实验部分

1、实验目的与要求

(1) 掌握java异常处理技术;

(2) 了解断言的用法;

(3) 了解日志的用途;

(4) 掌握程序基础调试技巧;

2、实验内容和步骤

实验1:用命令行与IDE两种环境下编辑调试运行源程序ExceptionDemo1、ExceptionDemo2,结合程序运行结果理解程序,掌握未检查异常和已检查异常的区别。

//异常示例1

public class ExceptionDemo1 {

public static void main(String args[]) {

int a = 0;

System.out.println(5 / a);

}

}

//异常示例2

import java.io.*;

 

public class ExceptionDemo2 {

public static void main(String args[])

     {

          FileInputStream fis=new FileInputStream("text.txt");//JVM自动生成异常对象

          int b;

          while((b=fis.read())!=-1)

          {

              System.out.print(b);

          }

          fis.close();

      }

}

修改后:

public class ExceptionDemo1 {

    public static void main(String[] args) {
        int a = 0;
        if(a==0) {
            System.out.println("除数为零");
        }
        else
        {
            System.out.println(5 / a);
        }
        
    }

}
import java.io.*;

public class ExceptionDemo2{ 
    public static void main(String args[])  
     {
          FileInputStream fis;
        try {
          fis = new FileInputStream("text.txt"); 
          int b;
          while((b=fis.read())!=-1)
          {
              System.out.print(b);
          }
          fis.close();
        }catch (Exception e) {
              // TODO Auto-generated catch block
              e.printStackTrace();//打印堆栈信息
//            System.out.println("Hello.");
        }//JVM自动生成异常对象
     }
}

实验2 导入以下示例程序,测试程序并进行代码注释。

测试程序1:

l 在elipse IDE中编辑、编译、调试运行教材281页7-1,结合程序运行结果理解程序;

l 在程序中相关代码处添加新知识的注释;

掌握Throwable类的堆栈跟踪方法;

import java.util.*;

/**
 * A program that displays a trace feature of a recursive method call.
 * @version 1.01 2004-05-10
 * @author Cay Horstmann
 */
public class StackTraceTest
{
   /**
    * Computes the factorial of a number
    * @param n a non-negative integer
    * @return n! = 1 * 2 * . . . * n
    */
   public static int factorial(int n)//求阶乘
   {
      System.out.println("factorial(" + n + "):");
      Throwable t = new Throwable();
      StackTraceElement[] frames = t.getStackTrace();//创建一个表示指定执行点的堆栈跟踪元素,t存放方法调用栈的信息
      for (StackTraceElement f : frames)
         System.out.println(f);
      int r;
      if (n <= 1) r = 1;
      else r = n * factorial(n - 1);//计算n个数的阶乘需要调用之前n-1个数的阶乘
      System.out.println("return " + r);
      return r;
   }

   public static void main(String[] args)
   {
      Scanner in = new Scanner(System.in);
      System.out.print("Enter n: ");
      int n = in.nextInt();
      factorial(n);
   }
}

测试程序2:

l Java语言的异常处理积极处理方法和消极处理两种方式

l 下列两个简答程序范例给出了两种异常处理的代码格式。在elipse IDE中编辑、调试运行源程序ExceptionalTest.java,将程序中的text文件更换为身份证号.txt,要求将文件内容读入内容,并在控制台显示;

掌握两种异常处理技术的特点。

//积极处理方式  

import java.io.*;

 

class ExceptionTest {

public static void main (string args[])

   {

       try{

       FileInputStream fis=new FileInputStream("text.txt");

       }

       catchFileNotFoundExcption e

     {   ……  }

……

    }

}

//消极处理方式

 

import java.io.*;

class ExceptionTest {

public static void main (string args[]) throws  FileNotFoundExcption

     {

      FileInputStream fis=new FileInputStream("text.txt");

     }

}

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;

public class ExceptionalTest {
    public static void main(String args[]) {
         try {
                FileInputStream fis = new FileInputStream("身份证号.txt");
                BufferedReader in = new BufferedReader(new InputStreamReader(fis));
                String a,b = new String();
                while ((a = in.readLine()) != null) {
                    b += a + "\n ";
                }
                in.close();
                System.out.println(b);

