Question

How is an applet that is associated with a Web page executed on a user's system?

Short answer

Question: Explain the process of how an applet associated with a webpage is executed on a user's system. Answer: The process of executing an applet associated with a webpage on a user's system involves several steps. First, the user accesses the webpage containing the applet, and the browser identifies the applet code. Then, the browser interacts with the Java Runtime Environment (JRE) to execute the applet on the user's computer. The webpage must include an applet tag or an object/embed tag to specify the applet class file and any parameters needed. The JRE downloads the applet's class files, initializes the applet by calling its "init()" method, and the applet starts running. The user can interact with the applet, which may update the display or communicate with the web server. Finally, when the user leaves the webpage, the applet's "stop()" method is called, and the applet is unloaded from the browser.

Step-by-step solution

Accessing the Web page with an applet

When a user accesses a web page containing an applet, the user's web browser (such as Google Chrome, Mozilla Firefox, or Microsoft Edge) will load the page as usual, but it will also notice the presence of the applet code.

Java Runtime Environment

To execute an applet, the user's system must have the Java Runtime Environment (JRE) installed. The web browser will interact with the JRE to execute the applet on the user's computer. The JRE includes a Java Virtual Machine (JVM) that interprets and runs Java code.

Applet tag or object/embed tag

The web page containing the applet must include either an \ tag (deprecated as of HTML 4.01) or an

Applet class loading and initialization

The JRE will then download the applet's class file(s) from the web server to the user's computer. After downloading, the JVM initializes the applet by calling its "init()" method, allowing the applet to start running.

Applet execution and user interaction

Once the applet is initialized, it runs in the user's browser, typically providing some functionality or interactivity to the user. Users can interact with the applet (e.g., click buttons or input data), and the applet may dynamically update the display or communicate with the web server during its execution.

Applet termination

When the user leaves the web page containing the applet, the applet's "stop()" method is called, and the applet is unloaded from the user's browser. This ends the applet's execution on the user's system. In summary, an applet associated with a Web page is executed on a user's system through a series of steps that involve the web browser, Java Runtime Environment, and applet code. The applet is initialized, executed, and terminated as the user navigates the web page containing the applet.

Key concepts

Java Runtime Environment

The Java Runtime Environment (JRE) is essential for executing any Java program, including applets. The JRE acts as a kind of translator between the Java code and your computer's hardware. It understands Java language and converts it into a language your operating system can execute. At its core, the JRE includes three components:

• Libraries: Pre-written code to help execute common tasks
• The Java Virtual Machine (JVM): The powerhouse that interprets Java bytecode
• Class files and resources: Files that contain pre-compiled Java code

Every time you want to run a Java applet on your system, the JRE ensures that your computer is ready to handle the task. If the JRE is not installed, the applet cannot run. Therefore, it's crucial for users to have the JRE installed to fully interact with Java-based applications.

Java Virtual Machine

The Java Virtual Machine (JVM) is a key player in making sure that Java applications run smoothly. When a Java program is compiled, it's turned into bytecode, which is a set of instructions readable by the JVM. Here's how the JVM works:

• It receives the Java bytecode
• Converts the bytecode into machine code
• Executes the code on your machine

The beauty of the JVM is that it allows Java programs to be platform-independent. This means that a Java applet can run on any device that has a suitable JVM installed, regardless of the underlying hardware architecture. JVM helps in managing system resources and handles execution processes, memory allocation, and garbage collection, ensuring efficient execution of applets.

HTML applet tag

The HTML applet tag used to be the common way to embed a Java applet into a web page. Even though it's now deprecated, understanding its role helps grasp how applets were traditionally used:

• The tag signaled the presence of an applet on the page
• It included attributes like 'code', which specified the applet's class file, and 'width'/'height', which defined the display size
• The applet tag could pass parameters to applets for customization

While the applet tag provided a straightforward way to incorporate Java applets into websites, the move towards modern web standards has introduced alternative methods, like the

Web browser interaction

Web browsers serve as the conduit through which users access and interact with web-based content, including Java applets. When a browser encounters a page with an applet:

• It prepares to execute associated Java code by consulting the tags embedded in the HTML
• It relies on the JRE to load and start the execution of applets
• Interactivity is facilitated by allowing users to input data or perform actions within the applet

Modern browsers are designed to work with various web technologies and often run additional security checks before executing Java applets. This ensures a safe environment, as applets execute code on the user's machine. Efficient interaction between the browser, the JRE, and applets is crucial to providing a seamless user experience.