Java and JavaScript

Java and JavaScript are two distinct programming languages that are often confused because of their similar names, but they were created for different purposes and work in different ways. Java is a general-purpose, object-oriented language designed so that compiled programs can run on many kinds of computer without change. Its slogan of writing once and running anywhere reflects this goal. JavaScript is a scripting language created to make web pages interactive, and despite the shared name it is a separate technology with its own history.

Java source code is compiled into an intermediate form called bytecode, which is executed by the Java Virtual Machine. Because a virtual machine exists for each platform, the same compiled program can run on different operating systems. Java is used for a broad range of software, from server applications to desktop programs. In the era of this site, small Java programs called applets could be embedded in web pages and run inside the browser, a use that has since faded as browsers withdrew support for them.

JavaScript runs inside the web browser and manipulates the page itself: it can respond to user actions, change the content and styling of the document, validate forms, and update parts of a page without reloading. Combined with HTML and CSS, it is one of the core technologies of web design, often described as dynamic HTML when used to alter the page on the fly. Other web technologies of the period, such as CGI scripts and Perl on the server, complemented these client-side scripts.

Frequently asked questions

Are Java and JavaScript the same?

No. They are separate languages with different designs and uses; the similar names are largely historical, and the two are not directly related in how they work.

What is the Java Virtual Machine?

The Java Virtual Machine runs the bytecode that Java source code is compiled into, and because a version exists for each platform, the same program can run on different systems.

What is a Java applet?

An applet is a small Java program that could be embedded in a web page and run inside the browser, a use that was common in earlier years but is no longer supported by modern browsers.