码迷,mamicode.com
首页 > 编程语言 > 详细

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

时间:2018-10-28 16:04:42      阅读:179      评论:0      收藏:0      [点我收藏+]

标签:something   turn   lsp   temp   seve   文件内容   计算机类   理论   通过   

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();
      }
}

检查异常后:

package 异常;

//异常示例1
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);

        }
    }
}
package 异常;

//异常示例2
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();
    }
}

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:

技术分享图片

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);
       }
}

技术分享图片

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:

技术分享图片

技术分享图片

技术分享图片

 

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:

技术分享图片

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:

技术分享图片

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:

技术分享图片

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

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

标签:something   turn   lsp   temp   seve   文件内容   计算机类   理论   通过   

原文地址:https://www.cnblogs.com/maxinlu/p/9865593.html

(0)
(0)
   
举报
评论 一句话评论(0
登录后才能评论!
© 2014 mamicode.com 版权所有  联系我们:gaon5@hotmail.com
迷上了代码!