Applet In Java: Fundamentals You Need To Know

Download ebook

An applet is a Java application incorporated into a webpage. Even though it functions as a front-end, it runs within the web computer. As they operate inside the web browser, they make the page interactive and dynamic. Thus, Applet in Java is not a stand-alone program. Also, they are small applications that run within the address bar.

Difference Between An Applet and a Standalone Java

A few differences between an applet and a standalone Java application are as follows: 

1. Class Structure: Applet is a Java class that extends java.applet.Applet class.
2. Invocation: Java uses the main() method, but Applet invokes the start(). 
3. Embedding: Java is a standalone program, while HTML page embeds an applet.
4. Code Download: After you open an HTML page, you download the code for the applet. But in Java, you must download the entire code before compiling.
5. JVM Requirement: An applet relies on a web browser. On the other hand, Java executes without them.
6. Security Rules: The applet enforces strict security rules, often called sandbox security. Java is not subject to the same level of browser-enforced security.
7. Class Distribution:  Applets can download additional classes on runtime. But we must ensure all the necessary classes are available before running in Java.

How does Applet in Java work?

Applets uses the <applet> tag to load into a web page. The browser then downloads the applet’s code and runs it within the JVM. They run within a sandboxed environment for security reasons. Thus restricting their access to the user’s system. 

The Life Cycle Of An Applet

An Applet’s life cycle involves developing, launching, halting, and demolishing an object in an application’s implementation. In short, it has five main methods: paint(), destroy(), stop(), init(), and start(). Firstly, when an applet starts, it calls the following methods in sequence: init( ), start( ) and paint( ). When we destroy an applet, it calls the following methods in sequence: stop( ) and destroy( ). 

1. Init()

When we call the applet in the browser, it executes the init() function. Thus, the initializing phase happens. In the entire process, it calls the function only once. The web browser creates the initialized objects. Then, it executes the init() function inside the applet once it confirms the authentication setting.

2. Start()

The start( ) method executes after init( ). Moreover, this function is invoked in order to restart an applet after it stops. The init() is called only when the applet is loaded, but start( ) is accessed each time the HTML document is visible on the screen. So, if a user leaves a web page and returns, the applet resumes execution at the start() method.

3. Stop()

The stop() function ends the execution of an applet. Every time we minimize, pause, or switch between tabs, the applet triggers the stop() function. It calls the start() function again when we return to the same page.

4. Destroy()

When the applet completes its task, the destroy() function terminates it. For instance, when the applet in the tab or window is closed, the destroy() function is triggered. An applet, once deleted, cannot be restarted. Also, the stop() function is always invoked before the destroy() method.  

5. Paint()

The Graphics class contains the paint() function. It draws forms like squares, circles, trapeziums, etc in an applet. It executes this function after a call to the start() function. Also, the applet calls the paint( ) method each time it has to redraw an output. This situation can occur for several reasons. For instance, when we minimize and then restore the applet window. Again, we invoke the paint() method and the start() every time the applet in Java loads on the HTML page. 

Types of Applets

Depending on their storage place and ease of access, applets are classified as local or remote.

1. Local Applet

A local applet is created and stored on the local machine. When an HTML page recognizes a local applet in the Java system’s memory, it gets data from the pathname or folder name. Thus, a local applet defines two properties – the source folder that defines the path name and the code itself that defines the filename containing the applet’s programming. Top 10 Java Tools That You Should LearnTop 10 Java Tools That You Should Learn

2. Remote Applet

The remote applet is stored or is accessed remotely over the internet. To use the remote applet, we must have internet access on the system where the applet is accessible. Hence, we must be familiar with the remote applet’s Uniform Resource Locator (URL) or web location to find and download it.

Features of Applet in Java over HTML

• Displaying dynamic web pages of a web application.
• Playing sound files.
• Displaying documents
• Playing animations

Advantages Of Java Applets

Here are some of the advantages of Java Applets:

1. Interaction With Browsers

As applets are integrated into the web page, it helps the viewers to interact with dynamic information without leaving the page. This results in improved customer service while eliminating the need to obtain and set up separate programs.

2. Diminished Server Traffic

Since the applets are executed locally, it reduces the server’s workload. It also helps the users get more information. 

3. Availability

Applets can adapt to the changing frequency bands and computational power. Thus, they can load quickly for users with limited interactions and provide more capability for users with greater skills.

Disadvantages Of Java Applets

Here are some of the disadvantages of Java Applets:

1. Utilizing Excessive Performance And Resources

One of the major disadvantages of Applet in Java is its resource usage. It can sometimes cause crashes, hinder browser performance, and use the system batteries. As we know, slow performance and resource wastage is unacceptable. 

2. Insufficient Development Support

Many browsers discontinued to support applets. This is because of the comparison of applet programming with contemporary website creation tools. Thus, it becomes less appealing and more difficult to use applets.  This is because of the decreased availability of programming frameworks, libraries, and debugging resources.

3. Security Flaws

The application executes within the user’s browser and, thus, provides more access resources than web pages. As a result, it comes with a big cost: the possibility of security lapses. Fraudulent applets exploit these vulnerabilities to access private data, download malware, or interfere with system functions.

How Do You Run An Applet Through An HTML File?

Security flaws render Java applets obsolete despite their widespread use on the web. Also, the browsers do not support them. Thus making them a hazardous and obsolete technology. 

Let’s look at how we can run an applet in HTML: 

• We have to install the Java Running Environment. Compile your Java code. Include them in your HTML code file.
• The parameters, required resources, and the class name must be updated in the HTML using the <applet> tag.
• Open the HTML file using a browser that is compatible with applets.

How Do You Run An Applet Using The Appletviewer Tool?

Applets are still used with the help of the applet viewer application. It is used as follows:

• Compile Java and locate the class file.
• Using a command line, browse to the place where the class is found and type applet viewer in the prompt. A window pops up with the application running.

Conclusion

In short, the applet in Java is an important part of web development. With the introduction to applets, we could add dynamic and lightweight elements to web pages. They allowed us to add interactive and eye-catching features to the browser. But with the advancement of web technologies, security was a part of the concerns. Thus, applets lost their luster in contemporary Java programming. 

Recommended Reads

1. Top 20 Java Books for 2024
2. Applets

Explore Tailored Learning Paths

Enroll in Henry Harvin’s Java Programming Course for Beginners to learn more. It’s a 32-hour Two-way Live Online Interactive session. In addition, Henry Harvin offers a one-year Gold Membership of Coding  Academy, including e-learning access.

Moreover, this program, led by industry experts with 10+ years of experience, offers valuable perks. These include Alumni status, guaranteed internships, weekly job opportunities, and live projects. It’s a comprehensive package that ensures practical skills and continuous support for professional growth.

Frequently Asked Questions

1. Name a few alternatives to Java applets for web development.

A few alternatives to applet for web development are:

• JavaScript
• WebAssembly
• WebGL
• Web Components
• SVG and Canvas

2. Do we still use applets?

Java applets have considerably decreased in application and acceptance over the years. Several reasons, including security-related issues, can be attributed to the fall.

3. Do you have any security risks associated with Java applets?

Java applets are vulnerable to security. They can access data, download malware, etc, into an individual’s computer. 

4. Can I use Java applets on mobile devices?

Many mobile phones, such as iOS and Android, do not support applets because of safety factors. 

5. What do you mean by applet in Java?

An applet is a Java application that performs a specific task. It is embedded within a webpage and has limited functionality. This allows applets to run quickly.

Download ebook