Applet facts for kids

In computing, an applet is a small computer program. It's designed to do one specific job. Applets run inside a bigger program or a special engine. Think of them like a small tool that helps a larger machine work better.

A common type was the Java applet. These were programs written in the Java language. They were often placed on web pages to add interactive features. Applets are usually quick and easy to use. They don't take over your whole computer screen.

What is an Applet?

An applet is different from a full-sized computer program. It's smaller and focuses on one task. For example, a calculator on a website could be an applet. It's not a full word processor, just a calculator.

History of Applets

The word applet was first used in 1990. It appeared in a magazine called PC Magazine. But the idea of small programs that download and run on your computer is even older. It goes back to 1969! Back then, a person named Jeff Rulifson described a way to download small programs. These programs helped people use a computer system called NLS over an early internet network. This idea was a lot like what Java applets would do later.

How Applets Work with Other Software

Applets often need a main program to run. They don't usually work by themselves. They might run inside a "container" provided by a host program. Or they might need a plugin for your web browser. Many mobile devices also use applet-like programs.

Web Applets

In the past, applets were very important for websites. They added cool interactive features that regular HTML couldn't do.

• They could react to your mouse clicks.
• They had controls like buttons and check boxes.
• Applets could change what you saw on the screen based on what you did.

This made applets great for showing things, like how physics works or how the human heart beats. Many websites had collections of applets for learning. Applets were also used to create online games. These games let players compete against each other in real-time.

An applet could also be just a text area. For example, it could let you type commands to a faraway computer system. Sometimes, an applet could even pop out of its dedicated area and run in its own window.

Web pages could also send special information to applets. This meant the same applet could look or act differently depending on the page it was on.

Here are some examples of web-based applets that were common:

• QuickTime movies
• Flash movies
• Windows Media Player applets, used for videos in web browsers.
• 3D modeling display applets, which let you spin and zoom 3D objects.
• Browser games that ran as applets.

Applets vs. Subroutines

You might wonder how an applet is different from a small piece of code called a "subroutine." A subroutine is just a small part of a bigger program. An applet is more like a mini-program itself.

• Applets usually run on your computer (the "client"). They add features that the main program or browser doesn't have by default.
• The main program or browser limits what applets can do. This is for safety.
• Applets are often written in a different, more powerful language than the web page's scripting language. This makes them faster or able to do more complex things.

Java Applets

A Java applet is a special type of Java program. It starts from an HTML web page and runs inside your web browser. It gets its code from a server and then runs on your computer.

Java applets could add interactive features to web applications. A great thing about Java code is that it can run on many different computer systems. This means Java applets could work on Windows, Unix, macOS, and Linux computers.

When your web browser loaded a page with a Java applet, the applet's code would be sent to your computer. Then, a special part of your browser (called the Java virtual machine) would run it.

Security for Applets

Making sure applets are safe is very important. This is true for applets on computers, phones, and other devices.

Web Applet Security

When you used a web browser with applets, there were ways to protect your computer from bad applets. A "malicious applet" is one that tries to harm your computer. It could try to stop your computer from working, steal your private information, or just annoy you.

A common way to protect against bad applets was for the web browser to watch what the applets were doing. This allowed the browser to stop any applets that were acting suspiciously.

See Also

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