20 Java Applet Interview Questions and Answers

Java Applet is a type of program that is designed to be run on a Java-compatible web browser. Applets are usually small programs that perform a specific task or function. If you are applying for a position that involves Java Applet, you should expect to be asked questions about your experience and knowledge during the interview process. In this article, we will review some common Java Applet interview questions and provide tips on how to answer them.

Java Applet Interview Questions and Answers

Here are 20 commonly asked Java Applet interview questions and answers to prepare you for your interview:

1. What is an applet in Java?

An applet is a small Java program that can be embedded in a web page. Applets are used to make web pages more interactive and can perform tasks such as animating images, calculating formulas, or checking usernames and passwords.

2. Can you explain the lifecycle of a java applet?

The lifecycle of a java applet is as follows:

1. The applet is loaded into memory and initialized.
2. The applet’s start() method is called.
3. The applet’s paint() method is called.
4. The applet’s stop() method is called.
5. The applet’s destroy() method is called.
6. The applet is unloaded from memory.

3. What are the differences between an application and an applet?

The main difference between an application and an applet is that an applet is designed to be run within a web browser, while an application is not. Applets also have some restrictions placed on them in terms of what they are allowed to do, for security reasons.

4. How do you use threading with Applets to make them more efficient?

Threading can be used with Applets to make them more efficient by allowing multiple tasks to be performed simultaneously. For example, if you have an Applet that is responsible for both drawing images and playing sound, you can use threading to have the Applet perform both tasks at the same time. This can help to improve the overall performance of the Applet.

5. What’s the difference between the Applet class and the Panel class?

The Applet class is a subclass of the Panel class, meaning that it inherits all of the Panel class’s methods and variables. The Applet class also adds a few methods of its own, specifically related to loading and running the applet within a web browser.

6. Can you give me some examples of real-world applications that use Applets?

There are a few examples of real-world applications that use Applets. One example is an online banking application that uses an Applet to provide a secure connection for customers to log in and access their accounts. Another example is an online shopping application that uses an Applet to provide a secure connection for customers to enter their credit card information.

7. What is the best way to create multiple threads for an Applet?

The best way to create multiple threads for an Applet is to use the Thread class.

8. What is the significance of init() method in Applet?

The init() method is called when an Applet is first loaded. This is where you should initialize any variables that will be used by the Applet.

9. Why isn’t it a good idea to override paint() or update() methods directly?

Overriding the paint() or update() methods directly can lead to problems because they are both called automatically by the system. If you override them, then you can end up with a situation where your code is executed at unexpected times, which can lead to errors. It is better to instead use a method like paintComponent() that is only called when you explicitly request it.

10. When should we stop using Applets in our web applications?

While applets can provide a richer user experience than traditional web applications, they require the user to have a Java runtime installed on their machine. With the rise of HTML5 and other web technologies, there are now other ways to provide a similar user experience without the need for a Java runtime. As such, it is generally recommended that developers stop using applets in their web applications.

11. Is it possible to communicate between two different Applets running on the same page? If yes, then how?

Yes, it is possible to communicate between two different Applets running on the same page. One way to do this is to use the getAppletContext() method, which returns an AppletContext object. This object can be used to call the other Applet’s methods.

12. Is it possible to load one Applet from another Applet? If yes, then how?

Yes, it is possible to load one Applet from another Applet. This can be done using the getAppletContext().showDocument() method. This method takes as input an Applet URL, which specifies the Applet to be loaded.

13. How can you pass parameters to Applets?

You can pass parameters to an Applet in two ways:

1. By using the tag inside the HTML code that embeds the Applet.
2. By using the AppletContext.showDocument() method.

14. What are the common mistakes made by developers when implementing Applets?

The most common mistake is not properly handling security when loading resources from other domains. Another common mistake is not properly handling the Applet’s lifecycle, which can lead to memory leaks.

15. What are the ways to resize an Applet?

There are a few ways to resize an Applet. One way is to simply change the size of the Applet’s container. Another way is to override the Applet’s getPreferredSize() method to return the desired size. Finally, some Applet containers provide methods to resize the Applet directly.

16. What is the role of the destroy() method in an Applet?

The destroy() method is called when an Applet is no longer needed. It is used to release resources that the Applet is using, such as images or sounds.

17. Can you explain what a trusted Applet is?

A trusted Applet is an Applet that has been granted permission to access certain resources that are normally restricted. This permission is granted by the user, and it is up to the Applet to request it. Once an Applet has been granted trusted status, it can then access things like the user’s file system and network resources.

18. What are signed Applets and unsigned Applets?

A signed Applet is an Applet that has been signed with a digital certificate that verifies the identity of the author. An unsigned Applet is an Applet that has not been signed and therefore its identity has not been verified.

19. What are the advantages of Applets over Servlets?

Applet advantages include the ability to run on the client side, which can result in improved performance and a more responsive user interface. Additionally, Applets have access to a wider range of client-side resources, such as the user’s file system.

20. How can you avoid security risks when working with Applets?

When working with Applets, it is important to be aware of the potential security risks. One way to avoid these risks is to only run Applets from trusted sources. Additionally, you can configure your browser to only allow signed Applets to run. This will help to ensure that the Applet has not been tampered with and that it is coming from a trusted source.