Java vs. JavaScript: What’s the Difference?

Java vs JavaScript—what’s the difference? Ask around and you’ll quickly pick up on the fact that there are few questions that more quickly conjure a web developer’s ire. After all, as famed web developer Jeremy Keith once poignantly put it—”Java is to JavaScript as ham is to hamster.” But for the uninitiated, you’d be forgiven for thinking there was some sort of link—both languages make a prominent appearance in the world of web development.As it turns out, JavaScript was originally called Mocha upon its conception at Netscape in May 1995, briefly changed its name to LiveScript in September, before finally receiving its current namesake in December that same year upon receiving a license from Sun Microsystems, the creator of Java. It would not be too much of a stretch to speculate that JavaScript was chosen as a marketing move, given the popularity of Java at the time.

Today however, the two languages have evolved to fill very different roles in web development and programming as a whole. Let’s take a closer look at the similarities and differences between Java and JavaScript.

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.

• 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 byte-code and run on a virtual machine, whereas JavaScript can be interpreted directly by a browser in the syntax it is written.
• 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.
• 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 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.