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。
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。
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: