Day 9: Making Programs Look Good with
Graphics, Fonts, and Color
NOTES AND CORRECTIONS
- On Page 226 in the section on drawing arcs, it states that "the
number of degrees traveled by the arc is specified in a clockwise
direction by using positive numbers. This is the opposite of the way a
non-2D arc is handled." This is true of beta versions of JDK 1.2,
but was corrected for the final release. The number of degrees
traveled is specified in a counterclockwise direction.
- In Listing 9.5, Lines 15-16, if you're not using a beta version of
JDK 1.2, one of the arguments should be changed from 180 to -180 so
that the arcs look like ocean waves and match Figure 9.17. The correct
lines are the following:
- Arc2D.Float wave = new Arc2D.Float(ax, ay,
10, 10, 0, -180, Arc2D.OPEN);
- Q: I am confused by what the lowercase "f" is
referring to in Day 9 on page 227 and elsewhere in the chapter. It is
added to coordinates, as in the polly method polly.moveTo(5f,
0f). Why is the "f" used for these coordinates and not
those for the arc on page 226, and why is a capital "F" used
elsewhere, such as the fl method fl.moveTo(10F, 12F)?
Help me with all these Fs and fs!
A: The F and f indicate that a number is a floating-point
number rather than an integer, and they can be used interchangeably.
If you don't use one of them, the Java compiler will assume that the
number is an int value. Many methods and constructors in Java
require floating-point arguments but can handle integers, because an
integer can be converted to floating-point without changing its value.
For this reason, constructors like Arc2D.Float() on Page 226
can use arguments such as 10 and 180 instead of 10F and 180F.
- Q: The Map2D applet compiles and can be run within
appletviewer, but it won't run in either the current Netscape
Navigator or Microsoft Internet Explorer. Why is this the case when
other applets will run?
A: Map2D won't run outside of appletviewer because it's one
of several applets in the book that requires a Java 1.2-capable
browser. Neither Navigator nor Internet Explorer supports 1.2 fully at
this time, so Sun has developed a Java
Plug-in that enhances their built-in Java support.
The Plug-in is a Java interpreter that can be used as an alternative
to the Java interpreters included with Navigator and Internet
Explorer. A Java programmer uses a modified <APPLET> tag
to make the Java Plug-in run the applet if the plug-in is present on a
user's system (if not, the plug-in can be immediately installed).
Sun has created an HTML
Converter that will read an .html file containing applets
and convert the HTML so that the applets use the Java Plug-in.
None of the book's .html files have been modified to call the
Java Plug-in, so they're being added to this Web site as time permits.
The first example is Map2D_plugin.html.