Essential Java Applet Interview Questions & Answers:

1. What type of sound file formats can I use for the applets?

Java v1.02 only supports the "voice format" of the .au sound files. This is also know as "µ-law, 8/16-bit, mono, 8000hz sample rate"

2. Why do you Canvas?

The Canvas class of java.awt is used to provide custom drawing and event handling. It provides a general GUI component for drawing images and text on the screen. It does not support any drawing methods of its own, but provides access to a Graphics object through its paint() method. The paint() method is invoked upon the creation and update of a canvas so that the Graphics object associated with a Canvas object can be updated.

3. What is Difference between AWT and Swing?

Swing provides a richer set of components than AWT. They are 100% Java-based. AWT on the other hand was developed with the mind set that if a component or capability of a component werent available on one platform, it wouldnt be available on any platform. Due to the peer-based nature of AWT, what might work on one implementation might not work on another, as the peer-integration might not be as robust. There are a few other advantages to Swing over AWT:

► Swing provides both additional components and added functionality to AWT-replacement components
► Swing components can change their appearance based on the current "look and feel" library that's being used.
► Swing components follow the Model-View-Controller (MVC) paradigm, and thus can provide a much more flexible UI.
► Swing provides "extras" for components, such as:
► Icons on many components
► Decorative borders for components
► Tool tips for components
► Swing components are lightweight (less resource intensive than AWT)
► Swing provides built-in double buffering
► Swing provides paint debugging support for when you build your own components

Swing also has a few disadvantages:
► It requires Java 2 or a separate JAR file
► If you're not very careful when programming, it can be slower than AWT (all components are drawn)
► Swing components that look like native components might not act exactly like native components

4. What is the base class for all swing components?

JComponent (except top-level containers)

5. How do you communicate in between Applets and Servlets?

We can use the java.net.URLConnection and java.net.URL classes to open a standard HTTP connection and "tunnel" to the web server. The server then passes this information to the servlet in the normal way. Basically, the applet pretends to be a web browser, and the servlet doesn't know the difference. As far as the servlet is concerned, the applet is just another HTTP client.

6. How will you communicate between two Applets?

The simplest method is to use the static variables of a shared class since there's only one instance of the class and hence only one copy of its static variables. A slightly more reliable method relies on the fact that all the applets on a given page share the same AppletContext. We obtain this applet context as follows:

AppletContext ac = getAppletContext();

AppletContext provides applets with methods such as getApplet(name), getApplets(),getAudioClip, getImage, showDocument and showStatus().

7. When is update method called?

Whenever a screen needs redrawing (e.g., upon creation, resizing, validating) the update method is called. By default, the update method clears the screen and then calls the paint method, which normally contains all the drawing code.

8. Which method is used to output a string to an applet? Which function is this method included in?

drawString( ) method is used to output a string to an applet. This method is included in the paint method of the Applet.

9. What are the steps involved in Applet development?

Following are the steps involved in Applet development:

► Create/Edit a Java source file. This file must contain a class which extends Applet class.
► Compile your program using javac
► Execute the appletviewer, specifying the name of your applet's source file or html file. In case the applet information is stored in html file then Applet can be invoked using java enabled web browser.

10. What are the Applets information methods?

The following are the Applet's information methods: getAppletInfo() method: Returns a string describing the applet, its author, copyright information, etc. getParameterInfo( ) method: Returns an array of string describing the applet's parameters.