Java语言程序设计(郑莉)第六章课后习题答案

Java语言程序设计第六章课后习题答案1.将本章例6-1至6-18中出现的文件的构造方法均改为使用File类对象作为参数实现。个人理解：File类只能对整文件性质进行处理，而没法通过自己直接使用file.Read()或者是file.write()类似方法对文件内容进行写或者读取。注意：是直接;下面只提供一个例2变化，其他的你自己做，10几道啊，出这题的人真他妈有病。importjava.io.*;publicclasstest6_2{ publicstaticvoidmain(String[]args)throwsIOException{ StringfileName="D:\\Hello.txt"; Filewriter=newFile(fileName); writer.createNewFile(); BufferedWriterinput=newBufferedWriter(newFileWriter(writer)); input.write("Hello!\n"); input.write("thisismyfirsttextfile,\n"); input.write("你还好吗？\n"); input.close(); }}运行结果：（电脑系统问题，没法换行，所以一般使用BuffereWriter中newLine()实现换行）2.模仿文本文件复制的例题，编写对二进制文件进行复制的程序.//CopyMaker类importjava.io.*;classCopyMaker{StringsourceName,destName;BufferedInputStreamsource; BufferedOutputStreamdest;intline;//打开源文件和目标文件，无异常返回trueprivatebooleanopenFiles(){ try{ source=newBufferedInputStream(newFileInputStream(sourceName)); } catch(IOExceptioniox){ System.out.println("Problemopening"+sourceName);returnfalse;}try{ dest=newBufferedOutputStream(newFileOutputStream(destName));}catch(IOExceptioniox){ System.out.println("Problemopening"+destName);returnfalse;}returntrue;}//复制文件privatebooleancopyFiles(){ try{ line=source.read(); while(line!=-1){ dest.write(line); line=source.read(); } } catch(IOExceptioniox){ System.out.println("Problemreadingorwriting"); returnfalse; } returntrue; }//关闭源文件和目标文件privatebooleancloseFiles(){ booleanretVal=true; try{source.close();} catch(IOExceptioniox){ System.out.println("Problemclosing"+sourceName); retVal=false; } try{dest.close();} catch(IOExceptioniox){ System.out.println("Problemclosing"+destName); retVal=false; } returnretVal; }//执行复制publicbooleancopy(Stringsrc,Stringdst){ sourceName=src;destName=dst;returnopenFiles()&©Files()&&closeFiles();}}//test6_2publicclasstest6_2{ publicstaticvoidmain(String[]args){ Strings1="lin.txt",s2="newlin.txt"; if(newCopyMaker().copy(s1,s2)) System.out.print("复制成功"); else System.out.print("复制失败");}}运行前的两个文本：lin.txt和newlin.txt（为空）运行后：3.创建一存储若干随机整数的文本文件，文件名、整数的个数及范围均由键盘输入。//memory存储类importjava.io.*;importjava.util.Random;publicclassmemory{ privateStringname; privateintcount; privateintMax; privateintMin; publicmemory(Stringn,intc,intmin,intmax){ =n; this.count=c; this.Min=min; this.Max=max; } publicvoidstartmemory(){ try{ FileWriterout=newFileWriter(name); intlimit=Max-Min; Randomrandom=newRandom(); for(inti=1;i<=count;i++){ intnumber=Min+random.nextInt(limit); System.out.print(number); System.out.print(""); out.write(number+""); } out.close(); }catch(IOExceptioniox){ System.out.println("方法startmemory()有问题"); } }}//test6_3importjava.io.*;importjava.util.Scanner;publicclasstest6_3{ publicstaticvoidmain(String[]args)throwsIOException{ //BufferedReader StringfileName; intcount,min,max; Scannerin=newScanner(System.in); System.out.println("输入要存储的文件名"); fileName=in.next(); System.out.println("输入随机数个数"); count=in.nextInt(); System.out.println("输入随机数最小值"); min=in.nextInt(); System.out.println("输入随机数最大值"); max=in.nextInt(); memoryM=newmemory(fileName,count,min,max); M.startmemory(); }}}运行结果：naruto文件存储二进制数：4.