Read and write bytes data

// Write 100000 random numbers without buffering

import java.io.*;
public class WriteUnbufferedTest

{
    public static void main(String[] args)
    {
        try{

            FileOutputStream fsout=new FileOutputStream("sample.dat");
            DataOutputStream out=new DataOutputStream(fsout);
            for(int i=0; i<100000; i++)
                out.writeDouble(Math.random());
            out.close();
        
            }catch(IOException ioe){
                System.out.println(ioe);
            }
    }

}

// Write 100000 random numbers with buffering

import java.io.*;
public class WriteBufferedTest
{
    public static void main(String[] args)
    {
        try{


            FileOutputStream fsout=new FileOutputStream("sample.dat");
            BufferedOutputStream bfsout=new BufferedOutputStream(fsout);
            DataOutputStream out=new DataOutputStream(bfsout);

            for(int i=0; i<100000; i++)
                out.writeDouble(Math.random());

            out.close();

            }catch(IOException ioe){
                System.out.println(ioe);
            }
    }
}

// Read data from data file without buffering

import java.io.*;
public class ReadUnbufferedTest  
{
    public static void main(String[] args)
    {
        double sum=0;
        try{

            FileInputStream fsin=new FileInputStream("sample.dat");
            DataInputStream in=new DataInputStream(fsin);
            for(int i=0; i<100000; i++)
                sum+=in.readDouble();
            in.close();

            }catch(IOException ioe){
                System.out.println(ioe);
            }
    }
}

// Read data with buffering

import java.io.*;
public class ReadBufferedTest  
{
    public static void main(String[] args)
    {
        double sum=0;
        try{

            FileInputStream fsin=new FileInputStream("sample.dat");
            BufferedInputStream bfsin=new BufferedInputStream(fsin);
            DataInputStream in=new DataInputStream(bfsin);
            for(int i=0; i<100000; i++)
                sum+=in.readDouble();
            in.close();

            }catch(IOException ioe){
                System.out.println(ioe);
            }
    }
}

//创建SafeCopy程序来复制文件
//这个程序可以在命令中接收源文件名和目标文件名
//只当目标文件不存在时，程序才将源文件复制到现在要创建的目标文件中去
//即不覆盖原来已存在的文件
import java.io.*;
public class SafeCopy
{
    public static void copyFile(DataInputStream in, DataOutputStream out) throws IOException
    {
        try{
            while(true)
                out.writeByte(in.readByte());
            }catch(EOFException eof){
                return;
            }
    }
    public static void main(String[] args)
    {

        String inFileName="E:\\101.asm", outFileName="E:\\500.txt";
        File inFile=new File(inFileName);
        File outFile=new File(outFileName);
        if(!inFile.exists())
            System.out.println(inFileName+"does not exist.");
        else if(outFile.exists())
            System.out.println(outFileName+"already exist.");
        else{
            try{
                FileInputStream fsin=new FileInputStream(inFileName);
                BufferedInputStream bfsin=new BufferedInputStream(fsin);
                DataInputStream in=new DataInputStream(bfsin);
                FileOutputStream fsout=new FileOutputStream(outFileName);
                BufferedOutputStream bfsout=new BufferedOutputStream(fsout);
                DataOutputStream out=new DataOutputStream(bfsout);
                copyFile(in,out);
                in.close();
                out.close();
                }catch(IOException ioe){
                    System.out.println(ioe);
                }
             }
       }
}


//用户首先输入需要复制文件的名称和路径，然后再输入新的文件名和路径，完成后将旧文件和新文件内容显示在屏幕上
import java.io.*;
public class txcopy  
{
    public static void main(String[] args)
    {
        byte[] b1=new byte[255];
        byte[] b2=new byte[255];
        byte[] b3=new byte[2056];
        byte[] b4=new byte[2056];
        int a=0;
        int b=0;
        try{
            System.out.println("请输入源文件名称: \n");
            a=System.in.read(b1,0,255);
            System.out.println("\n请输入目的文件名称: \n");
            b=System.in.read(b2,0,255);
            String sourceName=new String(b1,0,0,a-2);//把一个字节型数组转换成字符串数组
            String desName=new String(b2,0,0,b-2);
            System.out.println(sourceName.length());
            FileInputStream fileInput=new FileInputStream(sourceName);
            int bytes1=fileInput.read(b3,0,2056);
            String sourceFile=new String(b3,0,0,bytes1);
            FileOutputStream FileOutput=new FileOutputStream(desName);
            FileOutput.write(b3,0,bytes1);
            fileInput=new FileInputStream(desName);
            int bytes2=fileInput.read(b4,0,2056);
            String desFile=new String(b4,0,0,bytes2);
            System.out.println("\n源文件内容为: \n");
            System.out.println(sourceFile);
            System.out.println("\n目的文件内容: \n");
            System.out.println(desFile);
            }catch(Exception e){
                System.out.println(e.toString());
            }
    }
}

//写一个程序显示在程序的命令中指定的目录中所有的文件和目录
//包括文件大小及是文件还是目录类型
//按字母顺序排序显示，并且目录在文件之前显示
import java.io.*;
import java.util.*;
import java.io.File;
class FileNameSorter implements Comparator
{
    public int compare(Object o1, Object o2)
    {
        File f1=(File)o1;
        File f2=(File)o2;
        if(f1.isDirectory())
        {
            if(f2.isDirectory())
                return f1.getName().compareTo(f2.getName());
            else
                return -1;
        }
        else
        {
            if(f2.isDirectory())
                return 1;
            else
                return f1.getName().compareTo(f2.getName());
        }
    }
    public boolean equals(Object o1, Object o2)
    {
        return ((File)o1).getName().equals(((File)o2).getName());
    }
}
public class Dir
{
    private static void showDirInfo(File list[])
    {
        Arrays.sort(list, new FileNameSorter());
        for(int i=0; i<list.length; i++)
        {
            if(list[i].isDirectory())
                System.out.print("DIRECTORY");
            else
                System.out.print(list[i].length()+"bytes");
            System.out.println("\t"+list[i]);
        }
    }
    public static void main(String[] args)
    {
    //    File path=new File(System.getProperty("user.dir"));//用户没有提供目录，则使用当前目录
        File path=new File("D:\\j2sdk1.4.2");
        if(args.length>0)
            path=new File(args[0]);
        if(path.exists()&&path.isDirectory())
            showDirInfo(path.listFiles());
        else
            System.out.println("path not found or not directory");
    }
}