testpolygon.java

此源码为机械工业出版社出版的《Java语言程序设计》第三版所配套的书中所有源代码。

// TestPolygon.java: Demonstrate drawing polygons
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Graphics;
import java.awt.Polygon;

public class TestPolygon extends JFrame
{
  // Default constructor
  public TestPolygon()
  {
    setTitle("Show Polygon");
    getContentPane().add(new PolygonsPanel());
  }

  // Main method
  public static void main(String[] args)
  {
    TestPolygon frame = new TestPolygon();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(200, 250);
    frame.setVisible(true);
  }
}

// Draw a polygon in the panel
class PolygonsPanel extends JPanel
{
  public void paintComponent(Graphics g)
  {
    super.paintComponent(g);

    int xCenter = getWidth()/2;
    int yCenter = getHeight()/2;
    int radius =
      (int)(Math.min(getSize().width, getSize().height)*0.4);

    // Create a Polygon object
    Polygon polygon = new Polygon();

    // Add points to the polygon
    polygon.addPoint(xCenter + radius, yCenter);
    polygon.addPoint((int)(xCenter + radius*Math.cos(2*Math.PI/6)),
      (int)(yCenter - radius*Math.sin(2*Math.PI/6)));
    polygon.addPoint((int)(xCenter + radius*Math.cos(2*2*Math.PI/6)),
      (int)(yCenter - radius*Math.sin(2*2*Math.PI/6)));
    polygon.addPoint((int)(xCenter + radius*Math.cos(3*2*Math.PI/6)),
      (int)(yCenter - radius*Math.sin(3*2*Math.PI/6)));
    polygon.addPoint((int)(xCenter + radius*Math.cos(4*2*Math.PI/6)),
      (int)(yCenter - radius*Math.sin(4*2*Math.PI/6)));
    polygon.addPoint((int)(xCenter + radius*Math.cos(5*2*Math.PI/6)),
      (int)(yCenter - radius*Math.sin(5*2*Math.PI/6)));

    // Draw the polygon
    g.drawPolygon(polygon);
  }
}