Java Applet Programming Interview Preparation Guide

Java Applet Programming Interview Questions and Answers will guide us now that a Java applet is an applet delivered to the users in the form of Java bytecode. Java applets can run in a Web browser using a Java Virtual Machine (JVM), or in Sun's AppletViewer, a stand-alone tool for testing applets. Learn Java Applet Programming or get preparation of Java Applet by the help of this Java Applet Programming Interview Questions with Answers guide

26 Java Applet Questions and Answers:

1 :: What is an Applet? Should applets have constructors?

Applets are small programs transferred through Internet, automatically installed and run as part of web-browser. Applets implements functionality of a client. Applet is a dynamic and interactive program that runs inside a Web page displayed by a Java-capable browser. We don’t have the concept of Constructors in Applets. Applets can be invoked either through browser or through Appletviewer utility provided by JDK.

2 :: How will you initialize an Applet?

Write my initialization code in the applets init method or applet constructor.

3 :: How to insert your applets into FrontPage?

1. Place the .class file in the directory containing the HTML document into which you want to insert the applet.
2. Copy the <applet>...</applet> tag from your applet implementation or examples to the clipboard.
3. In FrontPage select the "HTML" tab from the lower left hand corner.
4. Paste the <applet>...</applet> tag in an appropriate place between the <body> and </body> tags. You'll find a gray box with the aqua letter "J" in the "Normal" view indicating the the applet tag has been inserted.
5. To see the applet appearance select the "Preview" tab.

4 :: In our URLs and in the text of the buttons we have comma. Its causing an error. Is there a way to change the delimiting character for the menu arguments?

Since 2.00 version our applets support an user-defined delimiter for the menu arguments. To modify the default delimiter add the following parameter (you can use any character as a delimiter):

<param name="delimiter" value="~">

and use it within "menuItems":

<param name="menuItems" value="
{Features, Setup~}

5 :: What is the order of method invocation in an Applet?

► public void init() : Initialization method called once by browser.
► public void start() : Method called after init() and contains code to start processing. If the user leaves the page and returns without killing the current browser session, the start () method is called without being preceded by init ().
► public void stop() : Stops all processing started by start (). Done if user moves off page.
► public void destroy() : Called if current browser session is being terminated. Frees all resources used by applet.

6 :: What are the Applets Life Cycle methods? Explain them?

methods in the life cycle of an Applet:

► init() method - called when an applet is first loaded. This method is called only once in the entire cycle of an applet. This method usually intialize the variables to be used in the applet.
► start( ) method - called each time an applet is started.
► paint() method - called when the applet is minimized or refreshed. This method is used for drawing different strings, figures, and images on the applet window.
► stop( ) method - called when the browser moves off the applet’s page.
► destroy( ) method - called when the browser is finished with the applet.

7 :: What is the sequence for calling the methods by AWT for applets?

When an applet begins, the AWT calls the following methods, in this sequence:

► init()
► start()
► paint()

When an applet is terminated, the following sequence of method calls takes place :

► stop()
► destroy()

8 :: How do Applets differ from Applications?

Following are the main differences:
Application: Stand Alone, doesn’t need
web-browser. Applet: Needs no explicit installation on local machine. Can be transferred through Internet on to the local machine and may run as part of web-browser. Application: Execution starts with main() method. Doesn’t work if main is not there. Applet: Execution starts with init() method. Application: May or may not be a GUI. Applet: Must run within a GUI (Using AWT). This is essential feature of applets.

9 :: Can we pass parameters to an applet from HTML page to an applet? How?

We can pass parameters to an applet using <param> tag in the following way:

► <param name=”param1″ value=”value1″>
► <param name=”param2″ value=”value2″>

Access those parameters inside the applet is done by calling getParameter() method inside the applet. Note that getParameter() method returns String value corresponding to the parameter name.

10 :: How do we read number information from my applets parameters, given that Applets getParameter() method returns a string?

Use the parseInt() method in the Integer Class, the Float(String) constructor or parseFloat() method in the Class Float, or the
Double(String) constructor or parseDoulbl() method in the class Double.