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;
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"); } } |
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:
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。
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;
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。
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页-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。
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。