What Is an Applet?

An applet is a small application designed to perform a specific task within a larger program or website. Typically written in Java, applets can be embedded into web pages to provide interactive features such as games, calculators, or visualizations.

An applet is a compact, specialized application that is typically embedded within a larger program or web page to perform a specific function. Often written in Java, applets are designed to be executed by a web browser's Java Virtual Machine (JVM), allowing them to consistently run across different platforms. They are commonly used to add interactive features to web pages, such as simulations, visualizations, games, or calculators, without requiring users to install standalone software.

Applets operate within a restricted security environment, known as a sandbox, which limits their ability to access the local file system or network resources, thereby enhancing security. When a user accesses a web page containing an applet, the browser downloads the applet's code from the web server and executes it locally within the browser's context. This enables the applet to interact with the user in real time, offering a richer and more dynamic user experience compared to static HTML content.

Applet vs. App

An applet and an app both serve to perform specific tasks, but they differ significantly in their scope and execution environment.

An applet is a small program typically written in Java, designed to run within a web browser and provide interactive features on a web page. It operates in a controlled environment with limited access to system resources, ensuring security but also restricting functionality.

On the other hand, an app, short for application, is a standalone software program that runs directly on an operating system, be it on a computer, smartphone, or other devices. Apps have full access to system resources, allowing them to offer a broader range of functionalities and more complex operations.

While applets are embedded within web pages and executed by the browser's Java Virtual Machine, apps are independently installed and run on the user's device, providing a more robust and versatile user experience.

How Does an Applet Work?

An applet is embedded within a web page and executed by the user's web browser. Here's a step-by-step explanation of how an applet functions:

Embedding in HTML. The applet is embedded in an HTML document using the <applet> tag (though this is deprecated and replaced by the <object> or <embed> tags in modern HTML). The HTML page includes a reference to the applet's Java class file.
Downloading the applet. When a user accesses the web page containing the applet, the browser downloads the applet's Java bytecode from the web server.
Java Virtual Machine (JVM) execution. The browser's built-in or plug-in Java Virtual Machine loads the applet and begins execution. The JVM provides a runtime environment for the applet, ensuring it runs consistently across different platforms.
Initialization. The applet's lifecycle methods are called by the JVM in a specific order. First, the init() method is executed to perform any necessary initialization. This method is called only once when the applet is first loaded.
Starting the applet. After initialization, the start() method is called to start the applet's execution. This method is invoked each time the applet's HTML page is visited or revisited.
Running and interacting. The applet runs and interacts with the user through graphical components like buttons, text fields, and other elements provided by the Abstract Window Toolkit (AWT) or Swing. The applet can also perform animations, calculations, or other tasks.
Stopping the applet. When the user navigates away from the web page containing the applet, the stop() method is called. This method pauses the applet's execution and is invoked each time the user leaves the page.
Destroying the applet. Finally, when the browser closes, or the applet is no longer needed, the destroy() method is called to perform any necessary cleanup. This method is called only once, just before the applet is unloaded from memory.

What Are Applets Used For?

Applets are used for a variety of purposes, primarily to enhance the interactivity and functionality of web pages. Some common uses of applets include:

Interactive content. Applets provide interactive features such as games, simulations, or educational tools directly within a web page. They allow users to engage with dynamic content without leaving their browsers.
Data visualization. Applets can be used to create interactive charts, graphs, and other data visualization tools, enabling users to explore and analyze data in a more intuitive and engaging way.
Form validation. Applets can perform client-side validation of form data before it is submitted to the server. This functionality reduces server load and improves user experience by providing immediate feedback on data entry errors.
Multimedia. Applets can handle multimedia tasks such as playing audio and video files, displaying animations, or even providing simple image editing tools.
Calculators and tools. Applets are often used to create various online tools and calculators, such as financial calculators, scientific calculators, or unit converters, allowing users to perform complex calculations directly within the browser.
Online learning and training. In educational settings, applets are used to create interactive tutorials, quizzes, and other learning materials that help users understand complex concepts through hands-on interaction.
Real-time applications. Applets can be used in real-time applications, such as live monitoring systems for network traffic, stock market analysis, or weather updates, providing users with up-to-date information.
Enhanced user interface components. Applets can provide custom user interface components, such as interactive menus, draggable elements, or sophisticated form controls that are not easily achievable with standard HTML and JavaScript.