分别使用FileWriter和BufferedWriter往文件中写入10万个随机数，比较用时的多少。//FileWriter方法importjava.io.*;publicclassfileWriter{ publicstaticvoidmain(String[]args)throwsIOException{ longtime=System.currentTimeMillis();//当前时间 FileWriterfilewriter=newFileWriter("filewriter.txt"); intnumber; for(inti=1;i<=100000;i++){ number=(int)(Math.random()*10000); filewriter.write(number+""); } filewriter.close(); time=System.currentTimeMillis()-time;//时间差 System.out.println("用时为："+time+"微秒."); } }运行结果：//BufferedWriter方法importjava.io.*;publicclassbufferedWriter{ publicstaticvoidmain(String[]args)throwsIOException{ longtime=System.currentTimeMillis();//当前时间 BufferedWriterfilewriter=newBufferedWriter(newFileWriter("filewriter.txt")); intnumber; for(inti=1;i<=100000;i++){ number=(int)(Math.random()*10000); filewriter.write(number+""); } filewriter.close(); time=System.currentTimeMillis()-time;//时间差 System.out.println("用时为："+time+"微秒."); } }运行结果：有用时可知：BufferedWriter比FileWriter写入的速度快,当需要写入大量内容,前者效率高。5.生成一html文件，使其能显示2的幂次（0~9）的表格如下：Powerof2Value0112……//test6_5类importjava.io.*;publicclasstest6_5{ publicstaticvoidmain(String[]args)throwsIOException{ BufferedWriterfuck=newBufferedWriter(newFileWriter("6_5.html")); fuck.write("<tableborder=1align=centerwidth=200height=250>"); fuck.newLine(); fuck.write("<tr><tdalign=center>Powerof2<tdalign=center>Value</tr>"); for(inti=0;i<=9;i++){ fuck.write("<tr><tdalign=center>"+i+"<tdalign=center>"+Math.pow(i,2)+"</tr>"); } fuck.write("</table>"); fuck.newLine(); fuck.close(); } }运行结果：6.用记事本程序创建一篇包含几十个英语单词的小文章，要求从屏幕输出每一个单词。//test6_6importjava.io.*;publicclasstest6_6{ publicstaticvoidmain(String[]args)throwsIOException{ FileReaderfr=newFileReader("naruto.txt"); ints; while((s=fr.read())!=-1){ if(s>='a'&&s<='z'||s>='A'&&s<='Z') System.out.print((char)s); else System.out.print("\n"); } fr.close(); }}运行结果：7.从键盘敲入一系列字母，将其存储到文件中，对其进行升序排序后，存储到另一个文件，并显示在屏幕上。//test6_7importjava.io.*;importjava.util.Scanner;publicclasstest6_7{//将字符串存入文件publicstaticvoidWriteToFile(Strings,StringfileName){ try{ FileWriterwriter=newFileWriter(fileName);writer.write(s);writer.close();}catch(IOExceptioniox){ System.out.println("写入字符串s到文件时出错！"); }}//将字符串从文件中读取出来publicstaticStringReadFromFile(StringfileName){ Strings=newString(); try{ BufferedReaderin=newBufferedReader(newFileReader(fileName));s=in.readLine();}catch(IOExceptionio){ System.out.println("从文件中读出字符串时出错！"); }returns;}//将字符串排序，然后返回字符串publicstaticStringsort(Strings){ char[]c=s.toCharArray();//将字符串转换成字符数组chartemp;for(inti=0;i<c.length-1;i++)//这里运用冒泡排序法for(intj=i+1;j<c.length;j++)if(c[i]>c[j]){temp=c[i];c[i]=c[j];c[j]=temp;}s=newString(c);//注意不能用c.toStringreturns;}publicstaticvoidmain(Stringargs[]){ Scannerin=newScanner(System.in); Strings=in.next();//从键盘输入一组字符 WriteToFile(s,"D:\\naruto.txt");//将字符串保存到D:\naruto.txt s=null;//将s清空，下面好读取，不然无法辨别s是读取到数据还是原来的数据s=ReadFromFile("D:\\naruto.txt");//从文件D:\naruto.txt读出字符串s=sort(s);//将s进行排序WriteToFile(s,"D:\\newnaruto.txt");//将排序后的内容保存到另一文件D:\newnaruto.txtSystem.out.println(s);}}运行结果：文件D:\\naruto.txt和D:\\newnaruto.txt中内容：8.