RandomAccessFile类

stream流都是只读或只写的，数据流的外部文件都是顺序的，如果不创建新文件就不能更新它们。因此提供了RandomAccessFile来对文件进行读取和修改。

需要注意的是RandomAccessFile直接继承自Object，不熟与stream结构

首先，

RandomAccessFile类实现了DataInput接口和DataOutput接口。

因此可以读取基本数据类型和字符串（readInt，readDouble,readChar,readBoolean和readUTF）

也可以写基本数据类型和字符串(writeInt,writeDouble,writeChar,writeBoolean和writeUTF)

其次，

RandomAccessFile有两种模式，只读（r）和读写（rw）

RandomAccessFile(file:File,mode:String)

RandomAccessFile(nam:String,mode:String)

需要注意到，创建RandomAccessFile对象必须指定mode，

方法

close()

getFilePointer():long

read():int

read(b:byte[]):int

read(b:byte[],off:int,len:int)

seek(pos:long)              设置文件指针的位置

setLength(newLength:long)          设置文件新长度

skipBytes(int n)             跳过多少个字节

write(int n)

write(b:byte[])

write(b:byte[],off:int,len:int)

import java.io.*;
public class RandomAccessFileTest{
        public static void main(String[] args) throws IOException{
                int n =  Integer.valueOf(args[0]);
                RandomAccessFile raf = new RandomAccessFile("inout.dat","rw");
                raf.setLength(0);
                for(int i = 1; i <= n ;i++){
                        raf.writeInt(i);
                }
                System.out.println("File length:" + raf.length());
                raf.seek(0);
                System.out.println("The first num :" + raf.readInt());
                raf.seek(1*4);
                System.out.println("The second num :" + raf.readInt());
                raf.seek(9*4);
                System.out.println("The tenth num:" + raf.readInt());
                raf.writeInt(555);
                raf.seek(raf.length());
                raf.writeInt(999);
                System.out.println("File length:" + raf.length());
                raf.seek(10*4);
                System.out.println("The eleventh num:" + raf.readInt());
        }
}

 java RandomAccessFileTest 200
File length:800
The first num :1
The second num :2
The tenth num:10
File length:804
The eleventh num:555
本程序一者验证这个文件读取功能，一者验证args参数的读取