Applet Types

Applets come in various forms, each designed to serve specific purposes and functionalities within web applications. Here, we'll explore the main types of applets and their unique characteristics.

Standalone Applets

Standalone applets are Java programs that are designed to run independently of a web browser. They can be executed directly on a Java-enabled platform, typically through a command line interface or a standalone applet viewer. These applets are not embedded in web pages but can still provide interactive features and graphical user interfaces. Standalone applets are useful for testing and development purposes, as well as for applications that don’t require browser integration.

Embedded Applets

Embedded applets are designed to be embedded within HTML pages and executed by web browsers. These applets enhance web pages by adding dynamic content, such as animations, interactive forms, and real-time data visualizations. Embedded applets operate within the browser's security sandbox, which restricts their access to local system resources to ensure safe execution. This type of applet is commonly used to improve user experience by providing interactive features directly within web content.

Local Applets

Local applets are similar to embedded applets but are stored and executed from the user's local file system rather than being downloaded from a web server. These applets can be run within a browser or a standalone viewer and often have fewer security restrictions since they originate from the local machine. Local applets are useful for applications that require more extensive access to local system resources, such as file manipulation or integration with other local applications.

Remote Applets

Remote applets are hosted on a web server and downloaded to the user's browser when the web page is accessed. These applets deliver interactive and dynamic content over the internet without requiring the user to install additional software. Remote applets are commonly used for web-based applications, online games, and educational tools, where the applet's code is maintained and updated on the server, ensuring users always have the latest version.

Applet Examples

Applets have been used in a wide range of applications, each showcasing their capability to enhance web pages with interactive and dynamic content. Here are some examples of applets and their specific uses:

Online calculators. Applets are often used to create interactive online calculators, such as mortgage calculators, scientific calculators, or currency converters. These applets allow users to perform complex calculations directly within their browser, providing instant results without the need to refresh the page or rely on server-side processing. For instance, a mortgage calculator applet helps users estimate their monthly payments by inputting loan amount, interest rate, and loan term.
Educational simulations. Educational applets provide interactive simulations for learning complex concepts in subjects like physics, chemistry, and mathematics. For example, a physics simulation applet might allow students to explore the principles of projectile motion by adjusting variables such as angle, velocity, and gravity, and observing the resulting trajectory.
Interactive games. Applet-based games were popular in the early days of the internet, offering users a way to play simple games directly in their browser. Examples include classic arcade games, puzzles, and card games. These applets provided entertainment without requiring users to download or install additional software. Although modern web technologies have largely replaced applets for this purpose, they were an important stepping stone in the development of online gaming.
Data visualization tools. Applets can be used to create interactive data visualization tools, such as graphs, charts, and maps. For instance, a stock market applet might display real-time price movements of stocks, allowing users to visualize trends and make informed investment decisions. By enabling interactive features like zooming, panning, and hovering over data points for detailed information, these applets enhance the user's ability to analyze and interpret data.
Form validation applets. Form validation applets help improve the user experience by providing real-time feedback on form inputs. For example, an applet embedded in a registration form checks the validity of email addresses, passwords, and other user inputs as they are entered. This immediate feedback helps users correct errors before submitting the form, reducing server load, and improving the overall efficiency of data collection.
Multimedia players. Applet-based multimedia players were used to play audio and video files directly within the browser. These applets supported various media formats and offered controls for playback, volume, and navigation. An example is a streaming music player applet that allowed users to listen to audio files without leaving the web page. While modern HTML5 media elements have largely supplanted these applets, they were once a key method for delivering multimedia content online.