Applets have been a significant part of Java programming, primarily used for embedding applications in web browsers. However, many developers often wonder: on which side is an applet always executed? The simple answer is that Java applets always execute on the client side.
This topic explores how applets work, why they run on the client side, and their advantages and limitations. Understanding this concept is essential for anyone working with Java-based web applications.
1. Understanding Java Applets
What Is a Java Applet?
A Java applet is a small program written in Java that runs in a web browser. It is embedded in an HTML page and executed within the Java Virtual Machine (JVM) on the user’s computer. Unlike server-side applications, applets do not run on the server but are downloaded and executed by the client’s machine.
Types of Java Applications
To understand where an applet executes, let’s compare different Java applications:
- Standalone Applications: Run directly on a computer without needing a web browser.
- Servlets: Java programs that execute on the server side and handle client requests.
- Applets: Java programs that execute on the client side within a web browser.
Since applets run within the web browser, they do not execute on the server but rather on the user’s device.
2. Why Do Applets Always Execute on the Client Side?
The Role of Java Virtual Machine (JVM)
Every Java applet requires a Java Virtual Machine (JVM) to execute. When a user visits a web page containing an applet, the browser downloads the applet code and runs it using the JVM installed on the client machine. This process ensures that the execution happens locally rather than on the server.
Applets and the Client-Side Execution Process
- User Visits a Web Page: The web browser loads the HTML page that contains an embedded Java applet.
- Applet Code Is Downloaded: The applet class files are downloaded to the user’s system.
- JVM Executes the Applet: The client-side JVM interprets and runs the applet within the browser.
Because this execution happens on the user’s machine, applets are considered client-side programs rather than server-side applications.
3. Advantages of Client-Side Execution in Applets
Faster Performance
Since applets run on the client side, they do not require constant communication with the server. This reduces server load and improves performance. Once the applet is downloaded, it executes locally without delays.
Rich Graphical User Interface (GUI)
Java applets allow developers to create interactive graphical user interfaces (GUI) with buttons, text fields, and animations. Because the rendering happens on the client side, the application remains responsive and visually rich without server-side lag.
Security Features
Applets operate in a sandboxed environment, meaning they have restricted access to the user’s system. This ensures security by preventing malicious operations like modifying local files or accessing sensitive data.
Platform Independence
Since applets rely on JVM, they can run on any device that supports Java, making them cross-platform compatible.
4. Limitations of Java Applets
Despite their advantages, Java applets have several drawbacks that led to their decline in popularity.
Browser Compatibility Issues
Modern web browsers, such as Google Chrome, Mozilla Firefox, and Microsoft Edge, have stopped supporting Java applets. This has made them impractical for web-based applications.
Security Restrictions
While applets operate in a secure environment, web browsers often block Java content due to potential security vulnerabilities. Users need to manually enable Java, which reduces accessibility.
Dependency on JVM
For an applet to execute, the client’s machine must have Java Runtime Environment (JRE) installed. Many users do not have JRE, making applets less convenient.
Performance Overheads
Even though applets run on the client side, they require significant resources. Loading a Java applet can sometimes slow down a webpage, leading developers to prefer modern JavaScript-based solutions instead.
5. How Are Applets Embedded in Web Pages?
To execute an applet, it must be embedded within an HTML file. The traditional way to do this is by using the <applet> tag:
<applet code="MyApplet.class" width="300" height="200"></applet>However, modern browsers no longer support the <applet> tag. Instead, Java applets must be embedded using the Java Plug-in and the <object> or <embed> tag.
<object classid="java:MyApplet.class" width="300" height="200"><param name="code" value="MyApplet.class"></object>These tags allow the applet to be recognized and executed by the JVM on the client side.
6. Alternatives to Java Applets
Due to the decline of Java applets, developers now prefer alternative technologies that provide better security, compatibility, and performance.
JavaScript and HTML5
- JavaScript can handle most of the functionalities that applets once provided, including animations and form validations.
- HTML5 Canvas allows rendering of graphics without relying on external plugins.
WebAssembly (WASM)
WebAssembly enables high-performance applications to run directly in the browser, providing an alternative to applets with better execution speed.
Progressive Web Apps (PWAs)
PWAs use modern JavaScript frameworks to create cross-platform web applications that can run on any browser without additional plugins.
Java applets always execute on the client side because they rely on the JVM installed on the user’s machine rather than the server. While applets provided interactive and platform-independent applications, they have largely been replaced by modern technologies like JavaScript, WebAssembly, and HTML5.
Understanding the execution environment of Java applets is crucial for developers transitioning from older web technologies to modern solutions. As browsers continue to phase out support for applets, adapting to newer client-side frameworks is essential for web development success.