自考JAVA语言程序设计(一)课后习题答案和源代码(第七章)

第七章

7.1 编写一个应用程序，绘制一个五角星。

程序运行结果：

源文件：Work7_1.java

import java.awt.*;

import javax.swing.*;

/**

*7.1画一个五角星

*@author黎明你好

*/

public class Work7_1

{

public static void main(String args[])

{

JFrame win = new JFrame("第七章，第一题");

win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

win.setBounds(50, 50, 210, 250);

win.add(new FiveStarCanvas(100), BorderLayout.CENTER);

win.setVisible(true);

win.validate();

}

}

画板类源文件: FiveStarCanvas.java

/**

*画板类，在上面画出五角星

*@author黎明你好

*/

class FiveStarCanvas extends Canvas

{

private static final long serialVersionUID = 1L;

/**五角星外接圆的半径*/

private int radius;

/**

*构造方法

*@param r-初始化外接圆半径

*/

public FiveStarCanvas(int r)

{

this.radius = r;

}

public void paint(Graphics g)

{

int ax = radius; int ay = 0;

int bx = (int) (radius * (1 - Math.cos((18 * Math.PI) / 180)));

int cx = (int) (radius * (1 + Math.cos((18 * Math.PI) / 180)));

int dx = (int) (radius * (1 - Math.cos((54 * Math.PI) / 180)));

int ex = (int) (radius * (1 + Math.cos((54 * Math.PI) / 180)));

int by = (int) (radius * (1 - Math.sin((18 * Math.PI) / 180)));

int cy = (int) (radius * (1 - Math.sin((18 * Math.PI) / 180)));

int dy = (int) (radius * (1 + Math.sin((54 * Math.PI) / 180)));

int ey = (int) (radius * (1 + Math.sin((54 * Math.PI) / 180)));

g.setColor(Color.RED);

g.drawLine(dx, dy, ax, ay);

g.drawLine(ax, ay, ex, ey);

g.drawLine(ex, ey, bx, by);

g.drawLine(bx, by, cx, cy);

g.drawLine(cx, cy, dx, dy);

g.setColor(Color.BLUE);

g.drawOval(0, 0, 2 * radius, 2 * radius);

g.drawLine(radius, radius, ax, ay);

g.drawLine(radius, radius, bx, by);

g.drawLine(radius, radius, cx, cy);

g.drawLine(radius, radius, dx, dy);

g.drawLine(radius, radius, ex, ey);

}

}

7.2 用Graphics2D绘制一条抛物线，设抛物线方程的系数从图形界面输入。

程序运行结果：

frame源文件：ParabolaFrame.java

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

/**

*7.2用Graphics2D画抛物线，抛物线方程的系数从图形界面输入.

*@author黎明你好

*/

public class ParabolaFrame extends JFrame implements ActionListener {

private static final long serialVersionUID = 1L;

private ParabolaCanvas canvas;// 画出抛物线的花瓣

private JTextField inputA_text, inputB_text, inputC_text; // 三个文本框，接收方程系数

private JButton confirm_button;// 确定按钮

private JLabel display_label;

private JPanel panel;// 布局面板

private double a, b, c;// 抛物线三个系数

public ParabolaFrame()

{

super("第七章，第二题");

a = 1;

b = 0;

c = 0;

panel = new JPanel();

canvas = new ParabolaCanvas(a, b, c);

inputA_text = new JTextField("" + a, 3);

inputB_text = new JTextField("" + b, 3);

inputC_text = new JTextField("" + c, 3);

confirm_button = new JButton("确定");

display_label = new JLabel();

panel.add(new JLabel("a = "));