Beginning Java 2- JDK 1.3 Version
Images and Animation
Here's the code for the Hands inner class to the
NewClock class:
// Class defining the hands on the clock
class Hands extends JPanel
{
public Hands(int clockDiameter)
{
center = new Ellipse2D.Double(-3,-3,6,6); // Central boss
hourHand = new Line2D.Double(0,6,0,-clockDiameter*0.25);
minuteHand = new Line2D.Double(0,8,0,-clockDiameter*0.3);
secondHand = new Line2D.Double(0,14,0,-clockDiameter*0.35);
setOpaque(false); // Set transparent
}
// Paint the hands
public void paint(Graphics g)
{
// Get hand angles for the current time
double secondAngle = seconds*TWO_PI/60;
double minuteAngle = (secondAngle+minutes*TWO_PI)/60;
double hourAngle = (minuteAngle+hours*TWO_PI)/12;
Dimension size = getSize();
Graphics2D g2D = (Graphics2D)g;
g2D.setPaint(CLEAR); // Transparent color
g2D.fillRect(0,0,size.width,size.height); // Fill to erase
g2D.setPaint(Color.darkGray); // Hands color
g2D.translate(size.width/2, size.height/2);// Origin to center
AffineTransform transform = g2D.getTransform(); // Save this xform
// Draw hour hand
g2D.setStroke(widePen); // Use wide pen
g2D.rotate(hourAngle); // Rotate to hour position
g2D.draw(hourHand); // and draw hand
// Draw minute hand
g2D.setTransform(transform); // Reset transform
g2D.rotate(minuteAngle); // Rotate to minute position
g2D.draw(minuteHand); // and draw hand
// Draw second hand
g2D.setStroke(narrowPen); // Use narrow pen
g2D.setTransform(transform); // Reset transform
g2D.rotate(secondAngle); // Rotate to second position
g2D.draw(secondHand); // and draw hand
g2D.setPaint(Color.white); // Center color
g2D.draw(center); // Draw center
}
Line2D.Double hourHand;
Line2D.Double minuteHand;
Line2D.Double secondHand;
Ellipse2D.Double center;
final Color CLEAR = new Color(0,0,0,0);
}
The constructor is quite straightforward. The central boss holding the
hands on is the Ellipse2D.Double object, center.
This is a circle with a diameter of 6. After defining the lines
representing the hands, we call setOpaque() for the panel to
make the panel transparent.
The paint() method looks like a lot of code, but after
calculating the angular position for each hand, it is just a series of
separate drawing operations. The position of each hand is basically a
proportion of 2ϖ. Each second or minute contributes one sixtieth of
2ϖ to the position of the corresponding hand and each hour is one
twelfth. To the angular position of the minute hand we add the contribution
that the angle of the second hand represents as a fraction of a minute, and
for the hour hand we add the contribution of the minute hand. After getting
the size of the panel, we fill the entire panel with the color
CLEAR. This is to erase the previous instance of the hands
drawn on the panel. This Color object is defined as a constant
member of the class. The first three arguments to the Color
constructor define the red, green, and blue color components of the color
to be zero. The fourth argument defines something called the alpha
component for the color as zero, which defines this color as
completely transparent. We will go into the significance of the alpha
component in more detail later in this chapter. We'll just use it for now.
We want the color to be transparent because the Hands panel
will be displayed on top of the ClockFace panel in the applet,
and we want the face to be visible.
After moving the origin to the center of the panel we save the current
transform. This will enable us to restore this position after rotating the
axes to position each hand. Each hand is drawn in essentially the same way.
The Stroke for the hand is set, then the axes are rotated to
the required angle, and finally we draw the line representing the hand. The
last step after drawing the three hands is to draw the central boss in
white.
Now we have the inner classes for the face and hands defined, we are ready
to complete the applet.
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