《Java语言程序设计》的课程作业

前言：学习编程刚开始最合适的资料可能是一些现成的 bug-free 代码。由浅入深自己慢慢琢磨，对代码进行编译运行，到修改尝试，到改写添加新功能，到能够独立写出自己的程序。这学期选了门 Java，虽然没上过几节课，不过作业还算是马马虎虎的完成了，贴出来便于今后初学者参考。由于我初学 Java，不能保证代码的编程风格和效率，仅供参考吧。

学习 Java 一开始得确保自己的电脑上有 JRE (Java Runtime Environment)，这样才能跑程序。可以去官网下一个，设置好环境变量后通过 command window 进行类 dos 命令的操作：将写好的 Java 程序保存为文本文件 .java，cd 到文件目录下之后 javac test.java（编译），生成 .class 文件。然后 java test 即可运行程序。

对于初学者更为推荐的是 eclipse，这是功能强大的集成环境，其实也不光可以用来写 Java 程序。另外在设计图形用户界面时也可以使用 NetBeans，这是类似 Visual Basic 的所见即所得的编辑软件。在 eclipse 下面新建工程等操作在网上查一下就ok。下面列出这学期的几次作业：

作业1

设计一个类，要求有一些基本属性及两个以上的方法。（可从日常生活中抽取）在类中加入2个不同参数的构造方法。再设计一个类，包含main方法，对上面的类进行应用与测试。该作业要求编程并调试通过。对你设计的类要有详细的文字说明（类所封装的内容，属性、方法的功能与含义等）。

 

 1 public class Homework_1
 2 {
 3     public static void main(String args[])
 4     {
 5         System.out.println("Hello, Java world!");
 6         // define two complex numbers
 7         Complex a = new Complex(1.0, 1.0);
 8         Complex b = new Complex(-4.0, 3.0);
 9         Complex c;
10         // apply basic numerical operations on defined complex objects
11         System.out.println("First one:");
12         a.Show();
13         System.out.println("Second one:");
14         b.Show();
15         System.out.println("Add:");
16         c = Add(a, b);
17         c.Show();
18         System.out.println("Subtract:");
19         c = Subtract(a, b);
20         c.Show();
21         System.out.println("Multiply:");
22         c = Multiply(a, b);
23         c.Show();
24         System.out.println("Divide:");
25         c = Divide(a, b);
26         c.Show();
27     }
28     // definition of basic numerical operations
29     private static Complex Add(Complex a, Complex b)
30     {
31         return new Complex(a.real + b.real, a.imag + b.imag);
32     }
33     private static Complex Subtract(Complex a, Complex b)
34     {
35         return new Complex(a.real - b.real, a.imag - b.imag);
36     }
37     private static Complex Multiply(Complex a, Complex b)
38     {
39         return new Complex(a.real * b.real - a.imag * b.imag, a.real * b.imag + a.imag * b.real);
40     }
41     private static Complex Divide(Complex a, Complex b)
42     {
43         return new Complex((a.real * b.real + a.imag * b.imag) / b.Magnitude(), 
44                 (a.imag * b.real - a.real * b.imag) / b.Magnitude());
45     }
46 }
47 
48 // Complex number class
49 class Complex
50 {
51     // definition of real and imaginary part
52     double real, imag;
53     // construction
54     Complex(double a, double b)
55     {
56         real = a;
57         imag = b;
58     }
59     // calculate angle
60     double Angle()
61     {
62         return Math.atan(imag / real);
63     }
64     // calculate magnitude
65     double Magnitude()
66     {
67         return Math.sqrt(real * real + imag * imag);
68     }
69     // show this number
70     void Show()
71     {
72         System.out.println("Complex Number: " + real + " + " + imag + "i\n");
73     }
74 }

 

作业2：设计一个处理复数运算的类，该类中至少有两个成员方法：复数加法和复数减法运算。在上述类中添加两个静态方法：求一个复数的模和求一个复数的复角。设计一个子类，该子类继承了上述的类，并且至少拥有自己的两个方法：复数乘法和复数除法。再设计一个类，包含main方法，对上面的类进行应用与测试。

 