创建一个学生类（包括姓名、年龄、班级、密码），创建若干该类的对象并保存在文件中（密码不保存），从文件读取对象后显示在屏幕上。//Student类importjava.io.Serializable;classStudentimplementsSerializable{ Stringname; intage; intgrade; transientStringsecret; publicStudent(Stringname,intage,intgrade,Stringsecret){ =name; this.age=age; this.grade=grade; this.secret=secret; } }//test6_8importjava.io.*;publicclasstset6_8{ publicstaticvoidmain(String[]args)throwsIOException,ClassNotFoundException{ Studentstudent[]={ newStudent("苍井空",19,101,"changjingkong"), newStudent("吉沢明",19,103,"jizeming"), newStudent("武藤兰",20,104,"wutenglan"), newStudent("我爱女优",21,105,"woainvyou")}; //创建输出 ObjectOutputStreamoos=newObjectOutputStream(newFileOutputStream("naruto.dat")); for(inti=0;i<student.length;i++) oos.writeObject(student[i]); oos.close(); //将对象数组student全部清空，后边你会明白的。 for(inti=0;i<student.length;i++) student[i]=null; //创建输入 ObjectInputStreamois=newObjectInputStream(newFileInputStream("naruto.dat")); for(inti=0;i<student.length;i++) student[i]=(Student)ois.readObject();//重新从文件中读入，之前的清空就因为此读入。注意，读入要强制转化为学生类 ois.close(); //显示信息 for(inti=0;i<student.length;i++){ if(i==student.length-1){ System.out.println("我的名字："+student[i].name); System.out.println("我的年龄："+student[i].age); System.out.println("我的班级："+student[i].grade); System.out.println("我的密码："+student[i].secret); System.out.println(); } else{ System.out.println("第"+(i+1)+"个女学生名字："+student[i].name); System.out.println("第"+(i+1)+"个女学生年龄："+student[i].age); System.out.println("第"+(i+1)+"个女学生班级："+student[i].grade); System.out.println("第"+(i+1)+"个女学生密码："+student[i].secret); System.out.println(); } } }}9.对例6—14中的压缩程序段进行修改，是压缩流经过缓冲类。比较两种方法在对大的文件进行压缩时的效率。//没经过缓冲类，使用FileInputStream类importjava.io.*;importjava.util.zip.*;publicclasstest6_9f{publicstaticvoidmain(String[]args)throwsIOException{ longtime=System.currentTimeMillis();FileInputStreamin=newFileInputStream("naruto.txt");GZIPOutputStreamout=newGZIPOutputStream(newFileOutputStream("test.gz"));System.out.println("Writingcompressingfilefromnaruto.txttotest.gz");intc;while((c=in.read())!=-1)out.write(c);//写压缩文件in.close();out.close();System.out.println("Readingfileformtest.gztomonitor");BufferedReaderin2=newBufferedReader(newInputStreamReader(newGZIPInputStream(newFileInputStream("test.gz"))));Strings;while((s=in2.readLine())!=null)System.out.println(s);in2.close();System.out.println("Writingdecompressiontonewnaruto.txt");GZIPInputStreamin3=newGZIPInputStream(newFileInputStream("test.gz"));FileOutputStreamout2=newFileOutputStream("newnaruto.txt");while((c=in3.read())!=-1)out2.write(c);in3.close();out2.close(); time=System.currentTimeMillis()-time;//时间差System.out.println("用时为："+time+"微秒.");}}运行结果：//压缩流经过缓冲类，使用BufferedInputStream类importjava.io.*;importjava.util.zip.