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。

import java.io.*;

public class test6_2{

public static void main(String[] args) throws IOException { String fileName = "D:\\Hello.txt";

File writer=new File(fileName);

writer.createNewFile();

BufferedWriter input = new BufferedWriter(new

FileWriter(writer));

input.write("Hello !\n");

input.write("this is my first text file,\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

import java.io.*;

class CopyMaker {

String sourceName, destName;

BufferedInputStream source;

BufferedOutputStream dest;

int line;

//打开源文件和目标文件，无异常返回true

private boolean openFiles() {

try {

source = new BufferedInputStream(new

FileInputStream( sourceName ));

}

catch ( IOException iox ) {

System.out.println("Problem opening " + sourceName );

return false;

}

try {

dest = new BufferedOutputStream(new

FileOutputStream( destName ));

}

catch ( IOException iox )

{

System.out.println("Problem opening " + destName );

return false;

}

return true;

}

//复制文件

private boolean copyFiles() {

try {

line = source.read();

while ( line != -1 ) {

dest.write(line);

line = source.read();

}

}

catch ( IOException iox ) {

System.out.println("Problem reading or writing" );

return false;

}

return true;

}

//关闭源文件和目标文件

private boolean closeFiles() {

boolean retVal=true;

try { source.close(); }

catch ( IOException iox ) {

System.out.println("Problem closing " + sourceName );

retVal = false;

}

try { dest.close(); }

catch ( IOException iox ) {

System.out.println("Problem closing " + destName );

retVal = false;

}

return retVal;

}

//执行复制

public boolean copy(String src, String dst ) {

sourceName = src ;

destName = dst ;

return openFiles() && copyFiles() && closeFiles();

}

}

//test6_2

public class test6_2

{

public static void main ( String[] args ) {

String s1="lin.txt",s2="newlin.txt";

if(new CopyMaker().copy(s1, s2))

S ystem.out.print("复制成功");

else

S ystem.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

import java.io.*;

import java.util.Random;

public class memory {

private String name;

private int count;

private int Max;

private int Min;

public memory(String n,int c,int min,int max){

https://www.360docs.net/doc/2015221877.html,=n;

this.count=c;

this.Min=min;

this.Max=max;

}

public void startmemory(){

try{

FileWriter out=new FileWriter(name);

int limit=Max-Min;

Random random = new Random();

for (int i=1;i<=count;i++){

int number=Min+random.nextInt(limit);

System.out.print(number);

System.out.print(" ");

out.write(number+" ");

}

out.close();

}catch(IOException iox){

System.out.println("方法startmemory()有问题");

}

}

}

//test6_3

import java.io.*;

import java.util.Scanner;

public class test6_3 {

public static void main(String[] args) throws IOException{ //BufferedReader

String fileName;

int count,min,max;

Scanner in = new Scanner(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();

memory M=new memory(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

import java.io.*;

public class fileWriter {

public static void main(String[] args) throws IOException{ long time = System.currentTimeMillis();//当前时间

FileWriter filewriter=new FileWriter("filewriter.txt");

int number;

for(int i=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

import java.io.*;

public class bufferedWriter {

public static void main(String[] args) throws IOException{ long time = System.currentTimeMillis();//当前时间

BufferedWriter filewriter=new BufferedWriter(new

FileWriter("filewriter.txt"));

int number;

for(int i=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。

的幂次（0~9）的表格如下：

//test6_5类

import java.io.*;

public class test6_5{

public static void main(String[] args) throws IOException{

BufferedWriter fuck =new BufferedWriter( new

FileWriter("6_5.html"));

fuck.write("

height=250>");

fuck.newLine();

fuck.write("

");

for (int i=0;i<=9;i++){

fuck.write("

");

}

fuck.write("

Power of 2 align=center>Value

"+i+" align=center>"+Math.pow(i, 2)+"

");

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_6

import java.io.*;

public class test6_6 {

public static void main(String[] args)throws IOException { FileReader fr=new FileReader("naruto.txt");

int s;

