• 实验九 异常、断言与日志


                                                          实验九 异常、断言与日志

                                                                                                      实验时间 2018-10-25

    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();

          }

    }

    对以上两个代码在编译器上进行编译,其结果如下所示:

    两个源代码在运行的时候理解了未检查异常和已检查异常,

    未检查异常的结果如下所示

    然后对程序的异常进行检查,在源程序中对其源代码进行改变,给用户一个提示,所改程序的源代码以及测试结果如下:

    ExceptionDemo1:

    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);
        }
        }
    }

    对已检查异常的测试如下:

    然后对检查出的异常再进行改正,程序源代码如下:

     ExceptionDemo2 ;

     

    import java.io.*;
    
    public class ExceptionDemo2 {
        public static void main(String args[]) throws Exception 
         {
              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();
          }
    }

    检查出的异常,再对其进行改正,运行的结果如下所示:

    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;

    l 掌握Throwable类的堆栈跟踪方法;

    测试程序结果如下:

    测试程序2:

    l Java语言的异常处理有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;

    l 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");

           }

           catch(FileNotFoundExcption 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");

         }

    }

    实验3: 编程练习

    练习1

    l 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;

    l 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。

    程序源代码:

    Main:

    package Test;
    
    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.Collections;
    import java.util.Scanner;
    
    public class Main{
        private static ArrayList<Student> studentlist;
        public static void main(String[] args) {
            studentlist = new ArrayList<>();
            Scanner scanner = new Scanner(System.in);
            File file = new File("D:\身份证号.txt");
            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 number = linescanner.next();
                    String sex = linescanner.next();
                    String age = linescanner.next();
                    String province =linescanner.nextLine();
                    Student student = new Student();
                    student.setName(name);
                    student.setnumber(number);
                    student.setsex(sex);
                    int a = Integer.parseInt(age);
                    student.setage(a);
                    student.setprovince(province);
                    studentlist.add(student);
    
                }
            } 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();
            }
            boolean isTrue = true;
            while (isTrue) {
                System.out.println("选择你的操作,输入正确格式的选项");
                System.out.println("a.字典排序");
                System.out.println("b.输出年龄最大和年龄最小的人");
                System.out.println("c.寻找老乡");
                System.out.println("d.寻找年龄相近的人");
                System.out.println("e.退出");
                String m = scanner.next();
                switch (m) {
                case "a":
                    Collections.sort(studentlist);              
                    System.out.println(studentlist.toString());
                    break;
                case "b":
                     int max=0,min=100;
                     int j,k1 = 0,k2=0;
                     for(int i=1;i<studentlist.size();i++)
                     {
                         j=studentlist.get(i).getage();
                     if(j>max)
                     {
                         max=j; 
                         k1=i;
                     }
                     if(j<min)
                     {
                       min=j; 
                       k2=i;
                     }
                     
                     }  
                     System.out.println("年龄最大:"+studentlist.get(k1));
                     System.out.println("年龄最小:"+studentlist.get(k2));
                    break;
                case "c":
                     System.out.println("老家?");
                     String find = scanner.next();        
                     String place=find.substring(0,3);
                     for (int i = 0; i <studentlist.size(); i++) 
                     {
                         if(studentlist.get(i).getprovince().substring(1,4).equals(place)) 
                             System.out.println("老乡"+studentlist.get(i));
                     }             
                     break;
                     
                case "d":
                    System.out.println("年龄:");
                    int yourage = scanner.nextInt();
                    int near=agenear(yourage);
                    int value=yourage-studentlist.get(near).getage();
                    System.out.println(""+studentlist.get(near));
                    break;
                case "e":
                    isTrue = false;
                    System.out.println("退出程序!");
                    break;
                    default:
                    System.out.println("输入有误");
    
                }
            }
        }
            public static int agenear(int age) {      
            int j=0,min=53,value=0,k=0;
             for (int i = 0; i < studentlist.size(); i++)
             {
                 value=studentlist.get(i).getage()-age;
                 if(value<0) value=-value; 
                 if (value<min) 
                 {
                    min=value;
                    k=i;
                 } 
              }    
             return k;         
          }
    
    }

    Student:

    package Test;
    
    public class Student implements Comparable<Student> {
    
        private String name;
        private String number ;
        private String sex ;
        private int age;
        private String province;
       
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public String getnumber() {
            return number;
        }
        public void setnumber(String number) {
            this.number = number;
        }
        public String getsex() {
            return sex ;
        }
        public void setsex(String sex ) {
            this.sex =sex ;
        }
        public int getage() {
    
            return age;
            }
            public void setage(int age) {
                // int a = Integer.parseInt(age);
            this.age= age;
            }
    
        public String getprovince() {
            return province;
        }
        public void setprovince(String province) {
            this.province=province ;
        }
    
        public int compareTo(Student o) {
           return this.name.compareTo(o.getName());
        }
    
        public String toString() {
            return  name+"	"+sex+"	"+age+"	"+number+"	"+province+"
    ";
        }    
    }

    程序测试结果:

     

    注:以下实验课后完成

    练习2

    l 编写一个计算器类,可以完成加、减、乘、除的操作;

    l 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;

    l 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。

    实验的源代码如下:

    Demo:

    import java.io.FileNotFoundException;
    import java.io.PrintWriter;
    import java.util.Scanner;
    
    
    public class Demo {
        public static void main(String[] args) {
    
            Scanner in = new Scanner(System.in);
            Suanfa counter=new Suanfa();
            PrintWriter out = null;
            try {
                out = new PrintWriter("text.txt");
            } catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            int sum = 0;
    