*;publicclasstest6_9b{publicstaticvoidmain(String[]args)throwsIOException{BufferedInputStreamin=newBufferedInputStream(newFileInputStream("naruto.txt"));GZIPOutputStreamout=newGZIPOutputStream(newBufferedOutputStream( newFileOutputStream("test.gz")));System.out.println("Writingcompressingfilefromnaruto.txttotest.gz");intc;longtime=System.currentTimeMillis();//写压缩文件while((c=in.read())!=-1)out.write(c);in.close();out.close();//重新读出来System.out.println("Readingfileformtest.gztomonitor");BufferedReaderin2=newBufferedReader(newInputStreamReader(newGZIPInputStream(newFileInputStream("test.gz"))));Strings;while((s=in2.readLine())!=null)System.out.println(s);in2.close();//将压缩恢复System.out.println("Writingdecompressiontonewnaruto.txt");GZIPInputStreamin3=newGZIPInputStream(newFileInputStream("test.gz"));BufferedOutputStreamout2=newBufferedOutputStream( newFileOutputStream("newnaruto.txt"));while((c=in3.read())!=-1)out2.write(c);in3.close();out2.close(); time=System.currentTimeMillis()-time;//时间差System.out.println("用时为："+time+"微秒.");}}运行结果：以上2个类的运行用时比较，可见对大文件进行压缩，经过缓冲流的效率要高得多。10.一家杂货店的店主，需要查询、输入、修改任何一件商品的品名、价格、库存量信息。请用随机存取文件满足其要求，可以更新、查询信息。每件商品的标志为其记录号。//商品Thing类publicclassThing{ charName[]=newchar[8];//16个字节 intNumber; //4个字节 doublePrice;//8个字节 intCount;//4个字节所以保存一个商品要32个字节 publicThing(Stringname,intnumber,doubleprice,intcount){ if(name.toCharArray().length>8) System.arraycopy(name.toCharArray(),0,this.Name,0,8);//如果字符长度大于8，只取前8个 else System.arraycopy(name.toCharArray(),0,this.Name,0,name.toCharArray().length);//如果字符长度小于8，有几个填几个 this.Number=number; this.Price=price; this.Count=count; } publicStringgetName(){ returnnewString(this.Name); } publicvoidsetName(Stringname){ if(name.toCharArray().length>8) System.arraycopy(name.toCharArray(),0,this.Name,0,8); else System.arraycopy(name.toCharArray(),0,this.Name,0,name.toCharArray().length); } publicdoublegetPrice(){ returnPrice; } publicvoidsetPrice(doubleprice){ this.Price=price; } publicintgetNumber(){ returnNumber; } publicvoidsetNumber(intnumber){ this.Number=number; } publicintgetCount(){ returnCount; } publicvoidsetCount(intcount){ this.Count=count; } }//操作Work类（包含输入、查询、更改操作）importjava.io.*;publicclassWork{ StringFileName; publicWork(StringFileName){ this.FileName=FileName; } //写第n条商品记录 publicvoidwriteThing(Thingth,intn)throwsException{ RandomAccessFilerafw=newRandomAccessFile(FileName,"rw"); rafw.seek(n*32);//将位置指示器移到指定位置上，每个商品占32个字节 for(inti=0;i<8;i++) rafw.writeChar(th.Name[i]);//写入商品名 rafw.writeInt(th.Number);//写入商品号码 rafw.writeDouble(th.Price);//写入价格 rafw.writeInt(th.Count);//写入商品库存量 rafw.close(); } //输入商品信息 publicvoidreadThing(intn)throwsException{ charthingname[]=newchar[8]; RandomAccessFilerafr=newRandomAccessFile(FileName,"r"); rafr.seek(n*32);//将位置指示器移到指定位置上，每个商品占32个字节 for(inti=0;i<8;i++) thingname[i]=rafr.readChar();//读到char商品名 System.out.print("商品名:"); System.out.println(thingname); System.out.println("编号:"+rafr.readInt()); System.out.println("价格:"+rafr.readDouble()); System.out.println("商品库存量:"+rafr.readInt()); rafr.close(); System.out.println(); } //修改存入n号商品名字 publicvoidsetThi