Applet facts for kids

In computing, an applet is a small computer program that does one specific job. It runs inside a larger program or a special engine, often like a plug-in. The word "applet" is often used for a Java applet, which is a program written in the Java language. These were designed to run directly on a web page. Applets are usually small and easy to use. They don't take up all your computer's attention.

What is an Applet?

An applet is like a mini-program that needs a bigger program to run. Think of it as a small tool that works inside a larger toolbox. For example, a web browser can be the "toolbox," and an applet could be a small game or a calculator that runs right inside the browser window.

History of Applets

The word applet was first used in 1990 in a magazine called PC Magazine. But the idea of small programs that you could download and run has been around even longer. Back in 1969, there was a description of a "Decode-Encode Language." This language allowed people to download small programs to help them use a computer system called NLS over an early internet network called ARPANET. This was a very early idea similar to what applets later became.

Applets as Part of Other Software

Sometimes, an applet can't run by itself. It needs a "host" program to provide a place for it to work. This could be through a plugin or other applications, including those on mobile devices.

Web-Based Applets

Applets were very useful for making websites more interactive. Before applets, web pages were mostly just text and pictures. Applets allowed websites to have things like:

• Interactive games you could play right in your browser.
• Tools for showing demonstrations or visualizations, like how a heart works or how physics concepts apply.
• Buttons and checkboxes that responded when you clicked them.
• Areas where you could type commands to a remote system.

Applets could also play videos or music formats that web browsers didn't support on their own. Web pages could even send special instructions to an applet. This meant the same applet could look or act differently depending on the page it was on.

Some examples of web-based applets included:

• QuickTime movies and Flash movies that played videos or animations.
• Windows Media Player applets for showing embedded video files.
• Programs that let you rotate and zoom in on 3D models.
• Many Browser games that you could play online without installing anything.

Java Applets

A Java applet is a special type of applet written in the Java programming language. These applets were launched from HTML web pages and ran inside a web browser. One of the best things about Java applets was that they could run on many different types of computers. This included Windows, Unix, macOS, and Linux systems. This is because Java code is "platform-independent."

When you visited a web page with a Java applet, the applet's code would be sent to your computer. Then, a special program inside your browser called a "Java virtual machine" would run it.

Applet Security

Because applets run on your computer, it's important to make sure they are safe. Over time, people became more aware of the security needed for these small programs.

Java Applet Security

Java applets had different ways to handle security. Some were "unsigned," meaning they had limited access to your computer. Others were "signed," which meant they came from a trusted source and could do more.

Web-Based Applet Security

For applets running in a web browser, many methods were used to keep them secure. A "malicious applet" is one that tries to harm your computer. This could include trying to stop your computer from working, stealing your private information, or just being annoying. A common solution was for the web browser to watch what applets were doing. This allowed the browser to stop any applets that seemed harmful.

See also

In Spanish: Applet para niños

• Application posture
• Bookmarklet
• Java applet
• Widget engine
• Abstract Window Toolkit