 1 public class Homework_2
 2 {
 3     public static void main(String args[])
 4     {
 5         System.out.println("Hello, Java world!");
 6         // define two complex numbers
 7         newComplex a = new newComplex(); a.real = 0; a.imag = 1;
 8         // apply basic numerical operations on defined complex objects
 9         System.out.println("First one:");
10         a.Show();
11         System.out.println("Second one:");
12         System.out.println("Add:");
13         a.Add(0, 1);
14         a.Show();
15         System.out.println("Subtract:");
16         a.Subtract(0, 1);
17         a.Show();
18         System.out.println("Multiply:");
19         a.Multiply(0, 1);
20         a.Show();
21         System.out.println("Divide:");
22         a.Divide(0, 1);
23         a.Show();
24     }
25 }
26 
27 // Complex number class
28 class Complex
29 {
30     // definition of real and imaginary part
31     double real, imag;
32     // calculate angle
33     double Angle()
34     {
35         return Math.atan(imag / real);
36     }
37     // calculate magnitude
38     double Magnitude()
39     {
40         return Math.sqrt(real * real + imag * imag);
41     }
42     // show this number
43     void Show()
44     {
45         System.out.println("Complex Number: " + real + " + " + imag + "i\n");
46     }
47     // basic numerical operations
48     void Add(double a, double b)
49     {
50         real = real + a;
51         imag = imag + b;
52     }
53     void Subtract(double a, double b)
54     {
55         real = real - a;
56         imag = imag - b;
57     }
58 }
59 
60 //new complex number class
61 class newComplex extends Complex
62 {
63     // more advanced operations
64     void Multiply(double a, double b)
65     {
66         double new_real = real * a - imag * b, new_imag = real * b + imag * a;
67         real = new_real;
68         imag = new_imag;
69     }
70     void Divide(double a, double b)
71     {
72         Complex c = new Complex(); c.real = a; c.imag = b;
73         double new_real = (real * a + imag * b) / c.Magnitude();
74         double new_imag = (imag * a - real * b) / c.Magnitude();
75         real = new_real;
76         imag = new_imag;
77     }
78 }

 

作业3：编写一个线段类 MyLine，要求如下：主要属性有： x ，y ；类型为Point (查看API)。编写构造方法，如 MyLine(Point  p1 , Point p2)。编写5个成员方法。如：检查线段是否位于第一象限check()…求线段的长度 length()…判断两条直线是否相交(另一线段作为参数)。编写一点到该线段（或延长线）的距离，其他方法。注：编写方法时，考虑利用Point类的方法。编写测试程序。

 

  1 import java.awt.Point;
  2 
  3 public class Homework_3
  4 {
  5     public static void main(String args[])
  6     {
  7         System.out.println("Hello, Java world!");
  8         // define two points
  9         Point a = new Point(1, 3);
 10         Point b = new Point(3, 1);
 11         MyLine l = new MyLine(a, b);
 12         // test if in the first quadrant
 13         if (l.if_first_Quadrant())
 14             System.out.println("This line is in the first quadrant!");
 15         else
 16             System.out.println("This line is not in the first quadrant!");
 17         // print the length of this line
 18         System.out.println("The length of this line is " + l.length());
 19         // print the mid point of this line
 20         Point c = l.midPoint();
 21         System.out.println("The mid point is (" + c.getX() + ", " + c.getY() + ")");
 22         // print the slope of this line
 23         System.out.println("The slope of this line is " + l.direction());
 24         // check if the mid point is on the line
 25         if (l.if_on_line(c))
 26             System.out.println("The mid point is on this line!");
 27         else
 28             System.out.println("The mid point is not on this line!");
 29     }
 30 }
 31 
 32 // MyLine class
 33 class MyLine
 34 {
 35     // definition of x and y
 36     Point x, y;
 37     
 38     MyLine(Point p1, Point p2)
 39     {
 40         x = p1; y = p2;
 41     }
 42     
 43     // check if this line is in the first Quadrant 
 44     boolean if_first_Quadrant()
 45     {
 46         if (x.getX() > 0 && x.getY() > 0 && y.getX() > 0 && y.getY() > 0)
 47             return true;
 48         else
 49             return false;
 50     }
 51     
 52     // return the length of this line
 53     double length()
 54     {
 55         return Math.sqrt((x.getX() - y.getX()) * (x.getX() - y.getX()) +
 56                 (x.getY() - y.getY()) * (x.getY() - y.getY()));
 57     }
 58     
 59     // return midPoint on this line
 60     Point midPoint()
 61     {
 62         return new Point ((int)((x.getX() + y.getX()) / 2), (int)(x.getY() + y.getY()) / 2);
 63     }
 64     
 65     // return direction of the line
 66     double direction()
 67     {
 68         return (x.getY() - y.getY()) / (x.getX() - y.getX());
 69     }
 70     
 71     // check if given point is on this line
 72     boolean if_on_line(Point p)
 73     {
 74         if ((p.getX() < x.getX() && p.getX() < y.getX()) ||
 75                 (p.getX() > x.getX() && p.getX() > y.getX()))
 76             return false;
 77         else if ((x.getY() - y.getY()) / (x.getX() - y.getX()) == (x.getY() - p.getY()) / (x.getX() - p.getX()))
 78             return true;
 79         return false;
 80     }
 81 }
 82 
 83 // Complex number class
 84 class Complex
 85 {
 86     // definition of real and imaginary part
 87     double real, imag;
 88     // calculate angle
 89     double Angle()
 90     {
 91         return Math.atan(imag / real);
 92     }
 93     // calculate magnitude
 94     double Magnitude()
 95     {
 96         return Math.sqrt(real * real + imag * imag);
 97     }
 98     // show this number
 99     void Show()
100     {
101         System.out.println("Complex Number: " + real + " + " + imag + "i\n");
102     }
103     // basic numerical operations
104     void Add(double a, double b)
105     {
106         real = real + a;
107         imag = imag + b;
108     }
109     void Subtract(double a, double b)
110     {
111         real = real - a;
112         imag = imag - b;
113     }
114 }
115 
116 //new complex number class
117 class newComplex extends Complex
118 {
119     // more advanced operations
120     void Multiply(double a, double b)
121     {
122         double new_real = real * a - imag * b, new_imag = real * b + imag * a;
123         real = new_real;
124         imag = new_imag;
125     }
126     void Divide(double a, double b)
127     {
128         Complex c = new Complex(); c.real = a; c.imag = b;
129         double new_real = (real * a + imag * b) / c.Magnitude();
130         double new_imag = (imag * a - real * b) / c.Magnitude();
131         real = new_real;
132         imag = new_imag;
133     }
134 }

