代码

/*从键盘输入一个文件名在屏幕显示文件内容*/
import java.util.Scanner;
import java.io.File;
import java.io.*;
public class test13_3 {
    public static void Print(File file)
    {
        try{
            BufferedReader bu = new BufferedReader(new FileReader(file));
            //构造一个BufferedReader类来读取文件
            String s = null;
            while((s = bu.readLine())!=null)//readLine方法，一次读一行
                System.out.println(s);
            bu.close();
        }catch(Exception e)
        {
            e.printStackTrace();//在命令行打印异常信息在程序中出错的位置及原因
        }
    }
    public static void main(String[] args) {
        Scanner In = new Scanner(System.in);
        System.out.println("请输入文件名：");
        String str = In.next();
        String Str1 = "D:\\" + str + ".txt";//文件具体目录
        File file = new File(Str1);
        Print(file);
    }
}

import java.util.*;
import java.io.*;
public class test13_4 {
    public static void WordCount(String Str) {
        String Str1=new String();
        for(int i=0;i<Str.length();i++){
            if(Str.charAt(i)>='a'&&Str.charAt(i)<='z'||Str.charAt(i)>='A'&&Str.charAt(i)<='Z')
                Str1+=Str.charAt(i);
            else if(Str.charAt(i-1)>='a'&&Str.charAt(i-1)<='z'||Str.charAt(i-1)>='A'&&Str.charAt(i-1)<='Z')
                Str1+=' ';
        }
        String[] Str2=Str1.split(" ");
        int count;
        for(int i=0;i<Str2.length;i++) {
            System.out.print(Str2[i]+" ");
            if((i+1)%10==0)
                System.out.println();
        }
        System.out.println("文章中单词个数为："+Str2.length);
    }
    public static void SumCount(File file) throws IOException {
        try {
            BufferedReader bu=new BufferedReader(new FileReader(file));
            String s=null;
            String S1="";
            while((s=bu.readLine())!=null)
                S1=S1+s+" ";
            //System.out.println(S1);
            bu.close();
            WordCount(S1);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws IOException
    {
        Scanner In=new Scanner(System.in);
        System.out.print("请输入文本文件名：");
        String str=In.next();
        String str1="D:\\学习代码\\java-learning\\java学习\\第十三章1\\"+str+".txt";
        File file=new File(str1);
        SumCount(file);
    }
}

import java.util.*;
import java.io.*;
//利用随机函数产生20个整数，按小到大的顺序排序后写入文件，然后从文件中读取整数并显示。分别用顺序文件和随机文件的读写方式进行编程测试。
public class test13_5 {
    public static void main(String[] args) {
        ArrayList<Integer> a = new ArrayList<Integer>();
        for (int i = 1; i <= 20; i++)
            a.add((int) (Math.random() * 100));
        for (int i = 0; i < a.size(); i++)
            System.out.print(a.get(i) + " ");
        a.sort(null);
        System.out.println();
        for (int i = 0; i < a.size(); i++)
            System.out.print(a.get(i) + " ");
        //顺序文件
        try {
            FileWriter fw = new FileWriter("charset.txt");
            for (int i = 0; i < a.size(); i++)
                fw.write(Integer.toString(a.get(i)) + " ");//.write输出ASCII英文字符，不能直接输出整形
            fw.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println();
        ArrayList<Integer> a1 = new ArrayList<Integer>();   //读取的数据存储在a1中
        try {
            BufferedReader in = new BufferedReader(new FileReader("charset.txt"));//构造一个BufferedReader类来读取文件
            String s = null;
            while ((s = in.readLine()) != null)//readLine方法，一次读一行
            {
                String[] temp = s.split(" ");
                for (int j = 0; j < temp.length; j++)
                    a1.add(0, Integer.valueOf(temp[j]));
            }
            in.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        for (int i = 0; i < a.size(); i++)
            System.out.print(a1.get(i) + " ");
        System.out.println();
        //随机文件
        StringBuffer sb=new StringBuffer();
        for (int i = 0; i < a.size(); i++) {
            sb.append(a.get(i));
            sb.append(" ");
        }
        sb.append("\n");
        System.out.println(sb);
        try {
            RandomAccessFile fio = new RandomAccessFile("charset1.txt", "rw");
            fio.seek(fio.length());   //移动到文件尾部
            fio.writeBytes(sb.toString());
            fio.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}