            
            
            for (int i = 1; i <=10; i++) {
                int a = (int) Math.round(Math.random() * 100);
                int b = (int) Math.round(Math.random() * 100);
                int m= (int) Math.round(Math.random() * 3);
    
                
               switch(m)
               {
               case 0:
                   System.out.println(i+": "+a+"/"+b+"=");
                   
                   while(b==0){  b = (int) Math.round(Math.random() * 100); }
                   
                int c0 = in.nextInt();
                out.println(a+"/"+b+"="+c0);
                if (c0 == counter.division(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 1:
                   System.out.println(i+": "+a+"*"+b+"=");
                   int c = in.nextInt();
                   out.println(a+"*"+b+"="+c);
                   if (c == counter.multiplication(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(i+": "+a+"+"+b+"=");
                   int c1 = in.nextInt();
                   out.println(a+"+"+b+"="+c1);
                   if (c1 == counter.add(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(i+": "+a+"-"+b+"=");
                   int c2 = in.nextInt();
                   out.println(a+"-"+b+"="+c2);
                   if (c2 == counter.reduce(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("成绩"+sum);
            out.println("成绩:"+sum);
             out.close();
    
             
        }
        }

    suanfa:

    public class Suanfa {
       private int a;
       private int b;
        public int  add(int a,int b)
        {
            return a+b;
        }
        public int   reduce(int a,int b)
        {
            return a-b;
        }
        public int   multiplication(int a,int b)
        {
            return a*b;
        }
        public int   division(int a,int b)
        {
            if(b!=0)
            return a/b;
            else return 0;
        }
    
        
    }

    实验的结果如下所示:

    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;

    l 掌握断言的使用特点及用法。

    程序代码:

    package shiyan2;
    //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);
    
        }
    
    }

    程序测试结果:

    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;

    l 并掌握Java日志系统的用途及用法。

    实验测试结果如下:

    程序源代码:

    package logging;
    
    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)
       {
          if (System.getProperty("java.util.logging.config.class") == null
                && System.getProperty("java.util.logging.config.file") == null)
          {
             try
             {
                Logger.getLogger("com.horstmann.corejava").setLevel(Level.ALL);
                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(() ->
                {
                   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);
                });
       }
    }
    
    /**
     * The frame that shows the image.
     */
    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);
    
          // set up menu bar
          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);
                }
             });
    
          // use a label to display the images
          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);
    
             // set up file chooser
             JFileChooser chooser = new JFileChooser();
             chooser.setCurrentDirectory(new File("."));
    
             // accept all files ending with .gif
             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";
                   }
                });
    
             // show file chooser dialog
             int r = chooser.showOpenDialog(ImageViewerFrame.this);
    
             // if image file accepted, set it as icon of the label
             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");
          }
       }
    }
    
    /**
     * A handler for displaying log records in a window.
     */
    class WindowHandler extends StreamHandler
    {
       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;

    l 按课件66-77内容练习并掌握Elipse的常用调试技术。

    程序源代码

    package logging;
    
    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)
       {
          if (System.getProperty("java.util.logging.config.class") == null
                && System.getProperty("java.util.logging.config.file") == null)
          {
             try
             {
                Logger.getLogger("com.horstmann.corejava").setLevel(Level.ALL);
                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(() ->
                {
                   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);
                });
       }
    }
    
    /**
     * The frame that shows the image.
     */
    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);
    
          // set up menu bar
          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);
                }
             });
    
          // use a label to display the images
          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);
    
             // set up file chooser
             JFileChooser chooser = new JFileChooser();
             chooser.setCurrentDirectory(new File("."));
    
             // accept all files ending with .gif
             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";
                   }
                });
    
             // show file chooser dialog
             int r = chooser.showOpenDialog(ImageViewerFrame.this);
    
             // if image file accepted, set it as icon of the label
             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");
          }
       }
    }
    
    /**
     * A handler for displaying log records in a window.
     */
    class WindowHandler extends StreamHandler
    {
       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();
       }
    }

    程序测试结果如下:

    实验总结:

          通过本周的学习,对理论知识异常、日志、断言和调试的理论知识有了进一步的掌握,对理论知识的学习如下:

    异常:程序的执行过程中所发生的异常事件,它中断指令的正常执行

    Java把程序运行时可能遇到的错误分为两类:非致命异常:通过某种修正后程序还能继续执行。这类错误叫作异常。如:文件不存在、无效的数组下标、空引用、网络断开、打印机

    脱机、磁盘满等。Java中提供了一种独特的处理异常的机制,通过异常来处理程序设计中出现的错误。致命异常:程序遇到了非常严重的不正常状态,不能简单恢复执行,是致命性

    错误。如:内存耗尽、系统内部错误等。这种错误程序本身无法解决。而且其中还有异常的两种方式,比如说消极处理和积极处理两种方式。

     断言:是程序的开发和测试阶段用于插入一些代码错误检测语句的工具。

    而且使用断言必须注意两点:

     断言失败是致命的、不可恢复的错误。
    断言检查仅仅用在程序开发和测试阶段
        最后在课本所给出的实例程序中我以为检测了所学到的理论知识,对最后的断言还是有点模糊;在老师给出的任务中我也相应实践过程中学习了到了异常处理的好处,对我后期的学习会帮助很大。
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  • 原文地址:https://www.cnblogs.com/791683057mxd/p/9851708.html
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