            } catch (FileNotFoundException e) {
                System.out.println("学生信息文件找不到");
                e.printStackTrace();
            } catch (IOException e) {
                System.out.println("学生信息文件读取错误");
                e.printStackTrace();
            }
        }
        }
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;

public class ExceptionalTest {
    public static void main(String[] args) throws IOException {
        FileInputStream fis = new FileInputStream("身份证号.txt");
        BufferedReader in = new BufferedReader(new InputStreamReader(fis));
        String a, b = new String();
        while ((a = in.readLine()) != null) {
            b += a+ "\n ";
        }
        in.close();
        System.out.println(b);
    }
}

实验3: 编程练习

练习1

编制一个程序,将身份证号.txt 中的信息读入到内存中;

l 按姓名字典序输出人员信息;

l 查询最大年龄的人员信息;

l 查询最小年龄人员信息;

输入你的年龄,查询身份证号.txt中年龄与你最近人的姓名、身份证号、年龄、性别和出生地;

l 查询人员中是否有你的同乡;

l 在以上程序适当位置加入异常捕获代码。

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;
import java.util.Collections;//对集合进行排序、查找、修改等;

public class Test {
    private static ArrayList<Citizen> citizenlist;

    public static void main(String[] args) {
        citizenlist = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        File file = new File("E:/java/身份证号.txt");
        //异常捕获
        try {
            FileInputStream fis = new FileInputStream(file);
            BufferedReader in = new BufferedReader(new InputStreamReader(fis));
            String temp = null;
            while ((temp = in.readLine()) != null) {

                Scanner linescanner = new Scanner(temp);

                linescanner.useDelimiter(" ");
                String name = linescanner.next();
                String id = linescanner.next();
                String sex = linescanner.next();
                String age = linescanner.next();
                String birthplace = linescanner.nextLine();
                Citizen citizen = new Citizen();
                citizen.setName(name);
                citizen.setId(id);
                citizen.setSex(sex);
                // 将字符串转换成10进制数
                int ag = Integer.parseInt(age);
                citizen.setage(ag);
                citizen.setBirthplace(birthplace);
                citizenlist.add(citizen);

            }
        } catch (FileNotFoundException e) {
            System.out.println("信息文件找不到");
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("信息文件读取错误");
            e.printStackTrace();
        }
        boolean isTrue = true;
        while (isTrue) {

            System.out.println("1.按姓名字典序输出人员信息");
            System.out.println("2.查询最大年龄的人员信息、查询最小年龄人员信息");
            System.out.println("3.查询人员中是否查询人员中是否有你的同乡");
            System.out.println("4.输入你的年龄,查询文件中年龄与你最近人的姓名、身份证号、年龄、性别和出生地");
            System.out.println("5.退出");
            int nextInt = scanner.nextInt();
            switch (nextInt) {
            case 1:
                Collections.sort(citizenlist);
                System.out.println(citizenlist.toString());
                break;
            case 2:
                int max = 0, min = 100;
                int m, k1 = 0, k2 = 0;
                for (int i = 1; i < citizenlist.size(); i++) {
                    m = citizenlist.get(i).getage();
                    if (m > max) {
                        max = m;
                        k1 = i;
                    }
                    if (m < min) {
                        min = m;
                        k2 = i;
                    }
                }
                System.out.println("年龄最大:" + citizenlist.get(k1));
                System.out.println("年龄最小:" + citizenlist.get(k2));
                break;
            case 3:
                System.out.println("出生地:");
                String find = scanner.next();
                String place = find.substring(0, 3);
                for (int i = 0; i < citizenlist.size(); i++) {
                    if (citizenlist.get(i).getBirthplace().substring(1, 4).equals(place))
                        System.out.println("出生地" + citizenlist.get(i));
                }
                break;
            case 4:
                System.out.println("年龄:");
                int yourage = scanner.nextInt();
                int near = peer(yourage);
                int j = yourage - citizenlist.get(near).getage();
                System.out.println("" + citizenlist.get(near));
                break;
            case 5:
                isTrue = false;
                System.out.println("程序已退出!");
                break;
            default:
                System.out.println("输入有误");
            }
        }
    }

    public static int peer(int age) {
        int flag = 0;
        int min = 53, j = 0;
        for (int i = 0; i < citizenlist.size(); i++) {
            j = citizenlist.get(i).getage() - age;
            if (j < 0)
                j = -j;
            if (j < min) {
                min = j;
                flag = i;
            }
        }
        return flag;
    }
}
public class Citizen implements Comparable<Citizen> {

    private String name;
    private String id;
    private String sex;
    private int age;
    private String birthplace;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public int getage() {
        return age;
    }

    public void setage(int age) {
        this.age = age;
    }

    public String getBirthplace() {
        return birthplace;
    }

    public void setBirthplace(String birthplace) {
        this.birthplace = birthplace;
    }

    public int compareTo(Citizen other) {
        return this.name.compareTo(other.getName());
    }

    public String toString() {
        return name + "\t" + sex + "\t" + age + "\t" + id + "\t" + birthplace + "\n";
    }
}