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_7

import java.io.*;

import java.util.Scanner;

public class test6_7 {

//将字符串存入文件

public static void WriteToFile(String s,String fileName){

t ry{

FileWriter writer = new FileWriter(fileName);

writer.write(s);

writer.close();

}catch (IOException iox){

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

public static String ReadFromFile(String fileName){

S tring s=new String();

t ry{

BufferedReader in = new BufferedReader(new FileReader(fileName));

s=in.readLine();

}catch(IOException io){

System.out.println("从文件中读出字符串时出错！");

}

return s;

}

//将字符串排序，然后返回字符串

public static String sort(String s){

c har[] c=s.toCharArray(); //将字符串转换成字符数组

char temp;

for(int i=0;i

for(int j=i+1;j

if(c[i]>c[j])

{

temp=c[i];

c[i]=c[j];

c[j]=temp;

}

s=new String(c); //注意不能用c.toString

return s;

}

public static void main(String args[]){

S canner in=new Scanner(System.in);

S tring s=in.next();//从键盘输入一组字符

W riteToFile(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.txt

System.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

import java.io.Serializable;

class Student implements Serializable{

String name;

int age;

int grade;

transient String secret;

public Student(String name,int age,int grade,String secret){ https://www.360docs.net/doc/2015221877.html,=name;

this.age=age;

this.grade=grade;

this.secret=secret;

}

}

//test6_8

import java.io.*;

public class tset6_8 {

public static void main(String[] args) throws

IOException,ClassNotFoundException{

Student student[]={

new Student("苍井空",19,101,"changjingkong"),

new Student("吉沢明",19,103,"jizeming"),

new Student("武藤兰",20,104,"wutenglan"),

new Student("我爱女优",21,105,"woainvyou")};

//创建输出

ObjectOutputStream oos=new ObjectOutputStream(

new FileOutputStream("naruto.dat"));

for(int i=0;i

o os.writeObject(student[i]);

oos.close();

//将对象数组student全部清空，后边你会明白的。

for(int i=0;i

s tudent[i]=null;

//创建输入

ObjectInputStream ois=new ObjectInputStream(

new FileInputStream("naruto.dat"));

for(int i=0;i

s tudent[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(int i=0;i

i f(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();

}

e lse{

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

import java.io.*;

import java.util.zip.*;

public class test6_9f{

public static void main(String[] args) throws IOException { long time = System.currentTimeMillis();

FileInputStream in = new FileInputStream("naruto.txt");

GZIPOutputStream out = new GZIPOutputStream(

new FileOutputStream("test.gz"));

System.out.println("Writing compressing file from naruto.txt to test.gz");

int c;

while((c = in.read()) != -1) out.write(c); //写压缩文件

in.close();

out.close();

System.out.println("Reading file form test.gz to monitor");

BufferedReader in2 = new BufferedReader(

new InputStreamReader(

new GZIPInputStream(

new

FileInputStream("test.gz"))));

String s;

while((s = in2.readLine()) != null) System.out.println(s);

in2.close();

System.out.println("Writing decompression to newnaruto.txt");

GZIPInputStream in3=new GZIPInputStream(

new FileInputStream("test.gz")); FileOutputStream out2=new FileOutputStream("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

import java.io.*;

import java.util.zip.*;

public class test6_9b{

public static void main(String[] args) throws IOException {

BufferedInputStream in = new BufferedInputStream(new FileInputStream("naruto.txt"));

GZIPOutputStream out = new GZIPOutputStream(

new BufferedOutputStream(

new FileOutputStream("test.gz"))); System.out.println("Writing compressing file from naruto.txt to test.gz");

int c;

long time = 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("Reading file form test.gz to monitor");

BufferedReader in2 = new BufferedReader(

new InputStreamReader(

new GZIPInputStream(

new

FileInputStream("test.gz"))));

String s;

while((s = in2.readLine()) != null) System.out.println(s);

in2.close();

//将压缩恢复

System.out.println("Writing decompression to newnaruto.txt");

