e590. drawing a pie chart.txt

这里面包含了一百多个JAVA源文件

This example implements a method for drawing a pie chart. 
    // Class to hold a value for a slice
    public class PieValue {
        double value;
        Color color;
    
        public PieValue(double value, Color color) {
            this.value = value;
            this.color = color;
        }
    }
    
    // slices is an array of values that represent the size of each slice.
    public void drawPie(Graphics2D g, Rectangle area, PieValue[] slices) {
        // Get total value of all slices
        double total = 0.0D;
        for (int i=0; i<slices.length; i++) {
            total += slices[i].value;
        }
    
        // Draw each pie slice
        double curValue = 0.0D;
        int startAngle = 0;
        for (int i=0; i<slices.length; i++) {
            // Compute the start and stop angles
            startAngle = (int)(curValue * 360 / total);
            int arcAngle = (int)(slices[i].value * 360 / total);
    
            // Ensure that rounding errors do not leave a gap between the first and last slice
            if (i == slices.length-1) {
                arcAngle = 360 - startAngle;
            }
    
            // Set the color and draw a filled arc
            g.setColor(slices[i].color);
            g.fillArc(area.x, area.y, area.width, area.height, startAngle, arcAngle);
    
            curValue += slices[i].value;
        }
    }

Here's some code that uses the drawPie() method: 
    class MyComponent extends JComponent {
        PieValue[] slices = new PieValue[4];
    
        MyComponent() {
            slices[0] = new PieValue(25, Color.red);
            slices[1] = new PieValue(33, Color.green);
            slices[2] = new PieValue(20, Color.pink);
            slices[3] = new PieValue(15, Color.blue);
        }
    
        // This method is called whenever the contents needs to be painted
        public void paint(Graphics g) {
            // Draw the pie
            drawPie((Graphics2D)g, getBounds(), slices);
        }
    }

    // Show the component in a frame
    JFrame frame = new JFrame();
    frame.getContentPane().add(new MyComponent());
    frame.setSize(300, 200);
    frame.setVisible(true);