14.5. Key Events

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13.8. Drawing Arcs

An arc is conceived as part of an oval bounded by a rectangle. The methods to draw or fill an arc are as follows :

 drawArc(   int   x,   int   y,   int   w,   int   h,   int   startAngle,   int   arcAngle); fillArc(   int   x,   int   y,   int   w,   int   h,   int   startAngle,   int   arcAngle); 

Parameters x , y , w , and h are the same as in the drawOval method; parameter startAngle is the starting angle; arcAngle is the spanning angle (i.e., the angle covered by the arc). Angles are measured in degrees and follow the usual mathematical conventions (i.e., degrees is in the easterly direction, and positive angles indicate counterclockwise rotation from the easterly direction); see Figure 13.11.

Figure 13.11. The drawArc method draws an arc based on an oval with specified angles.

Listing 13.6 is an example of how to draw arcs; the output is shown in Figure 13.12.

Figure 13.12. The program draws four filled arcs.

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Listing 13.6. DrawArcs.java

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 1   import   javax.swing.JFrame; 2   import   javax.swing.JPanel; 3   import   java.awt.Graphics; 4 5   public class   DrawArcs   extends   JFrame { 6   public   DrawArcs() { 7 setTitle(   "DrawArcs"   ); 

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 8 add(   new   ArcsPanel()); 9 } 10 11  /** Main method */  12   public static void   main(String[] args) { 13 DrawArcs frame =   new   DrawArcs(); 14 frame.setLocationRelativeTo(   null   );  // Center the frame  15 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 16 frame.setSize(   250   ,   300   ); 17 frame.setVisible(   true   ); 18 } 19 } 20 21  // The class for drawing arcs on a panel  22   class   ArcsPanel   extends   JPanel { 23  // Draw four blazes of a fan  24    protected void   paintComponent(Graphics g)  { 25    super.paintComponent(g);    26 27   int   xCenter = getWidth() /   2   ; 28   int   yCenter = getHeight() /   2   ; 29   int   radius = (   int   )(Math.min(getWidth(), getHeight()) *     .   4   ); 30 31   int   x = xCenter - radius; 32   int   y = yCenter - radius; 33 34  g.fillArc(x, y,   2   * radius,   2   * radius,     ,   30   );  35  g.fillArc(x, y,   2   * radius,   2   * radius,   90   ,   30   );  36  g.fillArc(x, y,   2   * radius,   2   * radius,   180   ,   30   );  37  g.fillArc(x, y,   2   * radius,   2   * radius,   270   ,   30   );  38 } 39 } 

Note

Angles may be negative. A negative starting angle sweeps clockwise from the easterly direction, as shown in Figure 13.13. A negative spanning angle sweeps clockwise from the starting angle. The following two statements draw the same arc:

 g.fillArc(x, y,   2   * radius,   2   * radius,   -30   ,   -20   ); g.fillArc(x, y,   2   * radius,   2   * radius,   -50   ,   20   ); 

Figure 13.13. Angles may be negative.

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The first statement uses negative starting angle -30 and negative spanning angle -20 as shown in Figure 13.13(a). The second statement uses negative starting angle -50 and positive spanning angle 20, as shown in Figure 13.13(b).