GZIPInputStream in3=new GZIPInputStream(

new FileInputStream("test.gz")); BufferedOutputStream out2=new BufferedOutputStream(

new FileOutputStream("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

public class Thing{

char Name[]=new char[8];//16个字节

int Number; //4个字节

double Price;//8个字节

int Count;//4个字节所以保存一个商品要32个字节

public Thing(String name,int number,double price,int count){

if(name.toCharArray().length>8)

System.arraycopy(name.toCharArray(),0, https://www.360docs.net/doc/2015221877.html,, 0,8);//如果字符长度大于8，只取前8个

else

System.arraycopy(name.toCharArray(),0,https://www.360docs.net/doc/2015221877.html,,0,name.toCharArra y().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;

}

public String getName() {

return new String(https://www.360docs.net/doc/2015221877.html,);

}

public void setName(String name) {

if(name.toCharArray().length>8)

System.arraycopy(name.toCharArray(),0, https://www.360docs.net/doc/2015221877.html,, 0,8);

else

System.arraycopy(name.toCharArray(),0,https://www.360docs.net/doc/2015221877.html,,0,name.toCharArra y().length);

}

public double getPrice() {

return Price;

}

public void setPrice(double price) {

this.Price = price;

}

public int getNumber() {

return Number;

}

public void setNumber(int number) {

this.Number = number;

}

public int getCount() {

return Count;

}

public void setCount(int count) {

this.Count = count;

}

}

//操作Work类（包含输入、查询、更改操作）

import java.io.*;

public class Work{

String FileName;

public Work(String FileName){

this.FileName=FileName;

}

//写第n条商品记录

public void writeThing(Thing th,int n) throws Exception { RandomAccessFile rafw=new RandomAccessFile(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(int i=0;i<8;i++)

rafw.writeChar (https://www.360docs.net/doc/2015221877.html,[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

public void readThing(int n) throws Exception {

char thingname[]=new char[8];

RandomAccessFile rafr=new RandomAccessFile(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(int i=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

public void setThingName(int n,String name) throws Exception { RandomAccessFile rafw=new RandomAccessFile(FileName,"rw");

rafw.seek(n*32);

char[] borrow=new char[8];

if(name.toCharArray().length>8)

System.arraycopy(name.toCharArray(),0,borrow,0,8);

else

System.arraycopy(name.toCharArray(),0,borrow,0,name.toCharArray() .length);

for(int i=0;i<8;i++)

rafw.writeChar (borrow[i]);

rafw.close();

}

//修改存入n号商品价格

public void setThingPrice(int n,double price) throws Exception { RandomAccessFile rafw=new RandomAccessFile(FileName,"rw");

rafw.seek(n*32+8+4); //将位置指示器移到指定位置上，每个商品占24个字节，名字占8字节

rafw.writeDouble(price);

rafw.close();

}

//修改存入n号商品库存量

public void setThingCount(int n,int count) throws Exception { RandomAccessFile rafw=new RandomAccessFile(FileName,"rw");

rafw.seek(n*32+8+4+8); //将位置指示器移到指定位置上，每个商品占24个字节，名字占8字节

rafw.writeFloat(count);

rafw.close();

}

}

//test6_10

import java.util.Scanner;

public class test6_10{

public static void main(String[] args)throws Exception { Scanner scanner=new Scanner(System.in);

int number;

String name;

Work work=new Work("d:/naruto.txt");

Thing[] thing={

new Thing("立白洗衣粉",1,3.5,55),

new Thing("编辑者林楚金",2,0,0),

new Thing("舒肤佳",4,8.9,89),

new Thing("杜蕾丝超薄系列",5,1.2,444444),};

for(int i=0;i

work.writeThing(thing[i],i);

for(int i=0;i

work.readThing(i);

System.out.println("请输入要查询商品编号");

number=scanner.nextInt();

work.readThing(number-1);

System.out.println("请输入要修改某一商品名字：编号和名字");

number=scanner.nextInt();

name=scanner.next();

work.setThingName(number-1,name);

work.readThing(number-1);

}

}

运行结果：