马昕璐201771010118 《面对对象程序设计(java)》第九周学习总结

第一部分:理论知识学习部分

异常:在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。

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。

Java中的异常类可分为两大类:;

– Error

Error类层次结构描述了Java 运行时系统的内部错误和资源耗尽错误。应用程序不应该捕获这类异常,也不会抛出这种异常

– Exception

Exception类:重点掌握的异常类。Exception层次结构又分解为两个分支:一个分支派生于RuntimeException;

声明抛出异常在方法声明中用throws子句中来指明。该方法将不对这些异常进行处理,而是声明抛出它们。

Java运行系统从异常生成的代码块开始,寻找相应的异常处理代码,并将异常交给该方法处理,这一过程叫作捕获

–try语句括住可能抛出异常的代码段。

–catch语句指明要捕获的异常及相应的处理代码。

–finally语句指明必须执行的程序块。

 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。

1、assert 条件   或者

2、assert 条件:表达式

 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

第二部分: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1public class ExceptionDemo1 {    public static void main(String args[]) {        int a = 0;        System.out.println(5 / a);    }}
//异常示例2import 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();      }}

检查异常后:

package 异常;//异常示例1public 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);        }    }}
package 异常;//异常示例2import 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();    }}

在项目文件夹中添加相应的TXT文件

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:

1.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;

2.在程序中相关代码处添加新知识的注释;

3.掌握Throwable类的堆栈跟踪方法;

7-1代码如下:

package stackTrace;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)   {      System.out.println("factorial(" + n + "):");      Throwable t = new Throwable();//调用Throwable类的getStackTrace方法,得到StackTraceElement对象的一个数组      StackTraceElement[] frames = t.getStackTrace();      for (StackTraceElement f : frames)         System.out.println(f);      int r;      if (n <= 1) r = 1;      else r = n * factorial(n - 1);      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);   }}

程序运行结果如下:

测试程序2:

1.Java语言的异常处理有积极处理方法和消极处理两种方式;

2.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;

3.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");     }}

读入内容后:

package 异常;//积极处理方式  import java.io.*;import java.io.BufferedReader;import java.io.FileReader;class ExceptionTest {    public static void main (String args[]) {        File fis=new File("身份证号.txt");     try{         FileReader fr = new FileReader(fis);         BufferedReader br = new BufferedReader(fr);         try {             String s, s2 = new String();             while ((s = br.readLine()) != null) {                 s2 += s + "\n ";             }             br.close();             System.out.println(s2);         } catch (IOException e) {             // TODO Auto-generated catch block             e.printStackTrace();         }     } catch (FileNotFoundException e) {         // TODO Auto-generated catch block         e.printStackTrace();     }  }}
package 异常;//消极处理方式import java.io.*;class ExceptionTest {    public static void main (String args[]) throws  IOException       {        File fis=new File("身份证号.txt");        FileReader fr = new FileReader(fis);        BufferedReader br = new BufferedReader(fr);        String s, s2 = new String();            while ((s = br.readLine()) != null) {                s2 += s + "\n ";            }            br.close();            System.out.println(s2);       }}

实验3: 编程练习

练习1:

1.编制一个程序,将身份证号.txt 中的信息读入到内存中;

2.按姓名字典序输出人员信息;

3.查询最大年龄的人员信息;

4.查询最小年龄人员信息;

5.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;

6.查询人员中是否有你的同乡;

在以上程序适当位置加入异常捕获代码。

import java.io.File;import java.io.BufferedReader;import java.util.Scanner;import java.util.ArrayList;import java.util.Arrays;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStreamReader;import java.util.Collections;public class Test {    private static ArrayList<Student> studentlist;    public static void main(String[] args) {        studentlist = new ArrayList<>();        Scanner scanner = new Scanner(System.in);        File file = new File("F:\\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();            //加入的捕获异常代码        } catch (IOException e) {            System.out.println("学生信息文件读取错误");            e.printStackTrace();            //加入的捕获异常代码        }        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("F.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 "F":                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;    }}
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+"\t"+sex+"\t"+age+"\t"+number+"\t"+province+"\n";    }}

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。

代码:

import java.util.Scanner;import java.util.Random;import java.io.FileNotFoundException;import java.io.PrintWriter;public class jisuan {    public static void main(String[] args) {        Scanner in = new Scanner(System.in);        yunsuan counter = new yunsuan();        PrintWriter out = null;        try {            out = new PrintWriter("text.txt");        } catch (FileNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        int sum = 0;        System.out.println("随机生成的四则运算类型");        System.out.println("类型1:除法");        System.out.println("类型2:乘法");        System.out.println("类型3:加法");        System.out.println("类型4:减法");        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;            Random rand = new Random();            m = (int) rand.nextInt(4) + 1;            System.out.println("随机生成的四则运算类型:"+m);            switch (m) {            case 1:                System.out.println(i + ": " + a + "/" + b + "=");                while (b == 0) {                    b = (int) Math.round(Math.random() * 100);                }                double c0 = in.nextDouble();                out.println(a + "/" + b + "=" + c0);                if (c0 == counter.division(a, b)) {                    sum += 10;                    System.out.println("right!");                } else {                    System.out.println("error!");                }                break;            case 2:                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("right!");                } else {                    System.out.println("error!");                }                break;            case 3:                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("right!");                } else {                    System.out.println("error!");                }                break;            case 4:                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("right!");                } else {                    System.out.println("error!");                }                break;            }        }        System.out.println("成绩" + sum);        out.println("成绩:" + sum);        out.close();    }}
public class yunsuan {    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;}    }

运行结果:

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。

运行结果如下:

package stackTrace;//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);  }}

运行结果如下:

实验程序2:

l 用JDK命令调试运行教材298页-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。

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();   }}LoggingImageViewer

程序运行结果如下:

实验程序3:

l 用JDK命令调试运行教材298页-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。

4. 实验总结:

本周主要讲了异常方面的知识,学习了异常的处理方法,但感觉对内容方面还有不懂的地方,尤其对代码应用方面,仍需研究