Java How to Program Fourth Edition - DCC

120 Introduction to Java Applets Chapter 3
Software Engineering Observation 3.2
Generally, each applet should be less than 800 pixels wide and 600 pixels tall (most computer
screens support these dimensions as the minimum width and height). 3.2
Common Programming Error 3.3
Placing additional characters such as commas (,) between the attributes in the
tag may cause the appletviewer or browser to produce an error message indicating a
MissingResourceException when loading the applet. 3.3
Common Programming Error 3.4
Forgetting the ending tag prevents the applet from loading into the appletviewer
or browser properly. 3.4
Testing and Debugging Tip 3.5
If you receive a MissingResourceException error message when loading an applet
into the appletviewer or a browser, check the tag in the HTML file carefully
for syntax errors. Compare your HTML file to the file in Fig. 3.7 to confirm proper syntax. 3.5
The appletviewer understands only the and HTML
tags, so it is sometimes referred to as the “minimal browser” (it ignores all other HTML
tags). The appletviewer is an ideal place to test an applet and ensure that it executes
properly. Once the applet’s execution is verified, you can add the applet’s HTML tags to
an HTML file that will be viewed by people browsing the Internet.
To execute the WelcomeApplet in the appletviewer open a command window,
change to the directory containing your applet and HTML file and type the command
appletviewer WelcomeApplet.html
Note that the appletviewer requires an HTML file to load an applet. This is different
from the java interpreter for applications which requires only the class name of the application
class. Also, the preceding command must be issued from the directory in which the
HTML file and the applet’s .class file are located.
Common Programming Error 3.5
Running the appletviewer with a file name that does not end with .html or .htm is an
error that prevents the appletviewer from loading your applet for execution. 3.5
Portability Tip 3.2
Test your applets in every browser used by people who view your applet. This will help ensure
that people who view your applet experience the functionality you expect. [Note: A goal
of the Java Plug-In (discussed later in the book) is to provide consistent applet execution
across many different browsers.] 3.2
3.4 Two More Simple Applets: Drawing Strings and Lines
Let us consider another applet. An applet can draw Welcome to Java Programming!
several ways. For example, an applet can use two drawString statements in method
paint to print multiple lines of text as in Fig. 3.8. The HTML file to load the applet into
an applet container is shown in Fig. 3.9.
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