练习2

l 编写一个计算器类,可以完成加、减、乘、除的操作;

利用计算机类,设计一个小学生100以内数的四则运算练习程序,由计算机随机产生10道加减乘除练习题,学生输入答案,由程序检查答案是否正确,每道题正确计10分,错误不计分,10道题测试结束后给出测试总分;

将程序中测试练习题及学生答题结果输出到文件,文件名为test.txt

l 在以上程序适当位置加入异常捕获代码。

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;

public class calculator {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        PrintWriter out = null;
        try {
            out = new PrintWriter("test.txt");
            int sum = 0;
            for (int i = 0; i < 10; i++) {
                int a = (int) Math.round(Math.random() * 10);
                int b = (int) Math.round(Math.random() * 10);
                int menu = (int) Math.round(Math.random() * 3);
                switch (menu) {
                case 1:
                    System.out.println(a + "+" + b + "=");
                    int c1 = in.nextInt();
                    if (c1 == (a + b)) {
                        sum += 10;
                        System.out.println("恭喜答案正确");
                    } else {
                        System.out.println("抱歉,答案错误");
                    }
                    break;
                case 2:
                    System.out.println(a + "-" + b + "=");
                    int c2 = in.nextInt();
                    if (c2 == (a - b)) {
                        sum += 10;
                        System.out.println("恭喜答案正确");
                    } else {
                        System.out.println("抱歉,答案错误");
                    }

                    break;
                case 3:
                    System.out.println(a + "*" + b + "=");
                    int c = in.nextInt();
                    if (c == a * b) {
                        sum += 10;
                        System.out.println("恭喜答案正确");
                    } else {
                        System.out.println("抱歉,答案错误");
                    }

                    break;
                case 4:
                    if (b == 0) {
                        System.out.println("除数为零");
                    } else {
                        System.out.println(a + "/" + b + "=");
                    }
                    int c4 = in.nextInt();
                    if (c4 == a / b) {
                        sum += 10;
                        System.out.println("恭喜答案正确");
                    } else {
                        System.out.println("抱歉,答案错误");
                    }

                    break;
                }
            }
            System.out.println("你的得分为" + sum);
            out.println("你的得分为" + sum);
            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

}

实验4:断言、日志、程序调试技巧验证实验。

实验程序1

 

//断言程序示例

public class AssertDemo {

    public static void main(String[] args) {        

        test1(-5);

        test2(-3);

    }

    

    private static void test1(int a){

        assert a > 0;

        System.out.println(a);

    }

    private static void test2(int a){

       assert a > 0 : "something goes wrong here, a cannot be less than 0";

        System.out.println(a);

    }

}

l 在elipse下调试程序AssertDemo,结合程序运行结果理解程序;

l 注释语句test1(-5);后重新运行程序,结合程序运行结果理解程序;

掌握断言的使用特点及用法。

实验程序2:

l 用JDK命令调试运行教材298-300页程序7-2,结合程序运行结果理解程序;

并掌握Java日志系统的用途及用法。

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.logging.*;
import javax.swing.*;

/**
 * A modification of the image viewer program that logs various events.
 * @version 1.03 2015-08-20
 * @author Cay Horstmann
 */
public class LoggingImageViewer
{
   public static void main(String[] args)
   {
       //将所有消息记录到应用程序特定的文件中
      if (System.getProperty("java.util.logging.config.class") == null
            && System.getProperty("java.util.logging.config.file") == null)
      {
         try//放入可能出错的语句
         {
            Logger.getLogger("com.horstmann.corejava").setLevel(Level.ALL);//得到日志记录器
            final int LOG_ROTATION_COUNT = 10;
            Handler handler = new FileHandler("%h/LoggingImageViewer.log", 0, LOG_ROTATION_COUNT);
            Logger.getLogger("com.horstmann.corejava").addHandler(handler);
         }
         catch (IOException e)
         {
            Logger.getLogger("com.horstmann.corejava").log(Level.SEVERE,
                  "Can't create log file handler", e);
         }
      }

