506 Chapter 15 Graphics
15.6 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., 0 degrees is in the easterly direction, and positive angles indicate counterclockwise rotation from the easterly direction); see Figure 15.11.
Listing 15.4 is an example of how to draw arcs; the output is shown in Figure 15.12.
(x, y) |
w |
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arcAngle |
h |
startAngle |
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FIGURE 15.11 The drawArc method draws an arc based on an oval with specified angles.
LISTING 15.4 DrawArcs.java
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import javax.swing.JFrame; |
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import javax.swing.JPanel; |
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import java.awt.Graphics; |
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public class DrawArcs extends JFrame { |
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public DrawArcs() { |
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setTitle("DrawArcs"); |
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add a panel |
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add(new ArcsPanel()); |
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} |
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/** Main method */ |
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public static void main(String[] args) { |
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DrawArcs frame = new DrawArcs(); |
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frame.setSize(250, 300); |
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frame.setLocationRelativeTo(null); // Center the frame |
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frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); |
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frame.setVisible(true); |
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} |
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} |
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// The class for drawing arcs on a panel |
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class ArcsPanel extends JPanel { |
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// Draw four blades of a fan |
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override paintComponent |
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protected void paintComponent(Graphics g) |
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super.paintComponent(g); |
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int xCenter = getWidth() / 2; |
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int yCenter = getHeight() / 2; |
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int radius = (int)(Math.min(getWidth(), getHeight()) * 0.4); |
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30
15.7 Drawing Polygons and Polylines 509
To draw a polyline, use the drawPolyline(int[] x, int[] y, int nPoints) method, which draws a sequence of connected lines defined by arrays of x- and y-coordinates. For example, the following code draws the polyline, as shown in Figure 15.15(b).
int x[] = {40, 70, 60, 45, 20}; int y[] = {20, 40, 80, 45, 60}; g.drawPolyline(x, y, x.length);
Listing 15.5 is an example of how to draw a hexagon, with the output shown in Figure 15.16.
LISTING 15.5 DrawPolygon.java
1 import javax.swing.JFrame;
2 import javax.swing.JPanel;
3 import java.awt.Graphics;
4 import java.awt.Polygon;
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6 public class DrawPolygon extends JFrame {
7public DrawPolygon() {
8setTitle("DrawPolygon");
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add(new PolygonsPanel()); |
add a panel |
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} |
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12/** Main method */
13public static void main(String[] args) {
14DrawPolygon frame = new DrawPolygon();
15frame.setSize(200, 250);
16frame.setLocationRelativeTo(null); // Center the frame
17frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
18frame.setVisible(true);
19}
20}
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// Draw a polygon in the panel |
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class PolygonsPanel extends JPanel { |
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protected void paintComponent(Graphics g) |
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paintComponent |
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super.paintComponent(g); |
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27int xCenter = getWidth() / 2;
28int yCenter = getHeight() / 2;
29int radius = (int)(Math.min(getWidth(), getHeight()) * 0.4);
31// Create a Polygon object
32Polygon polygon = new Polygon();
34// Add points to the polygon in this order
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polygon.addPoint(xCenter + radius, yCenter); |
add a point |
36polygon.addPoint((int)(xCenter + radius *
37Math.cos(2 * Math.PI / 6)), (int)(yCenter – radius *
38Math.sin(2 * Math.PI / 6)));
39polygon.addPoint((int)(xCenter + radius *
40Math.cos(2 * 2 * Math.PI / 6)), (int)(yCenter – radius *
41Math.sin(2 * 2 * Math.PI / 6)));
42polygon.addPoint((int)(xCenter + radius *
43Math.cos(3 * 2 * Math.PI / 6)), (int)(yCenter – radius *
44Math.sin(3 * 2 * Math.PI / 6)));
45polygon.addPoint((int)(xCenter + radius *
46Math.cos(4 * 2 * Math.PI / 6)), (int)(yCenter – radius *
47Math.sin(4 * 2 * Math.PI / 6)));
48polygon.addPoint((int)(xCenter + radius *