Exercise 12-1. Example 12-1 contains a centerText(
) method that centers one or two lines of text within a
rectangle. Write a modified version of this method that positions a
single line of text according to two new method parameters. One
parameter should specify the horizontal positioning: left-, center-,
or right-justified. The other parameter should specify the vertical
position: at the top of the rectangle, centered, or at the bottom of
the rectangle. You can use the FontMetrics class,
as Example 12-1 does, or the Java 2D
getStringBounds( ) method of the
Font class. Write a
GraphicsExample class that demonstrates all nine
possible positioning types supported by your method.
Exercise 12-2. Use the animation techniques demonstrated in this chapter to write an
applet that scrolls a textual message across the screen. The text to
scroll and the scrolling speed should be read from applet parameters
specified with <PARAM> tags in an HTML file.
Exercise 12-3. Experiment with the graphics capabilities of the
Graphics and Graphics2D
classes, and write an applet or application that displays some kind
of interesting and dynamic graphics. You may want to take your
inspiration from one of the many screensaver programs on the market.
For example, you might draw filled rectangles on the screen, using
random sizes, positions, and colors. (See Math.random(
) and java.util.Random for ways to
generate random numbers.) Feel free to use any of the custom
Shape, Stroke, or
Paint classes developed in this chapter. Be
creative!
Exercise 12-4. One of the things that makes graphics so powerful is that it gives us
the ability to visualize patterns. Look back at Example 1-15. This program computes prime numbers with the
"Sieve of Eratosthenes" algorithm,
whereby prime numbers are located by ruling out multiples of all
previous prime numbers. As part of this algorithm, you maintain an
array that specifies whether a number is prime or not. Write a
graphical version of the Sieve program. It should
display the array as a 2D matrix; cells in the matrix that represent
prime numbers should be displayed in one color, and nonprimes should
be displayed in another color. Write your program as a standalone
application or as a GraphicsExample
implementation, if you prefer.
Now extend your program again. When computing primes,
don't simply store a boolean
value to indicate whether a number is prime or not. Instead, store an
int value that specifies, for nonprime numbers,
the prime number that was used to rule this one out. After computing
a set of primes, display the contents of your array as a rectangular
grid, using a different color to indicate the multiples of each
prime. The patterns that emerge look best when viewed in a square
grid with a prime number as its height and width. For example, if you
compute all the primes up to 361, you can graphically display your
results in a square grid with 19 cells per side. Study the patterns
you see. Does it give you insight into the workings of the algorithm?
Does it help you understand why it is called a
"sieve"?
Exercise 12-5. Example 12-10 demonstrates how font glyphs can be used
as Shape objects and shows how those
Shape objects can be transformed with an arbitrary
AffineTransform object. Write a custom
Stroke object that is initialized with a
Font and a string of text. When this
Stroke class is used to draw a shape, it should
display the specified text, using the specified font, along the
outline of the specified shape. The text should hug the outline of
the shape as closely as possible, which means that each font glyph
has to be rotated, positioned, and drawn independently of the other
glyphs. Use the two-argument version of
Shape.getPathIterator( ) to obtain a
FlatteningPathIterator that approximates the shape
using straight line segments. You'll need to use
geometry to compute the slope of each line segment and trigonometry
to convert the slope to a rotation angle for each font glyph (you may
find Math.atan2( ) helpful). Write a
GraphicsExample class that displays some text art
that demonstrates your new Stroke object.