 

作业4：完成一个application图形界面程序。用户界面要求见如下两图：

 

 

功能说明：

file菜单包括两个菜单项（图1）：

open：打开.gif的图形文件，并显示在窗口里。文件名在下面的编辑框中给出（如p1)

exit：结束程序。

edit菜单—包括两个菜单项（图2）：

paint：在窗口中画图形，图形的类型及颜色分别由下面的复选框及选择按扭指定。

clear：清空窗口内容。

该作业要求编程并调试通过。对你设计的类要有详细的文字说明（类所封装的内容，属性、方法的功能与含义等）。

  1 import java.awt.*;
  2 import java.awt.event.ActionEvent;
  3 import java.awt.event.ActionListener;
  4 import javax.swing.*;
  5 
  6 public class Homework_4
  7 {
  8     // create a simple GUI window
  9     public static void main(String[] args)
 10     {
 11         MyFrame myFrame = new MyFrame();
 12     }
 13     
 14 }
 15 
 16 class MyFrame extends JFrame
 17 {
 18     private JLabel label;
 19     private JFileChooser fileChooser;
 20     private JTextArea textArea;
 21     private JComboBox comboBox;
 22     private ButtonGroup buttonGroup;
 23     private String color, shape;
 24     
 25     public MyFrame()
 26     {
 27         // create and setup the window
 28         super("Menu Frame");
 29         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 30         setLocation(300, 300);
 31         setSize(new Dimension(700, 500));
 32         setResizable(false);
 33         try
 34         {
 35             UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
 36         }
 37         catch (Exception e)
 38         {
 39             System.out.println("Cannot adapt look and feel.\n");
 40         }
 41                 
 42         // create menu bar
 43         JMenuBar menuBar = new JMenuBar();
 44         JMenu fileMenu = new JMenu("File");
 45         menuBar.add(fileMenu);
 46         JMenu editMenu = new JMenu("Edit");
 47         menuBar.add(editMenu);
 48         setJMenuBar(menuBar);
 49         
 50         // create and setup open menu item
 51         JMenuItem openMenuItem = new JMenuItem("Open");
 52         openMenuItem.addActionListener(new ImageOpenListener());
 53         fileMenu.add(openMenuItem);
 54         
 55         // create and setup exit menu item
 56         JMenuItem exitMenuItem = new JMenuItem("Exit");
 57         exitMenuItem.addActionListener(new ActionListener()
 58         {
 59             public void actionPerformed(ActionEvent e)
 60             {
 61                 System.exit(0);
 62             }
 63         });
 64         fileMenu.add(exitMenuItem);
 65         
 66         // create paint menu item
 67         JMenuItem paintMenuItem = new JMenuItem("Paint");
 68         paintMenuItem.addActionListener(new ActionListener()
 69         {
 70             public void actionPerformed(ActionEvent e)
 71             {
 72                 textArea.setText(null);
 73                 color = buttonGroup.getSelection().getActionCommand();
 74                 shape = (String) comboBox.getSelectedItem();
 75                 label.setIcon(new MyShape(400, 300));
 76                 label.setHorizontalAlignment(SwingConstants.CENTER);
 77             }
 78         });
 79         editMenu.add(paintMenuItem);
 80         
 81         // create clear menu item
 82         JMenuItem clearMenuItem = new JMenuItem("Clear");
 83         clearMenuItem.addActionListener(new ActionListener()
 84         {
 85             public void actionPerformed(ActionEvent e)
 86             {
 87                 label.setText(null);
 88                 label.setIcon(null);
 89                 textArea.setText(null);
 90             }
 91         });
 92         editMenu.add(clearMenuItem);
 93 
 94         // create label and file chooser to display a image
 95         label = new JLabel();
 96         getContentPane().add(label, BorderLayout.NORTH);
 97         fileChooser=new JFileChooser();
 98         
 99         // create text area
100         textArea = new JTextArea(1, 50);
101         textArea.setEnabled(false);
102         
103         // create combo box
104         comboBox = new JComboBox();
105         comboBox.addItem("oval");
106         comboBox.addItem("rectangle");
107         comboBox.addItem("triangle");
108 
109         // create radio button
