applications (SPAs)
• Front-End technologies like jQuery, AngularJS, Backbone.js, Ember.js, ReactJS etc.
• Server-Side technologies like Node.js, MongoDB, Express.js, etc.
• Mobile App Development through PhoneGap, React Native, etc.

Keep in mind that neither list is extensive, these are only meant as a starting point to help you get a feel for what you can expect and what keywords you can use to assess the best language for your needs.