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Java基础之在窗口中绘图——绘制曲线（CurveApplet 1）

2013-12-24 00:09 429 查看

Applet程序。

定义自由曲线的类有两个，其中一个定义二次曲线，另一个定义三次曲线。这些自由曲线是用一系列线段定义的参数化曲线。二次曲线段用方程定义，方程包含独立变量x的平方。三次曲线也用方程定义，方程包含独立变量x的立方。

QuadCurve2D:二次曲线的抽象基类，曲线用两个端点和一个用来定义两端切线的控制点来定义。切线是从端点到控制点的直线。

CubicCurve2D:三次曲线的抽象基类，曲线用两个端点和两个用来定义两端切线的控制点来定义。切线是从端点到对应控制点的直线。

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;

@SuppressWarnings("serial")
public class CurveApplet extends JApplet {
// Initialize the applet
@Override
public void init() {
pane = new CurvePane();                                            // Create pane containing curves
Container content = getContentPane();                              // Get the content pane

// Add the pane displaying the curves to the content pane for the applet
content.add(pane);                                                 // BorderLayout.CENTER is default position
}

// Class defining a pane on which to draw
class CurvePane extends JComponent {
// Constructor
public CurvePane() {
quadCurve = new QuadCurve2D.Double(                              // Create quadratic curve
startQ.x, startQ.y,                              // Segment start point
control.x, control.y,                            // Control point
endQ.x, endQ.y);                                 // Segment end point

cubicCurve = new CubicCurve2D.Double(                            // Create cubic curve
startC.x, startC.y,                              // Segment start point
controlStart.x, controlStart.y,                  // Control pt for start
controlEnd.x, controlEnd.y,                      // Control point for end
endC.x, endC.y);                                 // Segment end point
}

@Override
public void paint(Graphics g) {
Graphics2D g2D = (Graphics2D)g;                                  // Get a 2D device context

// Draw the curves
g2D.setPaint(Color.BLUE);
g2D.draw(quadCurve);
g2D.draw(cubicCurve);
}
}

// Points for quadratic curve
private Point2D.Double startQ = new Point2D.Double(50, 75);          // Start point
private Point2D.Double endQ = new Point2D.Double(150, 75);           // End point
private Point2D.Double control = new Point2D.Double(80, 25);         // Control point

// Points for cubic curve
private Point2D.Double startC = new Point2D.Double(50, 150);         // Start point
private Point2D.Double endC = new Point2D.Double(150, 150);          // End point
private Point2D.Double controlStart = new Point2D.Double(80, 100);   // 1st cntrl point
private Point2D.Double controlEnd = new Point2D.Double(160, 100);    // 2nd cntrl point
private QuadCurve2D.Double quadCurve;                                // Quadratic curve
private CubicCurve2D.Double cubicCurve;                              // Cubic curve
private CurvePane pane = new CurvePane();                            // Pane to contain curves
}

<html>
<head>
</head>
<body bgcolor="000000">
<center>
<applet
code    = "CurveApplet.class"
width    = "300"
height    = "300"
>
</applet>
</center>
</body>
</html>

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