WORKING WITH GRAPHICS

The AWT supports a rich assortment of graphics methods. All graphics are drawn
relative to a window. This can be the main window of an applet, a child window of
an applet, or a stand-alone application window. The origin of each window is at the
top-left corner and is 0,0. Coordinates are specified in pixels. All output to a window
takes place through a graphics context. A graphics context is encapsulated by the
Graphics class and is obtained in two ways:
■ It is passed to an applet when one of its various methods, such as paint( ) or
update( ), is called.
■ It is returned by the getGraphics( ) method of Component.
For the remainder of the examples in this chapter, we will be demonstrating
graphics in the main applet window. However, the same techniques will apply to any
other window.
The Graphics class defines a number of drawing functions. Each shape can be
drawn edge-only or filled. Objects are drawn and filled in the currently selected
graphics color, which is black by default. When a graphics object is drawn that exceeds
the dimensions of the window, output is automatically clipped. Let’s take a look at
several of the drawing methods.

Drawing Lines
Lines are drawn by means of the drawLine( ) method, shown here:
void drawLine(int startX, int startY, int endX, int endY)
drawLine( ) displays a line in the current drawing color that begins at startX,startY and
ends at endX,endY.
The following applet draws several lines:
// Draw lines
import java.awt.*;
import java.applet.*;
/*



*/
public class Lines extends Applet {
public void paint(Graphics g) {
g.drawLine(0, 0, 100, 100);
g.drawLine(0, 100, 100, 0);
g.drawLine(40, 25, 250, 180);
g.drawLine(75, 90, 400, 400);
g.drawLine(20, 150, 400, 40);
g.drawLine(5, 290, 80, 19);
}
}

Drawing Rectangles
The drawRect( ) and fillRect( ) methods display an outlined and filled rectangle,
respectively. They are shown here:
void drawRect(int top, int left, int width, int height)
void fillRect(int top, int left, int width, int height)
The upper-left corner of the rectangle is at top,left. The dimensions of the rectangle are
specified by width and height.
To draw a rounded rectangle, use drawRoundRect( ) or fillRoundRect( ), both
shown here:
void drawRoundRect(int top, int left, int width, int height,
int xDiam, int yDiam)

Drawing Ellipses and Circles
To draw an ellipse, use drawOval( ). To fill an ellipse, use fillOval( ). These methods
are shown here:
void drawOval(int top, int left, int width, int height)
void fillOval(int top, int left, int width, int height)
The ellipse is drawn within a bounding rectangle whose upper-left corner is specified
by top,left and whose width and height are specified by width and height.
To draw a circle, specify a square as the bounding rectangle.

Drawing Arcs
Arcs can be drawn with drawArc( ) and fillArc( ), shown here:
void drawArc(int top, int left, int width, int height, int startAngle,
int sweepAngle)
void fillArc(int top, int left, int width, int height, int startAngle,
int sweepAngle)
The arc is bounded by the rectangle whose upper-left corner is specified by top,left
and whose width and height are specified by width and height. The arc is drawn from
startAngle through the angular distance specified by sweepAngle. Angles are specified
in degrees. Zero degrees is on the horizontal, at the three o’clock position. The arc is
drawn counterclockwise if sweepAngle is positive, and clockwise if sweepAngle is
negative. Therefore, to draw an arc from twelve o’clock to six o’clock, the start angle
would be 90 and the sweep angle 180.

Drawing Polygons
It is possible to draw arbitrarily shaped figures using drawPolygon( ) and fillPolygon( ),
shown here:
void drawPolygon(int x[ ], int y[ ], int numPoints)
void fillPolygon(int x[ ], int y[ ], int numPoints)
The polygon’s endpoints are specified by the coordinate pairs contained within the x and
y arrays. The number of points defined by x and y is specified by numPoints. There are
alternative forms of these methods in which the polygon is specified by a Polygon object.