      EventQueue.invokeLater(() ->//使事件派发线程上的可运行对象排队
            {
               Handler windowHandler = new WindowHandler();
               windowHandler.setLevel(Level.ALL);
               Logger.getLogger("com.horstmann.corejava").addHandler(windowHandler);

               JFrame frame = new ImageViewerFrame();
               frame.setTitle("LoggingImageViewer");
               frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

               Logger.getLogger("com.horstmann.corejava").fine("Showing frame");
               frame.setVisible(true);
            });
   }
}

/**
 * 显示图像的帧。
 */
class ImageViewerFrame extends JFrame
{
   private static final int DEFAULT_WIDTH = 300;
   private static final int DEFAULT_HEIGHT = 400;   

   private JLabel label;
   private static Logger logger = Logger.getLogger("com.horstmann.corejava");

   public ImageViewerFrame()
   {
      logger.entering("ImageViewerFrame", "<init>");      
      setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

      //设置菜单栏
      JMenuBar menuBar = new JMenuBar();
      setJMenuBar(menuBar);

      JMenu menu = new JMenu("File");
      menuBar.add(menu);

      JMenuItem openItem = new JMenuItem("Open");
      menu.add(openItem);
      openItem.addActionListener(new FileOpenListener());

      JMenuItem exitItem = new JMenuItem("Exit");
      menu.add(exitItem);
      exitItem.addActionListener(new ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               logger.fine("Exiting.");
               System.exit(0);
            }
         });

      //使用标签显示图像
      label = new JLabel();
      add(label);
      logger.exiting("ImageViewerFrame", "<init>");
   }

   private class FileOpenListener implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         logger.entering("ImageViewerFrame.FileOpenListener", "actionPerformed", event);

         //设置文件选择器
         JFileChooser chooser = new JFileChooser();
         chooser.setCurrentDirectory(new File("."));

         //接受以.gif结尾的所有文件
         chooser.setFileFilter(new javax.swing.filechooser.FileFilter()
            {
               public boolean accept(File f)
               {
                  return f.getName().toLowerCase().endsWith(".gif") || f.isDirectory();
               }

               public String getDescription()
               {
                  return "GIF Images";
               }
            });

         //显示文件选择器对话框
         int r = chooser.showOpenDialog(ImageViewerFrame.this);

         // 如果图像文件被接受,将其设置为标签的图标
         if (r == JFileChooser.APPROVE_OPTION)
         {
            String name = chooser.getSelectedFile().getPath();
            logger.log(Level.FINE, "Reading file {0}", name);
            label.setIcon(new ImageIcon(name));
         }
         else logger.fine("File open dialog canceled.");
         logger.exiting("ImageViewerFrame.FileOpenListener", "actionPerformed");
      }
   }
}

/**
 * 用于在窗口中显示日志记录的处理程序。
 */
class WindowHandler extends StreamHandler//继承
{
   private JFrame frame;

   public WindowHandler()
   {
      frame = new JFrame();
      final JTextArea output = new JTextArea();
      output.setEditable(false);
      frame.setSize(200, 200);
      frame.add(new JScrollPane(output));
      frame.setFocusableWindowState(false);
      frame.setVisible(true);
      setOutputStream(new OutputStream()
         {
            public void write(int b)
            {
            } // not called

            public void write(byte[] b, int off, int len)
            {
               output.append(new String(b, off, len));
            }
         });
   }

   public void publish(LogRecord record)
   {
      if (!frame.isVisible()) return;
      super.publish(record);
      flush();
   }
}

实验程序3:

l 用JDK命令调试运行教材298-300页程序7-2,结合程序运行结果理解程序;

按课件66-77内容练习并掌握Elipse的常用调试技术。

1)条件断点(有一定条件的断点):在Eclipse Java 编辑区的行头双击就会得到一个断点,代码会运行到此处时停止。

在断点处点击鼠标右键,选择最后一个“Breakpoint Properties”。

2)变量断点:在变量的值初始化,或是变量值改变时可以停止。

3)方法断点:方法断点就是将断点打在方法的入口处。

4)异常断点:当异常发生时,代码会停在异常发生处。

5)重新调试:回退时,请在需要回退的线程方法上点右键,选择“Drop to Frame”。

6)单步执行程序 

7)检查变量

8)改变变量值

 实验总结:

   通过本周的学习,我对于Java程序运行中出现的异常,断言有了初步的理解。但是在实验过程中,我发现我需要多加练习,加深理解。课下我会多加练习,对于之前所学的知识多加回顾,查漏补缺。