Download the JDK
Search the Tutorials
Trail: Deployment
Lesson: Applets
Home Page > Deployment > Applets
Answers to Questions and Exercises: Java Applets

### Questions

> 1. Question: Which classes can an applet extend?

>    Answer: An applet can extend the `java.applet.Applet` class or the `java.swing.JApplet` class.

>    The `java.applet.Applet` class extends the `java.awt.Panel` class and enables you to use the GUI tools in the AWT package.

>    The `java.swing.JApplet` class is a subclass of `java.applet.Applet` that also enables you to use the Swing GUI tools.

> 2. Question: How do you cause the applet GUI in the browser to be refreshed when data in it may have changed?

>    Answer: You invoke the `repaint()` method. This method causes the `paint` method, which is required in any applet, to be invoked again, updating the display.

> 3. Question: For what do you use the `start()` method?

>    Answer: You use the `start()` method when the applet must perform a task after it is initialized, before receiving user input. The `start()` method either performs the applet's work or (more likely) starts up one or more threads to perform the work.

> 4. Question: True or false: An applet can make network connections to any host on the Internet.

>    Answer: False: An applet can only connect to the host that it came from.

> 5. Question: How do you get the value of a parameter specified in the `APPLET` tag from within the applet's code?

>    Answer: You use the `getParameter("Parameter name")` method, which returns the String value of the parameter.

> 6. Question: True of false: An applet can run multiple threads.

>    Answer: True. The `paint` and `update` methods are always called from the AWT drawing and event handling thread. You can have your applet create additional threads, which is recommended for performing time-consuming tasks.

> 7. Question: Match the following tag names with the descriptions in the following lists:
>    1. `EMBED` tag
>    2. `APPLET` tag
>    3. `OBJECT` tag

>    1. Use to deploy applets to a multi-browser environment.
>    2. Use to deploy applets that are to be used only with the Mozilla family of browsers
>    3. Use to deploy applets that are to be used only with Internet Explorer

>    Answer:

>    1. `EMBED` tag: b
>    2. `APPLET` tag: a
>    3. `OBJECT` tag: c

### Exercises

> 1. Exercise: For an applet using the `Exercise` class, write the `Applet` tag that sets the `ButtonName` parameter to `Save`.

>    Answer:

>    >     <APPLET CODE=AppletButton.class>
>    >       <PARAM NAME=ButtonName VALUE=Save>
>    >     </APPLET>

> 2. Exercise: Write the method to display an applet in the browser, so that the contents are contained in a rectangle around the phrase "Exercise Applet". Have the applet be one pixel less than the size specified ont he web page, and the phrase starting at the coordinates 5, 15.

>    Answer:

>    >     public void paint(Graphics g) {
>    >     	//Draw a Rectangle around the applet's display area.
>    >             g.drawRect(0, 0,
>    >     		   getWidth() - 1,
>    >     		   getHeight() - 1);

>    >     	//Draw the current string inside the rectangle.
>    >             g.drawString("Exercise Applet", 5, 15);
>    >         }

Previous page: Questions and Exercises: Java Applets