110         JRadioButton radioButtonRed = new JRadioButton("red");
111         radioButtonRed.setActionCommand("red");
112         JRadioButton radioButtonYellow = new JRadioButton("Yellow");
113         radioButtonYellow.setActionCommand("yellow");
114         JRadioButton radioButtonBlue = new JRadioButton("Blue");
115         radioButtonBlue.setActionCommand("blue");
116         buttonGroup = new ButtonGroup();
117         buttonGroup.add(radioButtonRed);
118         buttonGroup.add(radioButtonYellow);
119         buttonGroup.add(radioButtonBlue);
120         radioButtonRed.setSelected(true); // set initial choice for radio button group
121 
122         // create a panel containing text area, combo box and radio choice
123         JPanel panel = new JPanel();
124         getContentPane().add(panel, BorderLayout.SOUTH);
125         panel.add(textArea, BorderLayout.WEST);
126         panel.add(comboBox, BorderLayout.CENTER);
127         panel.add(radioButtonRed, BorderLayout.EAST);
128         panel.add(radioButtonYellow, BorderLayout.EAST);
129         panel.add(radioButtonBlue, BorderLayout.EAST);
130         
131         // display the window
132         setVisible(true);
133     }
134     
135     // create listener for opening images
136     private class ImageOpenListener implements ActionListener
137     {
138         public void actionPerformed(ActionEvent e)
139         {
140             fileChooser.showOpenDialog(MyFrame.this);
141             String imageName = fileChooser.getSelectedFile().getPath();
142             ImageIcon imageIcon = new ImageIcon(imageName);
143             label.setIcon(imageIcon);
144             label.setHorizontalAlignment(SwingConstants.CENTER);
145             textArea.setText(imageName);
146         }
147     }
148     
149     // setup MyShape icon to draw different shapes with different colors
150     private class MyShape implements Icon
151     {
152         private int width, height;
153         public MyShape(int wid, int ht)
154         {
155             width = wid;
156             height = ht;
157         }
158         public void paintIcon(Component container, Graphics g, int p, int q)
159         {
160             if (color == "red")
161             {
162                 g.setColor(new Color(255, 0, 0));
163             }
164             else if (color == "yellow")
165             {
166                 g.setColor(new Color(255, 255, 0));
167             }
168             else if (color == "blue")
169             {
170                 g.setColor(new Color(0, 0, 255));
171             }
172             if (shape == "oval")
173             {
174                 g.drawOval(p, q, width - 1, height - 1);
175                 g.fillOval(p, q, width - 1, height - 1);
176             }
177             else if (shape == "rectangle")
178             {
179                 g.drawRect(p, q, width - 1, height - 1);
180                 g.fillRect(p, q, width - 1, height - 1);
181             }
182             else if (shape == "triangle")
183             {
184                 Polygon polygon = new Polygon();
185                 polygon.addPoint(150, 300);
186                 polygon.addPoint(550, 300);
187                 polygon.addPoint(300, 0);
188                 g.drawPolygon(polygon);
189                 g.fillPolygon(polygon);
190             }
191         }
192         public int getIconWidth()
193         {
194             return width;
195         }
196         public int getIconHeight()
197         {
198             return height;
199         }
200     }
201 }

 

我设计的类有 MyFrame（从 JFrame 继承而来），MyFrame 封装了 JMenuBar，JMenuItem，JLabel，JFileChooser，JTextArea，JComboBox，ButtonGroup 等类。另外我还设计了 ImageOpenListener 类（从 ActionListener 继承而来）以及 MyShape 类（从 Icon 类继承而来）用来调整所画图形的形状和颜色。

编译和运行：

 

 

作业3最终的界面展示如下：

 

 

作业5：将作业4中的程序改为 applet 小程序，并编写相应的 HTML 文件。

 

期末大作业：作业题目自定，详细说明项目的需求。
程序要有明确的功能，调试通过并能正常运行。
程序至少要包含以下知识点：
GUI 图形界面
多线程
文件I/O或网络编程
程序代码在500行以上。
作业要求：
     1、规划出实现这个项目所需要的类；
     2、根据设计要求作出类图及类相应的关系；
     3、编写代码实现设计。

 [to be continued]