An Applet is a type of software that is designed to execute within the context of a larger program, often a web browser, providing rich, interactive features that the core program itself does not offer. Written in the Java programming language, applets are primarily used in network computing. They can respond to user inputs, such as mouse clicks or keystrokes, and they can also interact with other applets on the same webpage.
Historical Background of Applet
The history of applets dates back to the mid-1990s, when the Java programming language was first developed by Sun Microsystems. The term “applet” was first used in 1995, when Java was introduced to the world as a new programming language designed for the internet. The concept was to provide a small application (thus the term “applet”) that could be embedded within an HTML page and run within a web browser.
Expanding on Applets
Applets, as aforementioned, are small Java programs that can be integrated into an HTML page, run on the client side, and are executed by a Java Virtual Machine (JVM). An applet can run in any web browser that supports the JVM. They are used to make web pages more dynamic and entertaining. For example, they can display interactive graphics, or perform calculations based on user input.
An applet has a life cycle controlled by the browser and the JVM. The life cycle includes four stages: initialization, starting, stopping, and destruction. An applet begins its life when it is loaded and instantiated by the JVM. It is then initialized, started, and displayed on the web page. When the user navigates away from the page, the applet is stopped and then destroyed by the JVM.
The Inner Workings of an Applet
An applet consists of Java bytecode, which is a platform-independent representation of the program, and it runs inside a JVM installed in the browser. When a web page containing an applet is loaded, the browser’s Java plug-in downloads the applet’s bytecode, starts a JVM, and then loads and executes the applet within the JVM.
The applet interacts with the web page through the Document Object Model (DOM) and can also communicate with the server from which it was loaded, via HTTP or other internet protocols. However, for security reasons, it is typically sandboxed and restricted from accessing local files or certain system resources.
Key Features of Applet
- Platform Independence: Applets are written in Java, which is platform-independent. They can run on any device that has a browser supporting the JVM.
- Network Connectivity: Applets can communicate over the network, enabling them to be part of networked applications.
- Sandboxed Security: They operate within a security sandbox to prevent unauthorized access to system resources, thus ensuring user security.
- Rich User Interface: Applets can create complex graphical user interfaces (GUIs) and produce smooth animations, making them suitable for creating interactive applications.
Types of Applets
There are primarily two types of applets:
-
Local Applets: These applets do not need to connect to the internet after being downloaded. They run within the user’s browser and perform functions without needing to connect to a server.
-
Remote Applets: These applets require constant internet connectivity. They communicate with a server to perform their functions.
Usage of Applet and Associated Problems
Applets are commonly used to provide interactive features on web pages, such as games, calculators, animations, and interactive maps. They can also be used for more complex tasks like online voting, e-commerce, and remote desktop applications.
However, the use of applets has declined over the years due to several problems:
- Security Issues: Despite running in a sandbox, applets have been used in the past for malicious purposes, making many users and organizations wary of them.
- Performance: As applets run on the client-side, they can be slow to load and can consume significant system resources.
- Dependence on Java: Users must have a Java Runtime Environment (JRE) installed and properly configured in their browsers, which can be a complex task for non-technical users.
Comparison of Applet with Similar Terms
Here is a comparison of applets with similar concepts:
| Term | Definition | Execution |
|---|---|---|
| Applet | A small application embedded within an HTML page, run by a JVM in a web browser | Client-side |
| Servlet | A Java program that runs on a server, typically used to generate dynamic web content | Server-side |
| JavaScript | A scripting language for web pages, run by the browser’s JavaScript engine | Client-side |
Future Perspectives and Technologies Related to Applet
The future of applets is uncertain due to the rise of modern web technologies such as HTML5, CSS3, and JavaScript, which provide similar functionality without requiring users to install a JVM or deal with Java’s security issues.
However, there are still areas where applets have the upper hand, such as complex applications that require the full power of Java. Moreover, the Java Web Start technology allows launching full-featured Java applications directly from the web browser, which may bring a resurgence of applet-like functionality.
Applets and Proxy Servers
While applets and proxy servers are distinct technologies, they can interact in certain situations. A proxy server can mediate the connection between an applet and the server it communicates with, providing benefits like caching, filtering, and enhanced security. However, it’s important to note that the applet must be designed to support proxy servers and the user’s browser must be configured to use the proxy server.
Related Links
For more information about Applets, consider these resources:
